Performance of the revised '175' Modification of Diet in Renal Disease equation in patients with type 2 diabetes

Estimation of GFR (eGFR) is recommended for the assessment of kidney function in all patients with diabetes. We studied performance of the traditional '186' Modification of Diet in Renal Disease (MDRD) equation, and the 2005 revised '175' MDRD equation in patients with type 2 diabetes.

Two hundred and ninety-three mainly normoalbuminuric (267/293) patients were recruited. Patients were classified as having mild renal impairment (group 1, GFR <90 ml min(-1) 1.73 m(-2)) or normal renal function (group 2, GFR >or=90 ml min(-1) 1.73 m(-2)). eGFR was calculated by the traditional 186 MDRD equation using traditional creatinine values and the revised 175 MDRD equation using isotope dilution mass spectrometry-standardised creatinine values. Isotopic GFR was measured by the four-sample plasma clearance of (51)Cr-EDTA.

For patients in group 1, mean +/- SD isotopic (51)Cr-EDTA GFR (iGFR) was 83.8 +/- 4.3 ml min(-1) 1.73 m(-2), and eGFR was 73.2 +/- 11.9 and 75.8 +/- 13.7 ml min(-1) 1.73 m(-2) using the 186 and 175 MDRD equations, respectively. Method bias was -10.6 with the 186 MDRD and -7.9 ml min(-1) 1.73 m(-2) (p < 0.05) with the 175 MDRD equation. In group 2, iGFR was 119.4 +/- 20.2 ml min(-1) 1.73 m(-2), and eGFR was 92.3 +/- 18.6 and 97.5 +/- 21.6 ml min(-1) 1.73 m(-2) using the 186 and 175 MDRD equations, respectively. Method bias was -27.1 with the 186 MDRD equation and -21.9 ml min(-1) 1.73 m(-2) (p < 0.05) with the 175 MDRD equation.

In patients newly diagnosed with type 2 diabetes, the revised 175 MDRD equation was less biased than the traditional 186 MDRD equation. Despite a continued tendency to underestimate isotopically measured GFR, use of standardised creatinine values is a positive step towards improved estimation of GFR.