Variability of Urinary Creatinine in Healthy Individuals.

Gerd Sallsten,Lars Barregard

doi:10.3390/ijerph18063166

Abstract

Many urinary biomarkers are adjusted for dilution using creatinine or specific gravity. The aim was to evaluate the variability of creatinine excretion, in 24 h and spot samples, and to describe an openly available variability biobank. Urine and blood samples were collected from 60 healthy non-smoking adults, 29 men and 31 women. All urine was collected at six time points during two 24 h periods. Blood samples were also collected twice and stored frozen. Analyses of creatinine in urine was performed in fresh urine using an enzymatic method. For creatinine in urine, the intra-class correlation (ICC) was calculated for 24 h urine and spot samples. Diurnal variability was examined, as well as association with urinary flow rate. The creatinine excretion rate was lowest in overnight samples and relatively constant in the other five samples. The creatinine excretion rate in each individual was positively correlated with urinary flow rate. The creatinine concentration was highest in the overnight sample and at 09:30. For 24 h samples the ICC was 0.64, for overnight samples it was 0.5, and for all spot samples, it was much lower. The ICC for urinary creatinine depends on the time of day of sampling. Frozen samples from this variability biobank are open for researchers examining normal variability of their favorite biomarker(s).

Highlights

Biomarkers of exposure or biomarkers of effects are often used in occupational health surveillance and in epidemiological research
Variability of creatinine excretion is of special interest since it is commonly used to “normalize” concentrations of biomonitoring results in urine spot samples which otherwise are greatly affected by varying diuresis [4]
This paper describes the within- and between-individual variability of creatinine excretion in 60 healthy individuals, both the diurnal variability and variability in 24 h samples

Summary

Introduction

Biomarkers of exposure or biomarkers of effects are often used in occupational health surveillance and in epidemiological research. For most biomarkers there is, limited information about normal day-to-day variability within individuals in the general population. For urinary biomarkers there may be diurnal variability making it important to fix the time of day the sampling is performed, but again there is very limited information in the literature about diurnal variability. This is true when biomarkers in urine are adjusted for dilution using creatinine or specific gravity. Variability of creatinine excretion in timed samples has rarely been studied and the relation between creatinine excretion and urinary flow rate is unclear [2,3]. Variability of creatinine excretion is of special interest since it is commonly used to “normalize” concentrations of biomonitoring results in urine spot samples which otherwise are greatly affected by varying diuresis [4]

Methods

Results

Discussion

Conclusion