Standard reference for daily urinary creatinine excretion among individuals with obesity: a monocentric, retrospective, observational study

Abstract

Background: Urinary collection over 24 h is a cornerstone in the care of patients with nephrolithiasis, obesity, hypertension, and chronic kidney disease (CKD). The completeness of 24-h urinary collection is assessed by urinary creatinine excretion, which reflects the muscle mass. Hence, it is of paramount importance to define expected values of daily urinary creatinine excretion to correctly interpret urinary collection. These references are available for the general population. We hypothesized that these reference values might not be applicable to individuals with obesity whose body composition is different from general population.

Objectives: Our objective was to define daily urinary creatinine excretion among population with obesity.

Methods: We conducted a monocentric, retrospective, observational study, including adult patients (≥18 y) admitted for measurement of glomerular filtration rate (GFR). Measurement of GFR requires timed urinary collections to calculate the urinary clearance of the tracer. We took advantage of timed urinary collection to calculate in-hospital urinary creatinine flow rate and to extrapolate it to 24 h (exUCreat₂₄ for extrapolated 24-h creatinine excretion). We compared exUCreat₂₄ between patients with obesity and healthy weight matched on height, age, sex, ethnic origin, 24-h urinary urea, and nonindexed GFR.

Results: We included 1091 patients [median age 56 y, interquartile range (44, 67); 62.7% males] with nondialysis CKD stages 1-5. Among them, 227 were obese. The exUCreat₂₄ was higher among individuals with obesity than in healthy weight patients [13.9 (11.1, 17.3) compared with 11.0 (8.8, 13.9) mmol/24h; P < 0.01]. The 10th and 90th percentiles of exUCreat₂₄ corrected for weight of individuals with obesity were significantly different from the 10th and 90th percentiles previously reported in the literature for the general population (P < 0.01).

Conclusion: Daily urinary creatinine excretion is significantly higher among individuals with obesity than in healthy weight population. We propose new standard reference for urinary creatinine excretion in individuals with obesity.

Keywords: daily urinary creatinine excretion; glomerular filtration rate; muscle mass; obesity; overweight.