Comparison of estimated creatinine clearance among five formulae (Cockroft-Gault, Jelliffe, Sanaka, simplified 4-variable MDRD and DAF) and the 24hours-urine-collection creatinine clearance

Abstract

Background: GFR estimation is of major importance in everyday clinical practice. Usually it is done using one of the many eGFR equations available. In this study we compared in our population four widespread eGFR equations and our own empirical eGFR, with creatinine clearance calculated through a timed urine collection.

Patients and methods: We collected laboratory data of 907 patients from our clinic and outpatient department through a ten-year period and statistically compared the eGFR results between them and with the timed urine collection creatinine clearances.

Results: All eGFR equations gave acceptable approximations to the timed urine collection creatinine clearances. However, in different subpopulations some equations did better than others, without any clear advantage of any equation overall. Surprisingly, our empirical equation named DAF also gave acceptable approximations regardless of age, weight and sex of the patient.

Conclusions: In our population our empirical eGFR method (DAF) gave satisfactory results regarding the monitoring of renal function, compared with four other eGFR methods. We suggest that it could provide a very fast and easy to use means of eGFR calculation.

Keywords: clearance; creatinine; eGFR; renal failure.

Figure 1. We can see the overall graphical comparison of the clearance rates between the 24hour urine collection (black dots) and the Diamandopoulos' formula (DAF, red dots). Here the rates of the DAF are clearly inside the rates of the 24hour urine collection

Figures 2 to 5. The reader can see the close correlation between DAF and the other eGFR methods. DAF lays in almost the same trajectory with Cockroft-Gault and Sanaka, while giving slightly higher GFRs than SMDRD and Jelliffe

Figures 6 to 8. We see that in the overall comparisons, Bland-Altman analysis shows similar satisfactory results for the three equations

Figures 9 to 11. In the stage III data, while all three equations gave acceptable correlation with 24h urine collection clearances, DAF had far the smallest bias, a result that comes in accordance with the paired t-test