BIOLOGICAL VARIATION IN URINE SAMPLES USED FOR ANALYTE MEASUREMENTS

To determine the influence of biological variation on the reliability of data from different types of urine specimens, we measured nine anal ytes in first-morning, randomly collected, and 24-h samples of urine f rom 53 healthy individuals (14 men and 39 women). The urines were coll ected once a week for 10 weeks. The data obtained were used as a basis for specimen collection and to gain insight into the influence of uri ne quantities in the diagnosis, screening, and monitoring of patients. We found that 24-h urine expressed in output rather than concentratio n units is the most reliable specimen for diagnosis and monitoring for most of the analytes studied. On the basis of the ratio between estim ated within- and between-subject variation, the tests with greatest me dical usefulness for diagnosis and screening of specific pathologies a re those measuring protein and sodium. Moreover, the results indicate that urine creatinine may be a poor test for diagnosis, monitoring, an d screening.