Reference values for analytes of 24-h urine collections known to be complete

One hundred and twenty two 24-h urine collections were obtained from a representative sample of men and women in the general population aged 25-44 years. The collections were verified for their completeness by urine recovery of oral doses of para-amino benzoic acid. Means (with 0.95 reference intervals) for both sexes for 24-h urinary output were determined for nitrogen, urea, creatinine, urate, ammonia, sodium, potassium, volume, and pH. Within person variation in nitrogen, urea, creatinine, ammonia, sodium and potassium was estimated for a consecutive 28-day series of 24-h urine collections for eight individuals. Within person variation was greatest for sodium and least for creatinine. These differences when compared with the between person variation in the analytes studied have implications for the precision with which a result from a single specimen can be used to place an individual within a distribution of values for epidemiological purposes. In clinical biochemistry, the population results reported here should be appropriate as a reference base for comparison with individual patient results.