Variation in excretion of certain amino acids with age.

By relating amino acid excretion to creatinine excretion in a specimen of urine from fasting patients, the normal variation of cystine, glutamine, glycine, and alanine excretion in relation to creatinine excretion and the age of the individual has been defined. No amino acid excretion differences between the two sexeswere detectable. In general, the excretion levels for these four amino acids were found to be highest in infancy and decreased markedly with age. However, this decrease is not a uniform or gradual one. The greatest decrease occurs between the 3-5-year and 6-8-year groups, and the excretion levels again increase slightly between the 9-il-year and 12-14-year groups.