How reliable is estimation of glomerular filtration rate at diagnosis of type 2 diabetes?
OBJECTIVE
The Cockcroft-Gault (CG) and Modification of Diet in Renal Disease (MDRD) equations previously have been recommended to estimate glomerular filtration rate (GFR). We compared both estimates with true GFR, measured by the isotopic (51)Cr-EDTA method, in newly diagnosed, treatment-naïve subjects with type 2 diabetes.


METHODS
A total of 292 mainly normoalbuminuric (241 of 292) subjects were recruited. Subjects were classified as having mild renal impairment (group 1, GFR <90 ml/min per 1.73 m(2)) or normal renal function (group 2, GFR >/=90 ml/min per 1.73 m(2)). Estimated GFR (eGFR) was calculated by the CG and MDRD equations. Blood samples drawn at 44, 120, 180, and 240 min after administration of 1 MBq of (51)Cr-EDTA were used to measure isotopic GFR (iGFR).


RESULTS
For subjects in group 1, mean (+/-SD) iGFR was 83.8 +/- 4.3 ml/min per 1.73 m(2). eGFR was 78.0 +/- 16.5 or 73.7 +/- 12.0 ml/min per 1.73 m(2) using CG and MDRD equations, respectively. Ninety-five percent CIs for method bias were -11.1 to -0.6 using CG and -14.4 to -7.0 using MDRD. Ninety-five percent limits of agreement (mean bias +/- 2 SD) were -37.2 to 25.6 and -33.1 to 11.7, respectively. In group 2, iGFR was 119.4 +/- 20.3 ml/min per 1.73 m(2). eGFR was 104.4 +/- 26.3 or 92.3 +/- 18.7 ml/min per 1.73 m(2) using CG and MDRD equations, respectively. Ninety-five percent CIs for method bias were -17.4 to -12.5 using CG and -29.1 to -25.1 using MDRD. Ninety-five percent limits of agreement were -54.4 to 24.4 and -59.5 to 5.3, respectively.


CONCLUSIONS
In newly diagnosed type 2 diabetic patients, particularly those with a GFR >/=90 ml/min per 1.73 m(2), both CG and MDRD equations significantly underestimate iGFR. This highlights a limitation in the use of eGFR in the majority of diabetic subjects outside the setting of chronic kidney disease.
Chudleigh
Richard A
RA
Diabetes Research Unit, Llandough Hospital, Penlan Road Penarth, Cardiff CF64 2XX. rachudleigh@hotmail.com
Dunseath
Gareth
G
Evans
William
W
Harvey
John N
JN
Evans
Philip
P
Ollerton
Richard
R
Owens
David R
DR
D000368:Aged; D000419:Albuminuria / Q000453:epidemiology; D001794:Blood Pressure; D015992:Body Mass Index; D003924:Diabetes Mellitus, Type 2 / Q000503:physiopathology* / Q000652:urine; D003928:Diabetic Nephropathies / Q000453:epidemiology; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006442:Glycated Hemoglobin / Q000032:analysis; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results
D006442:Glycated Hemoglobin