eGFR (mL/min/1.73m2

340.

03

0.02

300

0.0.08

220.

062

040.0.

02220.

001

080.0.

0610.

04110.

021

000.0.

0860.

0400.0.

02

Age 18 - 29

ycn

eu

qer

F

800

600

400

200

0

Std. Dev = 22.54

Mean = 103.7

N = 1534.00

eGFR (mL/min/1.73 m2

300.0

280.0

260.0

240.0

220.0

200.0

180.0

160.0

140.0

120.0

100.0

80.0

60.0

40.0

20.0

0.0

Age 30 - 39

ycn

eu

qer

F

1000

800

600

400

200

0

Std. Dev = 19.95

Mean = 95.1

N = 2303.00

eGFR (mL/min/1.73 m2

22 00.

200 .0

108

0.0.06

1104 .0

21 00.0.

00108 .0

06 .04

.0 02

.0 00.0

Age 50 - 59

ycn

eu

qer

F

1200

1000

800

600

400

200

0

Std. Dev = 18.71

Mean = 82.1

N = 3829.00

eGFR (mL/min/1.73 m2

190.

00.

081170.

0061

.015

0.004

1.0

130.

0021

.011

0.0

100.

00.0980

0.0.0760

0.5

0.040

0.3

0.0

0.021

0.00.

0

Age 40 - 49

ycn

eu

qer

F

1000

800

600

400

200

0

Std. Dev = 18.01

Mean = 87.9

N = 3542.00

eGFR (mL/min/1.73 m2

308

0.3

0.06

340.

03

0.02

0.00

32.0

800.

0622

040.

20.

022

0.00

180.

01

0.06

0.04

1102

0.1

0.00

8.0 0

60.

0400.

20.

00.0

Age 60 - 69

ycn

eu

qer

F

1600

1400

1200

1000

800

600

400

200

0

Std. Dev = 20.43

Mean = 73.8

N = 3207.00

eGFR (mL/min/1.73 m2

02 00.

18.0 0

61 00.

14.0 00.

02101 0

0.0.0806 .0

040.

02 .00.0

Age 70 +

ycn

eu

qer

F

1000

800

600

400

200

0

Std. Dev = 21.87

Mean = 61.9

N = 4917.00

CONCLUSIONS

The ranges of eGFR values obtained in these apparently healthy subjects agree with those previously published for GFR measured by inulin clearance. The suggested cut-off of 90 as normal is not applicable to this group of primary care patients; the NKF cut-off of 60 is acceptable. However, due to the wide variation in eGFR within and between age groups and the relatively high number of elderly individuals with eGFR <60, automatic reporting of the eGFR should include age-related reference intervals for people 65 years and older.

REFERENCES

1. Garg AX, Mamdani M, Juurlink DN & van Walraven C. Identifying Individuals with a Reduced GFR Using Ambulatory laboratory Database Surveillance, J Am Soc Nephrol. 2005; 16: 1433 – 1439.

2. Jones Graham RD. “Data mining” for Common Reference Intervals – Serum Sodium as an Example, AACB Annual Meeting, 2005 (Abstract).

3. Levey AS, Coresh J, Balk E, et al. NKF practice guidelines for chronic kidney disease: evaluation, classification and stratification, Ann Intern Med 2003; 139: 137 – 147.

4. Coresh J. Prevalence of chronic disease and decreased kidney function in the US population: NHANES III, Am J kidney Dis. 2003; 41: 1 – 12.

FREQUENCY DISTRIBUTION CURVES OF SINGLE RESULTS CALCULATED eGFR

eGFR (mL/min/1.73m2

Age, years

N Mean 2.5-97.5th Percentile Range

Average Estimated GFR (*)

18 – 29 1534 103.7 72.4 – 149.0 116 30 – 39 2303 95.1 63.0 – 138.4 107 40 – 49 3542 87.9 56.0 – 126.0 99 50 – 59 3829 82.1 46.0 – 120.0 93 60 – 69 3207 73.8 31.0 – 114.8 85

70 + 4917 61.9 20.0 – 105.0 75 18–70+ 19398 79.9 29.0 – 127 -

* Ontario Association of Medical Laboratories Communique November 2005, taken from Reference 4.

Percentage of Patients with eGFR within Cut-Point Age (y)

Cut-Points (mL/min/1.73 m2) <30 30 - 39 40 - 49 50 - 59 60 - 69 70+

15 – 29 (Stage 4 & 5 CKD)

0.1 0.2 0.4 0.7 1.9 6.0

30 – 59 (Stage 2 & 3 CKD)

0.4 1.0 2.7 6.9 16.5 38.2

< 60 (CKD)

0.5 1.3 3.1 7.6 18.4 44.2

> or = 90 (Normal)

75.0 57.4 42.8 29.7 18.3 9.5

60 – 89 (Reduced eGFR)

24.4 41.3 54.1 62.7 63.2 46.3 <30 30 -39 40 -49 50 -59 60 - 69 70+

Age (Y)

0

10

20

30

40

50

60

70

80

%

15 – 29

30 – 59

< 60

> or = 90

60 – 89

FIGURE 7: Percentage of Patients with eGFR (Data Set II) within Recommended Cut-Points (N=105,232)

TABLE 2: Percentage of Patients with Results within Recommended Cut-points for NKF Stages of Chronic Kidney Disease; N=105,232

TABLE 1: Mean Values And Central 95th Percentile Ranges Of eGFR(mL/min/1.73m2), Single Results

2

INTRODUCTION

Primary care (out-patients) laboratory databases have been used to identify people with low eGFR (1) and in “Data Mining” for common reference intervals (2). The National Kidney Foundation K/DOQI clinical practice guidelines recom-mend an eGFR of 60 as cut-off in determining chronic kidney disease (3). Others have stated that an eGFR of 90 or greater is normal. Therefore, the object of this study is to assess the impact of applying these cut-offs to a large cross section of patients in the primary care setting, using a private reference laboratory database.

METHODS

LABORATORY DATAGamma-Dynacare Medical Laboratories, three major sites in Central, Eastern and Southwestern Ontario; major private laboratory testing for community-based patients

DATA SET IAll serum creatinine performed on day 1, 2 or 3 post-implementation of the eGFR (representing single results, N=19,333). The eGFR was manually determined from the IDMS-traceable creatinine and MDRD equation shown below using Microsoft Excel. All values, including those >120, were included in the statistical analysis.

DATA SET IIAll serum creatinine and eGFR performed for 3 consecutive months post-implementation. The eGFR was deterimined by the Laboratory Information System (LIS) using the same equations as in Data Set I and reported as follows: eGFR <15 reported as <15, >120 reported as >120 and 15 – 120 reported as actual value (N=105,232). The data were not screened for multiple visits within the 3-month period.

STATISTICAL ANALYSIS

Statistical analyses were performed with Microsoft Excel 2000 (Microsoft Corpora-tion), Analyse-it Version 1.71 (Analyse-it Software Ltd) and SPSS for Windows, Release 10.1.01 (SPSS Inc).

RESULTS

Mean eGFR and central 95th percentile ranges for all patients, age 18 years and older, are shown in Table 1 (Data Set I). No significant differences were observed between males and females. Results compare well with published data from direct measurements (inulin clearance). Frequency distribution curves for eGFR, stratified by decades of age, are shown in figures 1 – 6. Results display normal Guassian distributions. Percentage of patients within NKF recommended cut-points for stages of chronic kidney disease are shown in Table 2 and Figure 7. The number of individuals with reduced eGFR (60 – 89) increased and then decreased with each decade of age. Fifty-one percent of all patient in the initial study (Data Set I) had eGFR results in the 60 – 89.

ASSESSMENT OF THE MDRD ESTIMATED GLOMERULAR FILTRATION RATE (eGFR, ML/MIN/1.73 M2,)

WHEN APPLIED TO A LARGE CROSS SECTION OF PATIENTS IN THE PRIMARY CARE SETTINGMoses, G.C, Vandenberghe, H., Scime, M., and Sumner, J.

Gamma-Dynacare Medical Laboratories, Brampton and London, ON.

ASSAY

1. Creatinine was determined by the kinetic colorimetric Jaffe method on the Modular System as follows:

2. The eGFR was calculated using the following equation (MDRD):

Creatinine + Picric acid Creatinine-Picric acid complex (yellow-orange) The assay is blanked and compensated to minimize effects of interfering substances.

IDMS traceable Creatinine (cCr) was derived from the regression equation:

cCr = 1.043 x Modular Creatinine + 1.695 (DigitalPT, formerly HealthMetrx)

eGFR (mL/min/1.73m2)=175 {[cCr (umol/L)/88.4]-1.154 + (Age,Yr)-0.203}x 0.742 (if female)

Solution

Alkaline

FIG 1 FIG 2 FIG 3 FIG 4 FIG 5 FIG 6