Evaluation of variability of proteinuria indices.

We compared several indices of proteinuria, namely protein concentration, hourly protein excretion rate (Up/h) and protein/creatinine ratio (Up/Ucr) in single voided urine samples as well as 24 h-urinary protein excretion (24 h-Up), in 44 children, aged 4-16 years, with varying degrees of urinary protein excretion. We found an excellent correlation between Up/h and Up/Ucr in early morning samples. These two indices in early morning samples had excellent correlation with 24 h-Up, comparable to those in any other urine sample of the day. Among daytime samples, Up/h varied widely, in contrast to Up/Ucr, which had significantly less variability. We analysed six early morning and six bedtime samples from 39 of these subjects, and found smaller coefficients of variation for individual patient's indices in morning samples. Up/h was more variable than Up/Ucr, especially in bedtime samples. Urinary protein concentration had a poorer correlation with 24 h-Up and was more variable than any other index. We conclude that the Up/Ucr in early morning samples, which has the advantages both of simplicity and low day-to-day variability in a given patient, is a superior index of proteinuria.