Free cortisol and creatinine in urine of healthy children

Cortisol and creatinine were measured in two consecutive overnight urine collections from 103 healthy school children, ages seven to 18.5 years. Mean cortisol and creatinine concentrations were respectively 194 nmol/L and 12.7 mmol/L. The data were statistically analyzed to simultaneously assess any effects of sex, age, weight, day of collection, and urine volume. Mean urine volume for boys exceeded that for girls, increased with body weight, and was greater on the second day of collection than on the first. Cortisol concentration was independent of sex, age, and weight, but decreased with urine volume. Boys excreted more cortisol than did girls, and the amount increased with urine volume. Creatinine concentration increased with weight, decreased with urine volume. Total creatinine increased with weight, was greater for boys than girls, and increased with urine volume. The cortisol/creatinine ratio was valueless as an index of adrenocortical status.