URINARY HYDROXYPROLINE - CREATININE RATIO IN NORMAL TERM, PRE-TERM, AND GROWTH-RETARTED INFANTS

In normal term and growth-retarded infants during the first week of life, 20-30% of the total urinary hydroxyproline is excreted as free hydroxy-proline. Pre-term infants excrete 35-40% of the total hydroxyproline in the free form. Total hydroxyproline excretion is therefore not a valid measure of skeletal growth in the newborn infant. The hydroxyproline/creatinine ratio correlated well in 24-hour urine collections and in random urine samples obtained during the same 24-hour period, thus making 24-hour urine collections unnecessary for this purpose. The peptide hydroxyproline/creatinine ratio during the first week of life agrees well with the pattern of growth expected during this period of life. Ratios in pre-term infants are significantly higher and in growth-retarded infants significantly lower than in normal term infants on the first day of life. There is a rapid increase in the ratio during the first week, less in pre-term infants. Thus, the peptide hydroxyproline/creatinine ratio appears to be a valid index of growth in the perinatal period.