Subthreshold attention deficit hyperactivity in children and adolescents: a systematic review

REVIEW

Subthreshold attention deficit hyperactivity in childrenand adolescents: a systematic review

Judit Balazs • Agnes Kereszteny

Received: 2 September 2013 / Accepted: 27 December 2013

� Springer-Verlag Berlin Heidelberg 2014

Abstract Subthreshold disorders, conditions with rele-

vant psychiatric symptoms which do not meet the full

criteria of a disorder according to the prevailing classifi-

cation systems, have received increased attention recently.

The current paper aims to present a systematic review of

subthreshold attention-deficit/hyperactivity disorder

(ADHD) in children and adolescents. Searching five com-

puterised databases (Ovid MEDLINE, Psychinfo, PubMed,

Scopus, Web of Science) with two categories of search

terms [(1) subclinical; subsyndromal; subthreshold (2)

ADHD] the authors examined the prevalence of sub-

threshold ADHD among children and adolescents, the

comorbidity of subthreshold ADHD and whether there was

already any impact of subthreshold ADHD on functioning.

Before these questions were answered, the included articles

were examined to see what kinds of definitions of child and

adolescent subthreshold ADHD are used and what kinds of

assessments are used for measuring subthreshold ADHD

among children and adolescents. The results of the 18

articles included show that different definitions of sub-

threshold ADHD in children and adolescents exist, a large

variety of instruments are used, the prevalence rate of

subthreshold ADHD is wide-ranging (0.8–23.1 %), the

comorbidity of subthreshold ADHD is high and there are

several areas where subthreshold ADHD has a meaningful

impact on functioning. All these suggest that focusing on

subthreshold ADHD can be important in preventative

interventions. The results of this systematic review support

the dimensional approach of ADHD. Further research on

uniform criteria of subthreshold ADHD is needed to sup-

port the inclusion of this condition in classification

systems.

Keywords Attention-deficit/hyperactivity disorder �ADHD � Subthreshold � Subsyndromal � Subclinical �Prevention

Background

There is an ongoing debate in the literature as to whether a

categorical or a dimensional approach to psychiatric dis-

orders should be used [1, 2]. Classification systems such as

the Diagnostic and Statistic Manual for Mental Disorders

Third Revised (DSM-III-R) [3] and Fourth Edition (DSM-

IV) [4] and the International Classification of Diseases

Tenth Edition (ICD-10) [5], on which clinical work and

research have been based on so far, and even DSM-5 [6],

which has just been published, rely mainly on a categorical

approach, but both clinicians and researchers feel the need

to introduce a dimensional approach to the assessment of

psychiatric symptoms.

Implementing subthreshold forms of psychopathology

into classification systems as a hybrid of the categorical

and dimensional approaches could resolve the debate [7].

Conditions with relevant psychiatric symptoms which do

not meet the full criteria of a disorder according to the

classification systems are referred to as subthreshold

J. Balazs (&) � A. Kereszteny

Institute of Psychology, Eotvos Lorand University,

Izabella u. 46, Budapest 1064, Hungary

e-mail: [email protected]

J. Balazs

Vadaskert Child and Adolescent Psychiatry Hospital,

H}uvosvolgyi ut 116, Budapest 1021, Hungary

A. Kereszteny

School of Ph.D. Studies, Semmelweis University, Ull}oi ut 26,

Budapest 1086, Hungary

123

Eur Child Adolesc Psychiatry

DOI 10.1007/s00787-013-0514-7

disorders. Among children the greatest focus has been on

subthreshold depression and the results show that in spite

of the fact that there is no universally accepted definition of

subthreshold depression there is a high prevalence of this

condition among adolescents, which has a negative impact

on quality of life (QoL) and can be a precursor of later

major depressive episodes. Therefore, adolescents with

subthreshold depression should be the focus of preventative

interventions [7].

Attention-deficit/hyperactivity disorder (ADHD) is one

of the most prevalent (2–12 %) psychiatric disorders

among children and adolescents [8, 9]. The core symptoms

of ADHD are inattention, hyperactivity and impulsivity [3–

6]. According to the DSM-III-R the diagnosis of ADHD

requires the presence of 8 out of 14 specified inattention or

hyperactivity/impulsivity symptoms [3], whereas accord-

ing to the DSM-IV the diagnosis of ADHD requires either

the presence of six out of nine specified inattention

symptoms or six out of nine specified hyperactivity/

impulsivity symptoms [4]. The ICD-10 applies a stricter

criterion: at least six of the nine inattention symptoms and

three of the five hyperactivity symptoms and one of the

four impulsivity symptoms are required for the diagnosis of

hyperkinetic disorder [5]. The symptoms have to be present

for at least 6 months, have to cause impairment in at least

two settings and have to develop before the age of seven [4,

5]. The recently published DSM-5 contains a few differ-

ences from DSM-IV: above the age of 17 only five

symptoms are required out of the nine symptoms of inat-

tention or hyperactivity/impulsivity and several symptoms

must be present before the age of 12 instead of the age of

seven [6]. Though it is not included among the criteria of

the classification systems several studies highlight that

ADHD seriously compromises QoL of children and ado-

lescents [10, 11]. It is also well known that there is at least

one comorbid psychiatric diagnosis in more than two-thirds

of ADHD cases, which can be both externalisation and/or

internalisation disorders [12–14].

This article aims to present a review of subthreshold

ADHD among children and adolescents with a focus on the

following topics:

1. What is the prevalence of subthreshold ADHD among

children and adolescents?

2. What have researches found on the comorbidity of

subthreshold ADHD?

3. Is there already any impact of subthreshold ADHD on

functioning?

To be able to compare the included studies, before

answering the above questions we investigated the fol-

lowing: (1) what kinds of definitions of child and adoles-

cent subthreshold ADHD are used? (2) What kinds of

assessments are used for measuring subthreshold ADHD

among children and adolescents?

Methods

Selection of publications

A systematic literature search was conducted on the fol-

lowing five computerised literature databases on 30 May

2013: Ovid MEDLINE, Psychinfo, PubMed, Scopus, Web

of Science. Search terms from two categories were used:

(1) subclinical; subsyndromal; subthreshold and (2)

ADHD. Search terms within both categories were sepa-

rated by the Boolean operator OR, and categories were

separated by the operator AND. Using prespecified inclu-

sion and exclusion criteria we screened titles and/or

abstracts. The relevant full texts of papers passing the first

search were read and the ones that met the inclusion cri-

teria were collected. Reference lists of retrieved papers

were screened, and papers that possibly met the inclusion

criteria were retrieved and studied. Inclusion criteria were

as follows: studies with participants aged 18 and under

18 years at intake who had experienced subthreshold

ADHD, and a focus on at least one of the above-described

study questions; studies with clear-cut criteria/definitions

of subthreshold ADHD; peer-reviewed journals; publica-

tions written in English. The exclusion criterion was the

lack of any empirical data.

Results

Included studies

The search strategy resulted in a total of 669 articles

(including duplicates) of which 18 were included in the

systematic review after the screening process (Fig. 1;

Table 1).

Nine of the eighteen studies were performed in North

America [15–23], four in Europe [24–27], one in New-

Zealand [28] and four in Asia [29–32].

Of the 18 relevant publications, 11 had a cross-sectional

design [15, 19–22, 24, 26, 27, 29, 30, 32], and seven were

based on prospective longitudinal measures [16–18, 23, 25,

28, 31].

Fifteen studies were community based from the 18

included ones [15, 17–29, 32], while three studies had

clinical study groups [16, 30, 31].

The age of subjects at the time of cross-sectional studies

or at the beginning of longitudinal studies could be divided

into the following groups: one paper investigated children


123

under six as well [17], 11 examined children between 6 and

12 as well [15, 16, 19, 21, 22, 24, 25, 29–32], and six

focused only on adolescents aged 13–18 years old [18, 20,

23, 26–28].

Based on the method section of the included studies, in

the case of four included articles, two–two articles were

derived from the same studies [17, 18], [26, 27], but the

two–two articles had different study questions.

Definitions of subthreshold ADHD in the included

studies

In the included studies subthreshold ADHD was defined as

(see Table 1)

(1) having at least a minimum number of DSM-III-R or

DSM-IV symptoms for inattention and/or hyperac-

tivity, but not reaching full-symptom criteria,

(2) having at least a minimum number of DSM-IV

symptoms for inattention and/or hyperactivity, but not

reaching full DSM-IV symptom criteria and having

additional criteria,

(3) reaching full DSM-IV symptoms criteria, but not

other additional DSM-IV criteria or the symptom

criteria were reached in a certain way,

(4) elevated scores on a self-reported measure.

In the first three groups the presence of an elevated

number of symptoms of ADHD according to a categorical

structured interview was a necessary criterion, and in the

fourth group an elevated score on a dimensional measure

was the defined criterion.

(1) Eleven of the eighteen articles belong to this group

[16–20, 22–25, 28, 31]. Of these 11 articles five

applied the DSM-III-R criteria [19, 20, 22, 23, 25]:

three of them required from five to seven symptoms

of ADHD of the 14 possible symptoms [20, 23, 25],

Cukrowicz et al. [19] required one or two symptoms

short of a diagnosis according to the DSM-III-R, and

Scahill et al. [22] defined subthreshold ADHD as a

score of 13–19 on the ADHD module of the DISC-R,

which means more than six and fewer than ten

symptoms of ADHD (see Table 1). Of the six articles

which used the DSM-IV systems for symptom

criteria, one paper required only one symptom of

ADHD for subthreshold diagnosis [28], two studies

required more than three symptoms [16, 31], two

studies required four or five symptoms [17, 18],

and one study required five symptoms [24] (see

Table 1).

(2) In two papers a minimum–maximum symptom crite-

rion was required as it was in the first group of papers:

three to five inattentive and/or hyperactive/impulsive

symptoms had to be present; additionally some

impairment caused by the symptoms should be

present in two or more settings; and children also

had to fulfil DSM-IV ADHD age-of-onset criteria [29,

32] (see Table 1).

(3) Three studies of the eighteen required the full DSM-

IV symptoms criteria, but additional criteria of the

diagnosis of ADHD were not required: in Gau et al.

[31] either the symptoms do not cause any impair-

ment, or either other or youth K-SADS-E interviews,

but not both, reached the symptom criteria of ADHD,

whereas in Malmberg et al. [26, 27] six of nine

symptoms for ADHD-inattentive and at least six of

nine symptoms for ADHD-hyperactive were fulfilled,

but at least one actual symptom was assessed as

‘possible’ according to K-SADS-PL (threshold diag-

nosis would have included only ‘certain’ symptoms in

this study) (see Table 1).

(4) Two of the eighteen papers defined subthreshold

ADHD as having elevated scores on a self-reported

measure [15, 21]: August et al. [15] required C60 on

CBCL-TRF and \65 T score on the Hyperactivity

scale on the CBCL-PRF, whereas Rielly et al. [21]

required scoring at or above the 85th percentile on the

CBCL Self-rated Attention Problems scale (see

Table 1).

Potentially Relevant Studies Identified and Screened for Retrieval

including duplicates N = 669

Studies excluded after reading title and abstract

Not subthreshold ADHD = 142 Not children = 34

Not empirical study = 5

Studies Retrieved for more detailed evaluation

N = 66

Studies excluded after reading paper Not subthreshold ADHD = 16

Not children = 3 Not empirical study = 13

Not English = 1 Not focus on review questions = 14

Not peer-reviewed = 1

Studies Included in the Systematic Review N = 18

Potentially Relevant Studies Identified and Screened for Retrieval

after excluding duplicates N = 247

Fig. 1 QUOROM flow chart detailing results of literature search


123

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123

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5y

ears

Co

nce

rnin

gfu

nct

ion

ing

tho

sem

eeti

ng

crit

eria

for

full

syn

dro

me

AD

HD

had

the

wo

rst

ou

tco

mes

,th

ose

wit

hn

osy

mp

tom

sh

ad

the

bes

to

utc

om

es,

and

tho

sew

ith

sub

thre

sho

ld

AD

HD

had

ou

tco

mes

that

wer

ein

term

edia

te

bet

wee

nth

eo

ther

two

gro

up

s

Gau

etal

.

[30

]

Tai

wan

Cro

ss-

sect

ion

al

Cli

nic

al

sam

ple

,

sch

oo

l

con

tro

ls

K-S

AD

S-E

Tw

oco

nd

itio

ns

wer

e

cate

go

rize

das

sub

thre

sho

ldA

DH

D:

(1)

eith

erm

oth

ero

ry

ou

th

K-S

AD

S-E

inte

rvie

ws,

bu

t

no

tb

oth

,re

ach

edd

efin

ite

AD

HD

atad

ole

scen

cean

d

(2)

bo

thre

ach

edp

oss

ible

or

pro

bab

leA

DH

D:

pro

bab

le(e

ith

ern

ot

reac

hin

gfu

llD

SM

-IV

sym

pto

ms

crit

eria

bu

t

mo

reth

anh

alf

or

no

fun

ctio

nal

imp

airm

ent)

,

po

ssib

le(s

om

esy

mp

tom

s

bu

tn

oim

pai

rmen

t)

Ad

ole

scen

tsag

ed1

1–

17

,

wh

ow

ere

dia

gn

ose

dw

ith

AD

HD

,ac

cord

ing

to

DS

M-I

Vcr

iter

ia,

atth

e

mea

nag

eo

f6

.7y

ears

(SD

3.0

):2

81

(24

0b

oy

s;

14

5w

ith

per

sist

ent

AD

HD

,1

36

wit

h

sub

thre

sho

ldA

DH

D);

un

affe

cted

con

tro

l

sub

ject

s:1

85

11

–1

7y

ears

:

Per

sist

ent

AD

HD

:

mea

nag

e1

2.8

(SD

1.5

)

Su

bth

resh

old

AD

HD

:m

ean

age

12

.9(S

D1

.6)

Co

ntr

ol

sub

ject

s:

mea

nag

e1

2.9

(SD

1.5

)

Th

est

ud

yfo

un

dan

asso

ciat

ion

bet

wee

n

AD

HD

and

slee

p

pro

ble

ms,

wh

ich

can

be

par

tial

lyex

pla

ined

by

the

psy

chia

tric

com

orb

idit

ies.

Ho

wev

er,

the

resu

lts

did

no

tsu

pp

ort

ad

istu

rbed

slee

psc

hed

ule

.T

he

auth

ors

reco

mm

end

that

men

tal

hea

lth

pro

fess

ion

als

sho

uld

scre

enfo

rsl

eep

pro

ble

ms

and

psy

chia

tric

com

orb

idit

ies

amo

ng

ado

lesc

ents

wit

ha

chil

dh

oo

dd

iag

no

sis

of

AD

HD

reg

ard

less

of

the

sev

erit

yo

fcu

rren

tA

DH

D

sym

pto

ms


123

Ta

ble

1co

nti

nu

ed

Ref

eren

ceC

ou

ntr

yS

tud

yd

esig

nS

amp

leM

easu

res

Defi

nit

ion

of

sub

thre

sho

ld

AD

HD

Po

pu

lati

on

ato

nse

tP

op

ula

tio

n’s

age

at

on

set

Mai

nfi

nd

ing

s

Gau

etal

.

[31

]T

aiw

anL

on

git

ud

inal

:

6y

ears

Cli

nic

al

sam

ple

,

sch

oo

l

con

tro

ls

K-S

AD

S-E

Mo

reth

anh

alf

of

the

DS

M-

IVsy

mp

tom

s,w

hic

har

e

req

uir

edfo

rfu

llD

SM

-IV

dia

gn

ost

iccr

iter

ia

Pat

ien

tsag

ed1

1–

16

,w

ho

wer

ecl

inic

ally

dia

gn

ose

d

wit

hA

DH

Dat

the

mea

n

age

of

7.3

?2

.8y

ears

:

93

chil

dre

n(7

7b

oy

s)

Ag

e-,

sex

-,an

dp

aren

tal

edu

cati

on

-mat

ched

sch

oo

l

con

tro

ls:

93

chil

dre

n

11

–1

6y

ears

Cli

nic

alsa

mp

le:

mea

nag

e

13

.2y

ears

(SD

1.5

)

Co

ntr

ol

sam

ple

:

mea

nag

e

13

.3y

ears

(SD

1.4

)

Pro

fess

ion

als

sho

uld

care

full

yre

-ass

ess

AD

HD

sym

pto

ms

and

psy

chia

tric

com

orb

idit

y

amo

ng

ado

lesc

ents

wit

ha

chil

dh

oo

dd

iag

no

sis

of

AD

HD

bec

ause

of

the

per

sist

ence

of

AD

HD

,th

e

chan

ges

of

AD

HD

sub

typ

es,

and

the

hig

h

psy

chia

tric

com

orb

idit

y

atad

ole

scen

ce

Th

est

ud

ysu

gg

ests

that

bo

thm

ater

nal

and

chil

d

rep

ort

sar

eim

po

rtan

tto

mak

eth

ed

iag

no

sis

of

AD

HD

Kad

esjo

and

Gil

lber

g

[25

]

Sw

eden

Lo

ng

itu

din

al:

4y

ears

T1

T2

:2

yea

rs

late

r

T2

:4

yea

rs

late

r

Co

mm

un

ity

sam

ple

Tea

cher

qu

esti

on

nai

re

scre

enin

g,

teac

her

inte

rvie

w,

bri

ef

Co

nn

er’s

(10

-

item

)

qu

esti

on

nai

re,

Co

nn

er’s

par

ent

beh

avio

ura

l

foll

ow

-up

5,

6,

or

7o

fth

e1

4D

SM

-III

-

RA

DH

Dcr

iter

ia

40

9ch

ild

ren

(22

4b

oy

s):

AD

HD

:1

5ch

ild

ren

Su

bth

resh

old

AD

HD

:4

2

chil

dre

n

No

AD

HD

:3

52

chil

dre

n

At

bas

elin

e:

7-y

ear-

old

s

Th

era

teo

fco

mo

rbid

ity

in

sub

thre

sho

ldA

DH

Dw

as

fou

nd

tob

ev

ery

hig

h.

Kim

etal

.

[32

]

So

uth

Ko

rea

Cro

ss-

sect

ion

al

Co

mm

un

ity

sam

ple

DIS

C-I

V3

–5

inat

ten

tiv

ean

d/o

r

hy

per

acti

ve/

imp

uls

ive

sym

pto

ms.

Ch

ild

ren

also

had

tofu

lfill

DS

M-I

V

AD

HD

age-

of-

on

set

and

imp

airm

ent

crit

eria

to

qu

alif

yfo

ra

dia

gn

osi

so

f

sub

thre

sho

ldA

DH

D

2,6

73

stu

den

ts:

AD

HD

:1

23

chil

dre

n

Su

bth

resh

old

-AD

HD

:2

31

chil

dre

n

No

n-A

DH

D:

2,3

19

chil

dre

n

AD

HD

:m

ean

age

10

.0y

ears

(SD

2.9

)

Su

bth

resh

old

-

AD

HD

:m

ean

age

10

.9y

ears

(SD

3.0

)

No

n-A

DH

D:

mea

n

age

11

.2y

ears

(SD

3.1

)

Th

e1

-yea

rp

rev

alen

cera

te

for

sub

thre

sho

ldA

DH

D

was

8.6

%

Th

ere

wer

esi

gn

ifica

ntl

y

mo

reco

mo

rbid

anx

iety

,

mo

od

,o

pp

osi

tio

nal

defi

ant,

con

du

ct,

and

tic

dis

ord

ers

inch

ild

ren

wit

h

bo

thfu

llsy

nd

rom

ean

d

sub

thre

sho

ldA

DH

Dth

an

inth

eco

ntr

ol

gro

up


123

Ta

ble

1co

nti

nu

ed

Ref

eren

ceC

ou

ntr

yS

tud

yd

esig

nS

amp

leM

easu

res

Defi

nit

ion

of

sub

thre

sho

ld

AD

HD

Po

pu

lati

on

ato

nse

tP

op

ula

tio

n’s

age

at

on

set

Mai

nfi

nd

ing

s

Lew

inso

hn

etal

.[2

0]

US

AC

ross

-

sect

ion

al

Co

mm

un

ity

sam

ple

K-S

AD

SS

ub

thre

sho

ldA

DH

Dis

defi

ned

ash

avin

gfi

ve

or

mo

resy

mp

tom

san

dn

ever

mee

tin

gth

efu

llA

DH

D

acco

rdin

gto

DS

M-I

II-R

1,7

04

ado

lesc

ents

(47

.9%

bo

ys)

Stu

den

tsin

gra

des

9–

12

;m

ean

age

16

.6y

ears

(SD

1.2

)

Th

ep

rev

alen

ceo

f

sub

thre

sho

ldA

DH

Dw

as

6.4

%

Ch

ild

ren

wit

hsu

bth

resh

old

AD

HD

had

sig

nifi

can

tly

incr

ease

dp

rob

abil

ity

of

the

foll

ow

ing

dis

ord

ers:

maj

or

dep

ress

ive

dis

ord

er,

OR

2.9

(1.6

–5

.0),

alco

ho

l

dep

end

ence

,O

R2

.5

(1.1

–6

.1),

con

du

ct

dis

ord

er,

OR

4.7

(2.0

–1

1.4

)

Mal

mb

erg

etal

.[2

6]

Sw

eden

Cro

ss-

sect

ion

al

Co

mm

un

ity

sam

ple

K-S

AD

S-P

LT

he

sub

thre

sho

ldd

iag

no

ses

wer

eb

ased

on

the

dia

gn

ost

iccr

iter

iao

fth

e

DS

M-I

VT

R.

Su

bth

resh

old

AD

HD

:th

e

ado

lesc

ents

wer

ere

gar

ded

ash

avin

ga

cert

ain

sym

pto

mif

the

actu

al

sym

pto

mw

asas

sess

edas

‘po

ssib

le’

or

‘cer

tain

’

acco

rdin

gto

K-S

AD

S-P

L.

At

leas

tsi

xo

fn

ine

sym

pto

ms

for

AD

HD

-

inat

ten

tiv

ean

dat

leas

tsi

x

of

nin

esy

mp

tom

sfo

r

AD

HD

-hy

per

acti

ve

wer

e

fulfi

lled

,b

ut

atle

ast

on

e

actu

alsy

mp

tom

was

asse

ssed

as‘p

oss

ible

’an

d

no

t‘c

erta

in’

acco

rdin

gto

K-S

AD

S-P

L

Th

resh

old

AD

HD

:

thre

sho

ldd

iag

no

sis

wo

uld

hav

ein

clu

ded

on

ly

‘cer

tain

’sy

mp

tom

s

Th

ep

op

ula

tio

n-b

ased

Sw

edis

htw

inst

ud

yo

f

chil

dan

dad

ole

scen

t

dev

elo

pm

ent

(TC

HA

D)

(th

eau

tho

rsu

sen

otw

in

met

ho

do

log

yin

this

pap

er):

17

7g

irls

and

13

5b

oy

s:

Su

bth

resh

old

AD

HD

:2

9

Su

bth

resh

old

beh

avio

ur

dis

ord

er:

31

No

dia

gn

osi

s:2

52

Mea

nag

e

16

yea

rs,

ran

gin

g

fro

m1

4.6

to

16

.7y

ears

Th

ep

rev

alen

ceo

f

sub

thre

sho

ldA

DH

Dw

as

asfo

llo

w:

AD

HD

inat

ten

tiv

ety

pe:

23

.1%

,

AD

HD

hy

per

acti

ve/

imp

uls

ive

typ

e:1

5.0

%,

AD

HD

com

bin

edty

pe:

9.5

%

Th

ech

ild

ren

glo

bal

asse

ssm

ent

scal

esc

ore

s

wer

esi

gn

ifica

ntl

ylo

wer

inch

ild

ren

wit

hea

ch

sub

typ

esu

bth

resh

old

AD

HD

and

wit

hea

ch

sub

typ

efu

llsy

nd

rom

e

AD

HD

than

inch

ild

ren

wit

ho

ut

such

dia

gn

osi

s


123

Ta

ble

1co

nti

nu

ed

Ref

eren

ceC

ou

ntr

yS

tud

yd

esig

nS

amp

leM

easu

res

Defi

nit

ion

of

sub

thre

sho

ld

AD

HD

Po

pu

lati

on

ato

nse

tP

op

ula

tio

n’s

age

at

on

set

Mai

nfi

nd

ing

s

Mal

mb

erg

etal

.[2

7]

Sw

eden

Cro

ss-

sect

ion

al

Co

mm

un

ity

sam

ple

K-S

AD

S-P

LT

he

sub

thre

sho

ldd

iag

no

ses

wer

eb

ased

on

the

dia

gn

ost

iccr

iter

iao

fth

e

DS

M-I

VT

R.

Su

bth

resh

old

AD

HD

:th

ead

ole

scen

ts

wer

ere

gar

ded

ash

avin

ga

cert

ain

sym

pto

mif

the

actu

alsy

mp

tom

was

asse

ssed

as‘p

oss

ible

’o

r

‘cer

tain

’ac

cord

ing

to

K-S

AD

S-P

L.

At

leas

tsi

x

of

nin

esy

mp

tom

sfo

r

AD

HD

-in

atte

nti

ve

and

at

leas

tsi

xo

fn

ine

sym

pto

ms

for

AD

HD

-hy

per

acti

ve

wer

efu

lfill

ed,

bu

tat

leas

t

on

eac

tual

sym

pto

mw

as

asse

ssed

as‘p

oss

ible

’an

d

no

t‘c

erta

in’

acco

rdin

gto

K-S

AD

S-P

L

Th

resh

old

AD

HD

:

thre

sho

ldd

iag

no

sis

wo

uld

hav

ein

clu

ded

on

ly

‘cer

tain

’sy

mp

tom

s

Th

ep

op

ula

tio

n-b

ased

Sw

edis

htw

inst

ud

yo

f

chil

dan

dad

ole

scen

t

dev

elo

pm

ent

(TC

HA

D)

(th

eau

tho

rsu

sen

otw

in

met

ho

do

log

yin

this

pap

er):

17

7g

irls

and

13

5b

oy

s:

Su

bth

resh

old

AD

HD

:2

9

Su

bth

resh

old

beh

avio

ur

dis

ord

er:

31

No

dia

gn

osi

s:2

52

Mea

nag

e

16

yea

rs,

ran

gin

g

fro

m1

4.6

to

16

.7y

ears

Su

bth

resh

old

AD

HD

was

risk

fact

ors

for

sev

eral

oth

erp

sych

iatr

ic

sym

pto

ms,

e.g

.sm

ok

ing

and

hig

hal

coh

ol

con

sum

pti

on

.In

gir

ls,

sub

thre

sho

ldA

DH

D

coex

iste

dw

ith

the

scre

enin

gq

ues

tio

ns

of

dep

ress

ion

,m

ania

,p

anic

atta

ck,

ph

ob

ias,

ano

rex

ia

ner

vo

sa,

mo

tor

tics

and

po

sttr

aum

atic

stre

ss

dis

ord

er.

Inb

oy

s,

sub

thre

sho

ldA

DH

Dw

as

asso

ciat

edw

ith

dep

ress

ion

and

PT

SD

Rie

lly

etal

.

[21

]

Can

ada

Cro

ss-

sect

ion

al

Co

mm

un

ity

sam

ple

CB

CL

-stu

den

ts,

CB

CL

-par

ents

,

CB

CL

-tea

cher

s,

AD

HD

sym

pto

m

rati

ng

sfr

om

the

DS

M-I

V

Ch

ild

ren

wit

hsu

bth

resh

old

atte

nti

on

pro

ble

ms:

sco

rin

g

ato

rab

ov

eth

e8

5th

per

cen

tile

on

the

CB

CL

self

rate

dat

ten

tio

n

pro

ble

ms

scal

e

Co

mp

aris

on

stu

den

ts

wit

ho

ut

atte

nti

on

pro

ble

ms:

cori

ng

bel

ow

the

50

thp

erce

nti

leo

nth

is

mea

sure

Su

bth

resh

old

atte

nti

on

pro

ble

mg

rou

p:

64

chil

dre

n(3

4b

oy

s)

Co

mp

aris

on

gro

up

:8

5

chil

dre

n(3

0b

oy

s)

Mea

nag

e1

1.8

(SD

1.2

,ra

ng

e

10

–1

4y

ears

)

Ch

ild

ren

wit

hsu

bth

resh

old

atte

nti

on

pro

ble

ms

had

mo

red

iffi

cult

ies

than

con

tro

lsac

ross

the

soci

al

do

mai

ns

of

fun

ctio

nin

g


123

Ta

ble

1co

nti

nu

ed

Ref

eren

ceC

ou

ntr

yS

tud

yd

esig

nS

amp

leM

easu

res

Defi

nit

ion

of

sub

thre

sho

ld

AD

HD

Po

pu

lati

on

ato

nse

tP

op

ula

tio

n’s

age

at

on

set

Mai

nfi

nd

ing

s

Sca

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123

Assessment of subthreshold ADHD in the included

studies

Diagnostic interviews and parent-, teacher- and self-rated

questionnaires were used in the 18 publications to assess

subthreshold ADHD. Only diagnostic interviews were used

in nine of the 18 publications [16, 19, 20, 23, 26, 27, 30–

32]. Both diagnostic interviews and a rating questionnaire

(parent/teacher/self) were used in six papers [15, 17, 18,

22, 28, 29]. Only rating questionnaires were used in three

papers [21, 24, 25] (see Table 1).

The most commonly used structured diagnostic inter-

view was the Schedule for Affective Disorder and

Schizophrenia for School-Age Children (K-SADS) [33,

34], which was used in nine papers [16–18, 20, 23, 26, 27,

30, 31]. The Diagnostic Interview Schedule for Children,

Version (DISC) [35], was used in 6 of the 18 papers [17,

18, 21, 28, 29, 32]. Among rating scales the Children’s

Behavior Checklist (CBCL) [36] was the most commonly

used, in three papers [15, 21, 28], whereas Conners’s

Rating Scales [37] and ADHD Rating Scales [38] were

used in two–two studies [22, 25], [21, 29] (see Table 1).

Review questions on subthreshold ADHD in children

and adolescents

Prevalence of subthreshold ADHD in children

and adolescents

When we look at the reported prevalence data on sub-

threshold ADHD, we have to take into account, as we said

above, that in the included articles there are differences in

the definitions of subthreshold ADHD, in the measures and

the source of information and in the origin of the sample

(community versus clinical). Of the included 18 papers six

reported data on the prevalence of subthreshold ADHD

[19, 20, 24, 26, 29, 32]. In all studies [19, 20, 26, 29, 32],

except one, where a parent-rated questionnaire was used

[24], a structured diagnostic interview was applied to

measure subthreshold ADHD. The point prevalence of

subthreshold ADHD ranged from 0.8 to 23.1 %.

Cukrowicz et al. [19], using a structured diagnostic

interview (DICA-R), defined subthreshold ADHD as having

one or two symptoms short of a diagnosis according to the

DSM-III-R in the 11-year-old age group and found 1.0 %

for subthreshold ADHD, whereas among 17-year-olds the

prevalence rate was 0.8 %. Airaksinen et al. [24] defined

subthreshold ADHD as having 5 of the 9 DSM-IV items for

inattention and/or hyperactivity and used a parent-rated

questionnaire (FTF): they found in the 6- to 8-year-old age

group a 1.9 % prevalence rate for subthreshold ADHD.

Cho et al. [29] defined subthreshold ADHD as having

three to five symptoms of the nine DSM-IV items for

inattention and/or hyperactivity and required children to

have impairment as well; using a structured diagnostic

interview (DISC-IV) for the 9.0 (±1.7) age group they

found a 9–11.7 % prevalence rate. Kim et al. [32] applied

the same definition and instruments in the 10.9 (3.0) age

group and found a prevalence rate of 8.64 %.

Lewinsohn et al. [20] defined subthreshold ADHD as

having five or more symptoms of the 14 DSM-III-R items

for inattention and/or hyperactivity and never meeting the

full ADHD according to DSM-III-R; using a structured

diagnostic interview (K-SADS) in the 16.6 (SD 1.2 years)

age group they found a 6.4 % prevalence rate.

Malmberg et al. [26], examining 14.6- to 16.7-year-old

adolescents with a structured interview and requiring six of

nine symptoms (but certain symptoms received a ‘possible’

and not ‘certain’ rating), found the highest prevalence rate:

ADHD inattentive type 23.1 %, ADHD hyperactive/

impulsive type 15.0 % and ADHD combined type 9.5 %.

Further two studies focused on the prevalence of sub-

threshold ADHD developed from full-syndrome ADHD,

when people with ADHD no longer met full DSM-IV

criteria for ADHD, but had subthreshold ADHD [16, 31].

Gau et al. [31] found in their 6-year follow-up that 33.3 %

of those with childhood diagnosis of ADHD no longer met

full DSM-IV criteria for ADHD, but had subthreshold

ADHD, and in their 10-year longitudinal study Biederman

et al. [16] reported that 22 % of those children who were

previously diagnosed with ADHD had subthreshold

ADHD. These two studies used the same definition for

subthreshold ADHD.

Comorbidity of subthreshold ADHD in children

and adolescents

Nine papers reported comorbidity data next to subthreshold

ADHD, and all of them found it to be highly prevalent;

some 12–70 % of people with subthreshold ADHD had at

least one comorbid disorder [15, 20, 22, 24, 25, 27, 30–32].

August et al. [15] and Scahill et al. [22] observed that

the comorbidity next to the subthreshold ADHD is signif-

icantly lower than it is known in full-syndrome ADHD. In

contrast, Kadesjo and Gillberg [25] found a higher

comorbidity rate in subthreshold ADHD than in full-syn-

drome ADHD. Kim et al. [32] reported that children with

both subthreshold and full-syndrome ADHD had signifi-

cantly higher comorbidity of oppositional defiant disorder,

conduct disorder, mood disorder, anxiety disorder and tic

disorder than controls and the comorbidity rate was not

significantly different between full-syndrome and sub-

threshold ADHD, except for anxiety disorders, which was

higher in full-syndrome ADHD. According to August et al.

[15] subthreshold ADHD was significantly associated with

externalising disorders, such as oppositional defiant


123

disorder and conduct disorder, but not with internalising

disorders. Lewinsohn et al. [20] found that subthreshold

ADHD was significantly associated with major depressive

disorder, alcohol dependence and conduct disorder.

Malmberg et al. [27] suggested that subthreshold ADHD is

a risk factor for several other psychiatric symptoms as well

as smoking and high alcohol consumption. In girls, sub-

threshold ADHD was comorbid with depression, mania,

panic attack, phobias, anorexia nervosa, motor tics and

posttraumatic stress disorder (PTSD), and in boys with

depression and PTSD. Gau et al. [30] highlight the

importance of sleep problems next to subthreshold ADHD.

Taking the role of age into account when investigating

comorbidity, August et al. [15] who examined children

from 1 to 4 grades found no association between sub-

threshold ADHD and internalizing disorders. Kim et al.

[32] enrolled children with mean age 10.9 years (SD 3.0)

found higher comorbidity of internalizing disorder in

children with subthreshold ADHD than in the control

group.

Two additional studies did not investigate the comor-

bidity of subthreshold ADHD, but whether subthreshold

ADHD at a certain age predicts the presence of other dis-

orders later. In their 15-year longitudinal study Shankman

et al. [23] found that subthreshold ADHD, when compared

with those who had neither subthreshold ADHD nor full-

syndrome ADHD, significantly predicted a first onset of

full-syndrome alcohol dependence, substance use disorder,

and conduct disorder/antisocial personality disorder. Con-

cerning ODD and depression/anxiety, in their 8-year fol-

low-up study Bussing et al. [17] found that compared with

the control group only those with childhood ADHD, but

not with subthreshold ADHD, had significantly increased

odds of these disorders.

Impact of subthreshold ADHD on functioning in children

and adolescents

Overall, the reviewed literature on the impact of sub-

threshold ADHD on functioning describes several areas

which need attention [15, 17, 18, 21, 22, 26, 28].

August et al. [15] reported that children with sub-

threshold ADHD obtained higher achievement scores for

each investigated academic domain (reading, writing, lan-

guage and maths) than did children with ADHD.

Bussing et al. [17, 18] reported in their follow-up studies

(8 and 10 years) that subthreshold ADHD significantly

increased the risk of grade retention (OR 6.1, CI 2.7–13.5)

and graduation failure (OR 11.2, CI 2.7–47.3) compared

with controls. Full-syndrome ADHD significantly

increased the risk of graduation failure (OR 5.2, CI

1.3–21.6), but not of grade retention (OR 1.4, CI 0.6–3.4).

Bussing et al. [17] found, however, that parents and

adolescents reported more functional impairment and

lower QoL for children with ADHD than children with

subthreshold or no ADHD.

Fergusson et al. [28] examined the association between

increasing severity of ADHD (i.e. non-ADHD, subthresh-

old ADHD, full-syndrome ADHD) and later outcomes,

including getting pregnant or getting partner pregnant by

the age of 20; becoming a parent by the age of 20; leaving

school without qualifications; having university degree up

to the age of 25. They found that children with full-syn-

drome ADHD showed the worst outcomes (33.8, 21.6,

53.6, 7.3 %, respectively), non-ADHD children showed the

best rates (9.5, 3.6, 6.0, 39.2 %, respectively) and children

with subthreshold ADHD had intermediate outcomes (19.2,

8.6, 21.7, 20.7 %, respectively) (in all cases: linear trend

p \ 0.001).

Malmberg et al. [26] found that the scores of the Chil-

dren Global Assessment Scale (CGAS) were significantly

lower in children with subthreshold and with full-syndrome

ADHD compared with controls.

Scahill et al. [22] reported that the CGAS score of the

ADHD group showed significantly greater overall impair-

ment than the subthreshold ADHD group and the sub-

threshold ADHD group showed significantly greater

overall impairment than the control group. Family dys-

function was significantly greater in the ADHD group

compared with the subthreshold and the non-ADHD group;

here the subthreshold ADHD group showed no significant

difference compared with the controls.

Rielly et al. [21] reported that children with subthresh-

old attention problems had fewer friends, more negative

reputations and reported lower levels of friendship quality

than controls.

Discussion

Systematically searching the literature, we found different

definitions of subthreshold ADHD in children and adoles-

cents as seen in the case of adolescent subthreshold

depression [7]. The majority of the studies required at least

a minimum number of symptoms for inattention and/or

hyperactivity, but not full-symptom criteria of the classi-

fication systems [16–20, 22–25, 28–30, 32]. Only a few

studies required additional criteria next to the presence of a

minimum number of symptoms, like the presence of

functional impairment and age-onset criteria [29, 32].

Within those studies where a symptom criterion was

required, we found notable differences. Some studies

applied less stringent requirements, i.e. the presence of one

to three symptoms of ADHD was enough for the definition

of subthreshold ADHD (e.g. [28, 16, 30]), whereas other

studies required the presence of more symptoms (four or


123

five) [17, 18, 24]. An interesting group of studies required

the full-symptom criteria of the classification systems, but

either the symptoms did not cause functional impairment

[30] or even though the required number of symptoms was

present at least one of them was assessed as ‘possible’ (not

‘certain’) according to the interview [26, 27].

All the above-listed papers, where the definition of

subthreshold ADHD required a certain number of symp-

toms, used structured diagnostic interviews as a measure.

There are only two studies among the ones included in this

review where the diagnoses of subthreshold ADHD were

based on a self-reported measure: in these cases a defined

elevated score was required [15, 21].

On the basis of the results of the current review we

suggest, as Bertha and Balazs [7] did in their review

paper on adolescent subthreshold depression, that the

introduction of uniform research criteria for subthreshold

ADHD is necessary. To establish again a categorical

definition of subthreshold ADHD is a difficult issue while

it seems that this condition is dimensionally distributed in

the population. Based on the current review we still

cannot say the exact number of symptoms of subthresh-

old ADHD while as we describe later the impact of

subthreshold ADHD does not depend on the number of

symptoms. In this way further studies are needed to

clarify (if there is at all) a minimum number of symp-

toms (i.e. one or two or three or four or five) for inat-

tention and/or hyperactivity, for the definition of

subthreshold ADHD. Based on the current review the

definition of subthreshold ADHD may include that the

symptoms should cause functional impairment. In our

opinion the age criterion, which is now 12 years for

ADHD in the DSM-5 [6], is not a necessary criterion of

subthreshold ADHD, although it is important to recognise

cases with a certain number of symptoms and functional

impairment after this age as well.

Though in the recently published DSM-5 ‘‘Other Spec-

ified Attention-Deficit/Hyperactivity Disorder’’ and

‘‘Unspecified Attention-Deficit/Hyperactivity Disorder’’

are categories which apply ‘‘to presentations in which

symptoms characteristic of ADHD that cause clinically

significant distress or impairment in social, occupational or

other important areas of functioning predominate but do

not meet the full criteria for attention-deficit/hyperactivity

disorder’’ ([6], p 35), none of them provide a further clear,

uniform criteria with an exact number of symptoms, which

would be important both to clinicians and researchers to

build a common language.

Similarly to the literature on adolescent subthreshold

depression [7], the studies on subthreshold ADHD in

children and adolescents used a large variety of instru-

ments: the majority of the studies used diagnostic inter-

views, but we could find different ones [15–20, 22, 23, 26–

32]. Rating scales were the only instruments for measuring

subthreshold ADHD in three studies [21, 24, 25] and in

several studies these were complementary measures [15,

17, 18, 22, 28, 29]. For future research we suggest the use

of structured interviews and, as complementary measures,

self-report scales could be useful as well.

The prevalence rate of subthreshold ADHD was found

in a wide range (0.8–23.1 %) in the included studies. This

wide range can be partly explained by the above-described

different aspects of the studies on subthreshold ADHD,

such as definition and measurement. The lower figures

came from researches where the definition of subthreshold

ADHD required more symptoms (i.e. [19, 24]) and the

higher ones were found in researches where the definition

of subthreshold ADHD required fewer symptoms (i.e. [29,

32]). Malmberg et al. [26] found the highest prevalence

rate of adolescent subthreshold ADHD; though the authors

required the presence of most symptoms (six of the nine),

some of the symptoms should have been present only as

‘possibilities’. When we include the role of age of the study

sample additionally to the role of the definition of sub-

threshold ADHD in the prevalence rate of subthreshold

ADHD, we cannot find any specific association. As we

described above there is a great heterogeneity in definitions

which do not allow us to draw any conclusion regarding the

role of age in the prevalence rate of subthreshold ADHD. It

seems that in both children and adolescents we can find

lower and higher prevalence data depending on definition.

In the current review we could not investigate the role of

the origin of the sample (community versus clinical) while

there are only two included studies with clinical samples

which examine prevalence rate, but these ones focus on the

long-term outcome of ADHD. Even given the lower

prevalence rates of subthreshold ADHD, all these data

offer further evidence for the importance of clinical

screening and recognising children with subthreshold

ADHD. The wide range of the prevalence of subthreshold

ADHD in the included studies underlines the need for

further studies with a clear methodology.

Longitudinal studies focusing on people with childhood

ADHD who do not meet the criteria of full-syndrome

ADHD any longer but still have symptoms of ADHD

reported an important group of subthreshold ADHD: in

6 years one-third of those who had previously full-syn-

drome ADHD had subthreshold ADHD [32] and in

10 years only one-fifth of people with childhood ADHD

developed subthreshold ADHD [16]. All these results show

that psychiatrists need to reassess people with childhood

diagnosis of ADHD carefully and screen for subthreshold

ADHD.

All the included studies agreed that, similarly to full-

syndrome ADHD, subthreshold ADHD is also significantly

associated with comorbid psychiatric disorders [15, 20, 22,


123

24, 25, 27, 30–32]. Additionally, subthreshold ADHD

predicts several full-syndrome disorders, such as alcohol

and substance use disorders, conduct disorder and antiso-

cial personality disorder [23]. There are already differences

in the results of these studies, if the comorbidity rate next

to the subthreshold ADHD is the same, lower or higher

than it is in full-syndrome ADHD and if it is true for both

externalisation and internalisation disorders as well.

Reviewing whether comorbidity next to subthreshold

ADHD differs according to the definition of subthreshold

ADHD in the included studies, we could not find any

specific pattern. Investigating the influencing factor of age

on comorbidity the included studies suggest that in younger

age externalization disorders are already present as

comorbidity next to subthreshold ADHD, while internali-

zation disorders appear only in somewhat later age [15,

32]. Further studies with a clear methodology (i.e. uniform

research criteria for subthreshold ADHD) would answer

these questions. Nevertheless, the results of the current

review highlight the importance of assessing comorbidity

next to subthreshold ADHD.

The included studies highlight several areas where

subthreshold ADHD has a meaningful impact on func-

tioning: children with subthreshold ADHD have higher

levels of educational [17, 18, 28], functional [17, 22, 26]

and interpersonal impairments [21] and risk behaviour [28]

than children with no ADHD. Most of the studies on

subthreshold ADHD reached the conclusion that those

meeting criteria for full-syndrome ADHD had the worst

outcomes, those with no symptoms had the best outcomes

and those with subthreshold ADHD had intermediate out-

comes [15, 22, 28]. It was found both in children and

adolescents as well [15, 21, 22, 28]. In the included studies

both milder and stricter definitions of subthreshold ADHD

were associated with functional impairment [15, 17, 18, 21,

22, 26, 28].

All the results of the current review support the previous

conclusion [7] that focusing on subthreshold conditions,

including subthreshold ADHD, can be important in pre-

ventative interventions. Balazs and Bertha [7] suggested in

the case of subthreshold depression that both professional

and non-professionals working with children (e.g. school

staff) should adopt a screening programme to recognise the

symptoms of depression even at a subthreshold level. To

this end, educational programmes for non-healthcare pro-

fessionals and screening programmes should be developed.

Both professionals and stakeholders should support this

process. Our results highlight the clinical importance of

investigating adolescents with high level of ADHD

symptoms—which do not fulfil the diagnostic criteria of

the classification systems—in view of comorbidities and

functioning. Naturally it would increase the prevalence rate

of ADHD phenomenon (subthreshold and full-syndrome

disorder), as well as the number of children referred to

psychiatric care. It raises the danger of medicalization.

That is why it is important what we suggested above that

the definition of subthreshold ADHD should include

functional impairment. Another important issue is what

kind of treatment should be suggested for children/ado-

lescents with subthreshold ADHD. We definitely suggest

that pharmacological treatment should be kept for children

with full-syndrome ADHD. Further studies are needed to

investigate the effect (including improvement, ‘‘adverse

events’’ and cost-effectiveness) of non-pharmacological

treatment—i.e. psychoeducation, cognitive-behavior ther-

apy, trainings for parents and teachers—of subthreshold

ADHD. The higher number of children and adolescents

who are referred to psychiatric care due to the impairment

caused by the symptoms of subthreshold ADHD can lead to

a higher economical burden in short-term, but it can be

considered a cost-effective way as well, while these chil-

dren/adolescents need less complex and less expensive

treatment than children with full-syndrome ADHD.

The limitations of these findings are that only studies

published in English were included. Moreover, although

studies on both adolescents and adults found that sub-

threshold depression can be a precursor of the full-syndrome

disorder [7, 39–45], it was not possible to examine this topic

in the case of ADHD when, according to the DSM-III-R and

DSM-IV, on which studies so far are based, symptoms of

ADHD must be present before the age of seven.

In conclusion, our systematic review on subthreshold

ADHD supports the dimensional approach of ADHD. The

included studies suggested that more severe forms of

ADHD are associated with higher levels of impairment, but

the subthreshold form of this condition needs attention at

this stage. Further research on subthreshold ADHD with

uniform criteria is needed to support the inclusion of this

condition in the classification systems to assist the work of

both clinicians and researchers.

Acknowledgments This work was supported by the Hungarian

Scientific Research Fund (Hungarian abbreviation: OTKA), Grant

agreement number is K-108336.

Conflict of interest The authors declare that they have no conflict

of interest.

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Subthreshold attention deficit hyperactivity in children and adolescents: a systematic review