[Administration of creatine and creatinine with breast milk and infant milk preparations]

Creatine and creatinine intake can cause increased urinary creatinine excretion. To estimate the contribution of diet to creatinine excretion in infants, creatine and creatinine were determined in human milk, pasteurized cow's milk and formulas for preterm and term infants. Soy-based formulas did not contain creatine and creatinine. Average concentrations in human milk (creatine 77 [60-100] mumol/l, creatinine 52 [41-65] mumol/l) were markedly lower than in pasteurized cow's milk which contained 598 (476-640) mumol/l creatine and 105 (79-122) mumol/l creatinine. Creatine and creatinine concentrations differed widely in formulas for both preterm and term infants, from 155-559 and 33-174 mumol/l, respectively. The influence of ingested creatine on creatinine excretion should theoretically be negligible. On the other hand, based on known absorption data, creatinine from the diet should increase creatinine excretion in a 3-month-old infant up to an amount in the range of 5.3-28.4% of the endogenous production. Therefore creatinine ingestion should be taken into account when interpreting creatinine excretion in infants.