ABSTRACT
BACKGROUND: There have been numerous studies to define the diurnal variation of urinary excretions of substances. It is known that this variation is influenced by many factors. This diurnal variation also affects results of quantitative analysis of random urine. The purpose of this study is to evaluate the maximum excretion time of day for representative urinary analytes and to elucidate the most appropriate time for spot urine quantitative analysis. METHODS: The concentrations of following urinary analytes were measured on healthy male and female volunteers at 06, 08, 12, 16 and 24 hours in August 1995, March 1996 and January 1997: protein, amylase, urea nitrogen, creatinine, uric acid, sodium, potassium, chloride, magnesium, calcium and inorganic phosphorus were measured by Hitachi Model 747 automatic analyzer and microalbumin by Beckman Array 360. The statistical analyses of results were performed by one-way ANOVA and multiple comparison for the significance of difference. RESULTS: The excretion of protein, amylase, urea nitrogen, creatinine, sodium, potassium, chloride, magnesium and inorganic phosphorus showed the diurnal variations. The peak excretion time of protein, amylase, urea nitrogen and creatinine was at early morning. However, that of sodium, pota-ssium, chloride, magnesium and inorganic phosphorus was at afternoon. The excretion of urea nitrogen, sodium, chloride and magnesium revealed the seasonal variations. The excretion of urea nitrogen, sodium and chloride was increased during winter. CONCLUSIONS: The morning urine specimen is considered to be the most appropriate for analysing protein and nitrogenous substances and the afternoon specimen is appropriate for electrolytes.