Detection of impaired renal function

Abstract

Summary Aim: Renal function is usually determined by means of creatinine-clearance, and of serum Cystatin C, the latter with increasing frequency. The present study analyses, whether the diagnostic accuracy of 99mTc-MAG3 clearance is comparable to that of these modern serologic methods. Patienten, Methods: 71 consecutive adult Caucasian patients (42 female, 29 male; age 50 ± 16 yrs., range 20 – 83) who were referred to a nuclear medicine department for determination of bilateral renal function with 99mTc-MAG3 were included. Following sufficient hydration, 10 ml of blood were taken for determination of Cystatin C and creatinine in serum prior to i.v. injection of the radiotracer. According to the recommendations of the National Kidney Foundation, glomerular filtration rate (GFR) was calculated from serum creatinine using either Cockcroft & Gault and Modification of Diet in Renal Disease (MDRD) study equation. These estimates of GFR served as reference. Cystatin C is a low molecular protein produced by all nuclear cells and is eliminated to 85 % by glomerular filtration. Analysis of 99mTc-MAG3 clearance was performed by means of Bubeck’s formula. Results: Linear regression analysis produced Pearson’s correlation coefficients of r = 0.68 and r = -0.69 for the comparison of either Cystatin C and 99mTc-MAG3 clearance with the Cockcroft & Gault equation. The comparison of Cystatin C and 99mTc-MAG3 clearance with MDRD study equation resulted in correlation coefficients of r = 0.755 and r = -0.77. None of these differences were significant. The exclusion of renal impairment or the detection of an at least moderate renal impairment revealed again no significant differences between Cystatin C and 99mTc-MAG3 clearance. Conclusions: Cystatin C and 99mTc-MAG3 clearance are equally suited to exclude renal impairment or to detect a relevant renal impairment. Differences between both procedures are more likely a result of the applied reference method.