3-Methylhistidine/creatinine ratio in urine from low-birth-weight infants. Statistical analysis.

3-Methylhistidine and creatinine concentrations were determined in 45 24-hour urine samples collected in 380 single voidings from 23 preterm infants (gestational age: 30-36 weeks, median: 33 weeks; birth weight: 1,613 +/- 219 g; age: 9-83 days postpartum) and from 7 infants small for gestational age (birth weight: 2,061 +/- 203 g; age: 2-30 days postpartum). Statistical analysis shows that diurnal variations of the ratio 3-methylhistidine/creatinine are negligible. The variability of this ratio is chiefly caused by differences in excretion on different collection dates and is probably due to differences in the metabolic state. Hence the determination of 3-methylhistidine/creatinine ratio in single voidings is sufficient even in low-birth-weight infants. In our collective the mean 3-methylhistidine/creatinine ratio for healthy, well-growing low-birth-weight infants (n = 21) was 19.6 +/- 2.3 mumol/mmol. Infants with stagnating or decreasing weight (n = 5) showed 3-methylhistidine/creatinine ratios clearly above that of the normal group.