Diurnal variations of hydroxyproline and creatinine excretion in children

Urinary hydroxyproline and creatinine excretions were studied in 12 4-year-old children by collecting all individual urine specimens for a 24-hr period. Diet records were kept on the children for the same period. No consistent diurnal patterns were noted. On an individual basis the mean variation of the lowest hydroxyproline:creatinine ratio to the highest was 187%, with a range of 124 to 381%. The variations of ratios on individual samples from the ratios of the concurrent 24-hr composites ranged from 37 to 159%. When the ratios on the first specimen voided in the morning were compared with the ratios of the 24-hr composites, the range was 77 to 127% with a mean variation of 103%. There was also a close correlation between the ratios of the early morning specimen and the 24-hr ratios (r = 0.807, P < 0.01). These findings indicate that further investigation of the early morning specimen as the best sample for surveys is warranted.