[Correlation between 24-hour urinary protein excretion and protein/creatinine ratio in the first voided morning urine...

To collect 24-hour urine of infants and young children is so difficult that 24-hour urinary protein excretion (24 H-UP) has been estimated from single voided urine samples. We investigated the correlation between 24 H-UP and the protein/creatinine ratio of the first voided morning urine samples (MUP/Cr) and evaluated the problems associated with this method. Six hundred and thirty-nine specimens, pairs of morning spot urine and 24-hour collected urine, were collected from 158 patients, aged 3 to 28, who were being followed at Kyoto City Hospital. The study population was divided into different subgroups by age, disease category and inpatient or outpatient status and linear regression analysis was performed for every subgroup. Although MUP/Cr correlated well with 24 H-UP, it was necessary to revise the estimation of 24 H-UP from MUP/Cr, which is lower in infants and young children because of age-related differences in creatinine excretion. If the patient's age is younger, the creatinine excretion rate is lower. The difference in 24 H-UP estimated from MUP/Cr was significant between inpatients and outpatients, with the estimated value being higher in outpatients than inpatients. The estimated value was also different according to disease category. We speculated that the difference in estimated 24 H-UP was affected by different rate of creatinine excretion related to age and other factors.