Glomerular Filtration Rate and Error Calculation Based on the Slope-Intercept Method with Chromium-51 Ethylenediaminetetraacetic Acid via a New Clinical Software: GFRcalc

To evaluate a home-built Java-based program (GFRcalc) to simplify the calculation of glomerular filtration rate (GFR) after administration of chromium-51 ethylenediaminetetraacetic acid (51Cr-EDTA) for routine clinical use.

In the program GFRcalc, the GFR was calculated based on the biological half-life of the 51Cr-EDTA concentration using the slope-intercept method of between two and five blood samples. Additional features included the ability to export patient data and generate clinical reports as well as to calculate the error of the fit of the GFR measurement in cases with three or more blood samples collected. The GFR was calculated from one, two and three blood samples of 133 patients with body surface-corrected GFR of 21-213 ml/min/1.73 m2. The Pearson correlation coefficient and the error of the fit for the GFR measurement were calculated for the three-sample method.

The correlation coefficient for the three-sample method and the fit error correlated well for small fit errors; in case of fit errors >10%, the correlation coefficient partially differed in results compared to the other methods. The three-sample GFR values differed by approximately 17% from the single-sample GFRs. The fit errors of the three-sample GFRs correlated (r = 0.57) with their difference from the two-sample GFRs.

In this study, the fit error that GFRcalc provided for the three-sample GFR offered a simple and reliable method to check the results obtained. This could also allow physicians to assess the reliability of the results and base their decisions on the quality of the measurement.