modification of diet in renal disease [MDRD] equation underestimates glomerular filtration rate [GFR] in egyptian kidney donors

ABSTRACT

Inulin clearance and radioisotopic studies are the most accurate methods of GFR measurement, but are expensive. The K/DOQ1 guidelines recommended estimating GFR by using the Modification of Diet in Renal Disease [MDRD] or Cockcroft-Gault [CG] equations. So far, the MDRD equation has not been validated for GFR estimation in healthy donors. We examined the accuracy of the MDRD equation and creatinine clearance based on 24 hour urine collection in the prediction of GFR in a group of healthy donors in comparison with radionuclide measured GFR. We retrospectively examined the medical records of 100 of kidney donors who underwent [99M]Tc-diethylenetri amine-pentaacetic acid [DTPA] renal clearance and creatinine clearance at the transplant outpatient clinic, Cairo University Hospital between June 2002 and July 2006. GFR was predicted with the abbreviated MDRD formula without the variable for black. We examined the significant differences, potential correlations and agreements between the predicted and measured GFR. The mean eGFR [MDRD] was 8.16% lower than [99M]Tc-DTPA GFR [116.11 +/- 25.44 ml/ min/ 1.73 m[2] Vs. 126.32 +/- 24.21 ml/min/1.73 m[2], the difference range -84 to +61 ml/ min/ 1.73 m[2], p=0.002]. CrCl was 13.14% higher than [99M]Tc-DTPA GFR [142.90 +/- 27.51 ml/min 1.73 m[2], the difference range +65 to -60 ml/min/1.73 m[2], p<0.001]. A significant positive correlation was observed when CrCl and [99M]Tc-DTPA measured GFR were compared [r=0.451, r[2]=0.203, p=0.000]. No significant correlation was noted between eGFR MDRD and [99M] Tc-DTPA measured GFR [r=0.126, r[2]=0.016, p=0.211]. Linear regression analysis showed that at eGFR[MDRD] <99.37 ml/min/1.73 m[2], eGFR [MDRD] underestimated the DTPA GFR values. Bland Altman analysis showed poor agreement between GFR[MDRD] and CrCL on the one hand and measured GFR on the other hand [+54.2/-74.6 and +70/-36.8 respectively]. Our results indicate that neither MDRD equation nor CrCl are accurate in predicting GFR in healthy donors. Using MDRD in healthy individual might carry the risk of underestimating GFR in individuals with normal kidney function