Cystatin C and modification of diet in renal disease (MDRD) estimated glomerular filtration rate differ during normal pregnancy

Objective. To calculate normal values for estimation of the glomerular filtration rate (eGFR) for pregnant females. eGFR is used to monitor patients with suspected kidney disease and to optimize the dosage of drugs that are eliminated by the kidneys. Plasma creatinine and cystatin C are the two most widely used GFR markers. Both markers are recommended to be automatically reported as estimated GFR. Design. Retrospective study. Setting. Tertiary university hospital. Population. We have studied creatinine (eGFR(MDRD)) (MDRD, modified diet in renal disease) and cystatin C (eGFR(cystc)) estimated GFR during 52 normal pregnancies from pregnancy week 10 to delivery and postpartum. Methods. Each woman was sampled repeatedly and the samples were grouped according to gestational age into the following periods: week 7-16; week 18-24; week 24-28; week 28-31; week 31-34; week 34-38; -2-0 weeks prior to delivery and postpartum (> 6 weeks after delivery). Main outcome measures. The 2.5 and 97.5 percentiles for these markers were calculated according to the recommendations of the International Federation of Clinical Chemistry on the statistical treatment of reference values. Results. In healthy pregnant females eGFR(cystc) was higher in the first two trimesters and lower prior to delivery in comparison with eGFR(MDRD). eGFR(cystc) and eGFR(MDRD) give different results. No significant correlations between the two estimates were found in any of the time groups. Conclusions. It is important to distinguish between the two GFR estimates and use separate reference intervals for pregnant females.