Single- versus multiple-sample method to measure glomerular filtration rate

Abstract

Background. There are many different ways to measure glomerular filtration rate (GFR) using various exogenous filtration markers, each having their own strengths and limitations. However, not only the marker, but also the methodology may vary in many ways, including the use of urinary or plasma clearance, and, in the case of plasma clearance, the number of time points used to calculate the area under the concentration time curve, ranging from only one (Jacobsson method) to eight (or more) blood samples. Methods. We collected the results obtained from 5106 plasma clearances (iohexol or 51Cr-ethylenediaminetetraacetic acid (EDTA)) using three to four time points, allowing GFR calculation using the slope intercept method and the Bro chner- Mortensen correction. For each time point, the Jacobsson formula was applied to obtain the single-sample GFR. We used Bland Altman plots to determine the accuracy of the Jacobsson method at each time point. Results. The single-sample method showed within 10% concordances with the multiple-sample method of 66.4%, 83.6%, 91.4% and 96.0% at the time points 120, 180, 240 and300min, respectively. Concordance was poorer at lower GFR levels, and this trend is in parallel with increasing age. Results were similar in males and females. Some discordance was found in the obese subjects. Conclusion. Single-sample GFR is highly concordant with a multiple-sample strategy, except in the low GFR range (<30mL/min).