Average creatinine–urea clearance: revival of an old analytical technique?

BACKGROUND: Creatinine-based equations such as the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) are recommended for estimating glomerular filtration rate (eGFR) in clinical practice, but have reduced performance in advanced stages of chronic kidney disease. However, only rarely studies have evaluated the performance of eGFR by measuring the average of the urinary clearances of creatinine and urea (mCl(UN-cr)) compared with the eGFR equations. METHODS: This cross-sectional study evaluated the usefulness of mCl(UN-cr) in a population of 855 participants who performed a GFR measurement by urinary inulin clearance. The performance of mCl(UN-cr) was compared with those of CKD-EPI 2009 and CKD-EPI 2021, considering three criteria: bias, precision and accuracy. RESULTS: In the whole sample, the mCl(UN-cr) performed similarly to CKD-EPI equations (2009 and 2021) [precision: 11.5 (95% CI 10.5; 12.5) vs 19.0 (95% CI 17.2; 20.1) and 19.1 (95% CI 17.4; 20.4), and accuracy P(30): 97.0 (95% CI 95.8; 98.0) vs 82.0 (95% CI 79.2; 84.4) and 77.2 (95% CI 74.5; 80.0)]. The CKD-EPI equations (2009 and 2021) had the best performance when mGFR was >60 mL/min/1.73 m(2). In contrast, the mCl(UN-cr) performed better than others with lowest mGFR values, more noticeable when mGFR was <60 mL/min/1.73 m(2). CONCLUSIONS: The study described the best performance of mCl(UN-cr) at GFR levels below 60 mL/min/1.73 m(2) and a satisfactory result in the overall cohort. The findings point to a role of this tool, especially for estimating GFR in chronic kidney disease patients in developing countries, when reference measurement of GFR is not available.