Variability in creatinine excretion in adult diabetic, overweight men and women: Consequences on creatinine-based classification of renal disease

BackgroundIt is crucial to estimate renal function in diabetic patients. However, formulas are inadequate in this population whereas creatinine clearance (Ccr) on a 24-h urine collection may be valuable only if we can improve its reproducibility.ObjectiveTo evaluate in diabetic patients whether standardised procedures of 24-h urine collection improve the day-to-day variability in creatinine urinary excretion and the subsequent precision of the measured Ccr.MethodsThe Ccr from two consecutive 24-h urine collections was measured in 201 consecutive diabetic inpatients. Procedures of 24-h urine collection were standardised, and implementation was supervised at a diabetes clinic.ResultsPearson's correlation coefficients of the two 24-h creatinine urinary excretion were significant (r2 = 0.64 in women and r2 = 0.65 in men, p < 0.0001) but the daily variability in creatinine urinary excretion was high (14.9% in women and 17.4% in men). As a consequence, the agreement between the two consecutive measurements of Ccr was poor. First, Bland–Altman plots showed large 95% limits of agreement (−34.3 to 34.6 mL/min/1.73 m2 in women and −39.0 to 52.0 mL/min/1.73 m2 in men). Secondly, there was a poor agreement for classifying patients according to the National Kidney Foundation classification >90, 60–89.9, 30–59.9, and <30 mL/min/1.73 m2 (Kappa coefficients = 0.61, 0.42, 0.65, and 0.74, respectively).ConclusionsDespite standardised procedures of 24-h urine collection, day-to-day variability in creatinine urinary excretion in adult diabetic men and women remains important, and may lead to misclassification of renal disease.