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8/10/2019 SKRENING untuk
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Screening test
OLEH
dr.Siswanto,MSc
Ilmu kesehatan masyarakat
F.K. UNIBRAW.
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1. DEFINITION OF SCREENING
The presumptive identification of unrecognized
disease or defect by the application of test, examination,
or other procedures which can be applied rapidly to sortout apparently well persons who probably have a
disease from those who probably do not.
A screening test is not intended to be diagnostic. Personwith positive or suspicious findings must be referred to
their physicians for diagnosis.
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2. AIMS OF SCREENING TEST
To detect early stages of disease so that treatment can begiven ( diagnose dini)
3. DISEASE APPROPRIATE FOR SCREENING
a. Disease that often are fatal or have seriousconsequences with prolonged morbidity.
b. The disease must have a treatment that, when applied
to the screen-detected stage of the disease, is moreaffective than treatment applied after symptoms haveled to diagnosis.There is no point in screening for adisease that can be treat successfully after symptomsappear.
c. The detectable preclinical phase (DPCP) of diseaseshould have a high prevalence among the personsscreened.
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Two important concepts for screening :
1. Individuals with a disease can be identified by a
screening test before the time of routinediagnosis ( eg, when symptoms occur)
2. Treatment at the time of detection by screening,
as opposed to the time of routine diagnosis,
result in an improved chance of survival
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SUITABLE SCREENING TESTHigh validity ( Accuracy)
High reliability ( Precision)
Low cost
None or low side effects
Convenient and painless as possible
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Validity of the test : The extent to whichthe test is capable of correctly diagnosing
the present or absence of the diseaseconcerned.
Sensitivity : The ability of the test to detectpeople who actually have the disease(a/a+c)
Spesificity : The ability of the test to detectpeople who actually do not have the
disease. (d/b+d)
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BAKU EMAS
Baku emas yang dipakai sebagai
pembanding tidak boleh mengandung unsur
atau komponen yang diuji
Baku emas tidak boleh mempunyai
sensitivitas dan spesifitas lebih rendah dari
test screning yang diuji
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PREDICTIVE VALUE OF THE TEST
Positive predictive value. ( a/a+b)The probality that a person who tested positive on
the test actually had the disease.
Negative predictive value. ( d/c+d).
The probality that a person who tested negative truly
did not had the disease.
9
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Positive Predictive Value ( Nilai Duga
Positif)
Probabilitas seseorang sakit bila uji skrening positif
A / A + B
Negative Predictive Value ( Nilai Duga
Negatif)
Probabilitas seseorang tidak sakit bila uji skreningnegatif
D / C + D
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DISEASE
(GOLD STANDARD)SCREENING
-
TOTAL
SCREENING
TEST +
A
(TRUE POSITIVE)
B
(FALSE POSITIVE)
A + B
SCREENING
TEST -
C
(FALSE
NEGATIVE)
D
(TRUE NEGATIVE)
C + D
TOTAL A + C B + D A+B+C+D
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HASIL PATOLOGI ANATOMI
SCREENING
-
TOTAL
USG
KELENJAR
TIROID +
18 16 34
USG
KELENJARTIROID -
2 64 66
TOTAL 20 80 100
SENSITIVITAS : 18/20 + 100 % = 90 %
SPESIFISITAS : 64/80 + 100 % = 80 %
N D + : 18/34 = 53 %
N D - : 64/66 = 97 %
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Uses of specific tests
( A specific test should be chosen)
When false positive results can harm the patient
physically, emotionally or financially.
Exp: cancer
15
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16
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17
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RELIABILITY
The extent to which repeated measurement of a
relatively stable phenomenon fall closely to each
other.
Reproducibility and precision are otherwords for this property.
19
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VARIATION
Source Definition
Measurement
Instrument The means of making the
measurement
Observer The person making the
measurement
Biologic
Within individuals Changes in people with time and
situation
Among individuals Biologic differences from person to
person20
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Variation
Measurement Variation : All observation aresubject to variation resulting from measurement
because of the performance of the instrument and
observers.
Reduce
Standard protocols Machines ( Automatic)
21
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Variation
Fetal heart rate : Auscultation vs Electronicmonitoring
22
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RELIABILITY ( KEANDALAN,
REPRODUSIBILITAS)Suatu pengukuran disebut andal apabila alat test mem-
berikan nilai yang sama atau hampir sama apabila
pemeriksaan dilakukan ber ulang ulang.
Keandalan dipengaruhi oleh:
Variasi metoda
Variasi intra dan antar observer
Variasi subyek
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PENILAIAN KEANDALAN PENGUKURAN
1. Varibel numerik.
Dengan menghitung Koefisien Variasi ( KV) yaitu :hasil simpang baku (standard deviation) dibagi denganrerata ( mean).
Contoh : pengukuran kadar natrium serum dilakukandengan dua cara yaitu cara A dan cara B masing masingdilakukan 20 kali pemeriksaan dengan hasil sbb:
Cara A : 136, 132,133, 137, 134, 135, dst
Cara B : 135, 139, 132, 132, 130,136 dst
Cara A : Rerata 134,7 Simpang baku 1,76 KV= 0,013
Cara B : Rerata 134,7 Simpang baku 2,71 KV= 0,020
Pengukuran A lebih andal dari B
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2. Variabel nominalDengan menentukan nilai Kappa (k)
Hasil pemeriksaan thorax photo dari penderita yang dicurigai TBColeh dua dokter A dan B
NO DOKTER A DOKTER B NO DOKTER A DOKTER B
1 Normal Normal 16 Normal Abnormal
2 Abnormal Abnormal 17 Normal Normal
3 Normal Abnormal 18 Abnormal Normal
4 Normal Normal 19 Normal Abnormal
5 Normal Normal 20 Abnormal Abnormal
6 Abnormal Abnormal 21 Normal Abnormal
7 Abnormal Abnormal 22 Normal Normal
8 Abnormal Normal 23 Normal Abnormal
9 Abnormal Abnormal 24 Normal Normal
10 Normal Abnormal 25 Abnormal Normal
11 Normal Normal 26 Abnormal Normal
12 Normal Normal 27 Abnormal Abnormal
13 Abnormal Abnormal 28 Normal Abnormal
14 Abnormal Abnormal 29 Abnormal Abnormal15 Abnormal Normal 30 Normal Normal
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NORMAL TIDAK
NORMAL
A
9
B
7 16
TIDAK
C
4
D
10 14
13 17 30
Kesesuaian nyata = (9+10)/30 = 63,3 %
Kesesuaian karena peluang = (16x13)/30 + (14x17)/30 =14,9 %
Kesesuaian bukan karena peluang = (63,3-14,9) % =48,4 %
Potensi kesesuaian bukan karena
peluang (100-14,9) % = 85,1 %
ARTI KAPPA TEST
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ARTI KAPPA TEST
Under 20 % negligible
20% to 40% minimal
>40% to 60% fair
>60% to 80% good
>80% excellent28
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STRATEGI MENINGKATKAN KEANDALAN
1. Standarisasi cara pengukuran
Contoh : membuat Protap yaitu aturan yangterperinci untuk melaksakan pengukuran
Mengatasi kesalahan pada : pengamat dan subyek
2. Pelatihan pengamatMengatasi kesalahan pada :pengamat
Dengan peningkatan kemampuan dari pengamatuntuk melaksanakan pengukuran maka kemungkinan
kesalahan makin kecil.
Kesamaan kemampuan dari antar pengamat jugasangat diperlukan untuk meningkatkan keandalan.
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3. Penyempurnaan dan automatisasi instrumenMengatasi kesalahan dari alat ukur, pengamat dan subyek
Contoh : pemeriksaan kadar Hb dengan menggunakan
spektrofotometer jauh lebih baik dari pemeriksaan sahli
4. Mengulang pengukuran
Mengatasi kesalahan pada : pengamat, subyek dan alatukur.