Comparison of plasma clearance with early-compartment correction equations and urinary clearance in high glomerular filtration rate ranges

Abstract Introduction Glomerular filtration rate (GFR) is measured from the late plasma disappearance curve of an exogenous tracer, after correction for the early decay – corresponding to the distribution of the tracer – using various equations. These equations display the highest discrepancies in the GFR range above 90 ml/min/1.73m2, and their respective performances against a reference, urinary GFR measurement are unclear. Methods In patients with mGFR >90 ml/min/1.73m2 from six different cohorts, we compared GFR obtained from the plasma clearance of iohexol or 51Cr-EDTA, after correction using Chantler (C), Brochner-Mortensen (BM), Fleming (F), Jodal-Brochner-Mortensen (JBM), and Ng (N) equations, with urinary clearance of the same tracers or inulin. Results In 438 participants (median age 41 [ 39;42] years, 43% women), median urinary clearance was 100.8 [94.7;112.6] mL/min/1.73m2. Plasma clearances using the correction equations were 105.7 [96.8;119.2], 102.4 [95.2;112.9], 100.7 [93.6;111.1], 102.6 [95.2;113.4], and 106.0 [98.2;117.6] mL/min/1.73m2, for C, BM, F, JBM, and N, respectively. Concordance correlation coefficients between plasma and urinary clearances were poor for all equations. Compared to urinary clearances, BM, F, and JBM displayed the best accuracy within 10% (73, 72 and 71% respectively, versus 63 and 66% for C and N), while BM and JBM had the lowest median biases. Accuracy of all equations was especially low in the hyperfiltration range (urinary clearance >130 ml/min/1.73m2). Conclusion The BM and JBM equations displayed the best overall performances to correct for the early disappearance curve. Results of these equations should be interpreted with caution, especially in the highest GFR range.