Abstract
BackgroundUrinary creatinine excretion is used as a marker of completeness of timed urine collections, which are a keystone of several metabolic evaluations in clinical investigations and epidemiological surveys.The current reference values for 24-hour urinary creatinine excretion rely on observations performed in the 1960s and 1970s in relatively small and mostly selected groups, and may thus poorly fit to the present-day general European population.The aim of this study was to establish and validate anthropometry-based age- and sex-specific reference values of the 24-hour urinary creatinine excretion on adult populations with preserved renal function.MethodsWe used data from two independent Swiss cross-sectional population-based studies with standardised 24-hour urinary collection and measured anthropometric variables. Only data from adults of European descent, with estimated glomerular filtration rate (eGFR) ≥60 ml/min/1.73 m2 and reported completeness of the urinary collection were retained. A linear regression model was developed to predict centiles of the 24-hour urinary creatinine excretion in 1,137 participants from the Swiss Survey on Salt and validated in 994 participants from the Swiss Kidney Project on Genes in Hypertension.ResultsThe mean urinary creatinine excretion was 193 ± 41 μmol/kg/24 hours in men and 151 ± 38 μmol/kg/24 hours in women in the Swiss Survey on Salt. The values were inversely correlated with age and body mass index (BMI).Based on current reference values (177 to 221 μmol/kg/24 hours in men and 133 to 177 μmol/kg/24 hours in women), 56% of the urinary collections in the whole population and 67% in people >60 years old would have been considered as inaccurate.A linear regression model with sex, BMI and age as predictor variables was found to provide the best prediction of the observed values and showed a good fit when applied to the validation population.ConclusionsWe propose a validated prediction equation for 24-hour urinary creatinine excretion in the general European population, based on readily available variables such as age, sex and BMI, and a few derived normograms to ease its clinical application. This should help healthcare providers to interpret the completeness of a 24-hour urine collection in daily clinical practice and in epidemiological population studies.
Highlights
Urinary creatinine excretion is used as a marker of completeness of timed urine collections, which are a keystone of several metabolic evaluations in clinical investigations and epidemiological surveys
We propose a validated prediction equation for 24-hour urinary creatinine excretion in the general European population, based on readily available variables such as age, sex and body mass index (BMI), and a few derived normograms to ease its clinical application
In the Swiss Kidney Project on Genes in Hypertension (SKIPOGH) study, 994 people were considered as the validation population for the present analysis, after excluding 60 people for incomplete urine collection and 3 for over-collection
Summary
Urinary creatinine excretion is used as a marker of completeness of timed urine collections, which are a keystone of several metabolic evaluations in clinical investigations and epidemiological surveys. Measurement of urinary creatinine excretion in the clinical and research fields has multiple purposes: 1) to measure creatinine clearance as a surrogate of the glomerular filtration rate [2]; 2) to estimate average 24-hour excretion rates of several solutes including electrolytes and proteins from spot urine samples, using the respective ratios to urinary spot creatinine concentration [4,5,6,7]; 3) to assess lean body mass [1,8]; and 4) to check the completeness of 24-hour urine collections [9,10] The latter can be estimated from knowledge of the normal rate of creatinine excretion, which is equal to creatinine production in the steady state. In the case of a single patient’s measure and in large scale epidemiologic studies, the identification of over- and under- collection of 24-hour urine samples remains a crucial but difficult task [10,13]
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