Possibilities of evaluation of changes of glomerular filtration rate estimated on the basis of predicting formulas
Abstract
Introduction: Estimation of changes of glomerular filtration rate based on accurate measurement (GFR) and that based on predicting formulas (eGFR) could differ significantly. In this study we have tried to analyse the relationship between (eGFR)t2//(eGFR)t1 and (GFR)t2/(GFR) t1 (where t1 and t2 denote the time at the beginning and the end of the follow-up interval).
Methods: Renal clearance of inulin (Cin) was repeatedly examined in 32 patients suffering from chronic renal impairment (SCr = 231 +- 70 μmol/l). Estimated GFR (eGFR) was calculated on the basis of Modification of Diet in Renal Disease (MDRD) and Cockcroft-Gault (CG) equations.
Results: A significant relationship between (MDRD)t2/(MDRD)t1 and (Cin)t 2/(Cin)t1 (r = 0.544, p = 0.0028, R2 = 0.295) as well as between (CG)t2/(CG)t1 and (C in)t2/(CG)t1 (r = 0.556, p = 0.0026, R 2 = 0.309) was found. Average difference between (MDRD)t 2/(MDRD)t1 - (Cin)t2/(C in)t1 was 0.017 +- 0.17 and that of (CG)t 2/(CG)t1 - (Cin)t2/(C in)t1 was 0.024 +- 0,18.
Within +- 0.20 of the difference (eGFR)t2/(eGFR)t1 - (Cin)t 2/(Cin)t1 59 % values were found and within +- 0.30 of this difference 75 % values were recorded. Highly significant relationship was found between (MDRD)t2/(MDRD)t1 and (CG)t2/(CG)t1 (r = 0.991; p = 0.0001; R2 = 0.983).
Conclusion: Considering these preliminary findings, predicting formulas are not sensitive sufficiently to by able to detect GFR changes lower than 30 % of initial value