Variability of creatinine excretion of normal, phenylketonuric and galactosemic children, and children treated with anticonvulsant drugs.

Creatinine per minute excretion rates in individual voidings varied as much as 300-500 percent of the 24-hour value for several children. Creatinine excretion rates were significantly more variable for children treated with anticonvulsant drugs than for normal children. Riboflavin-creatinine ratios determined on individual voidings were variable but adequate although total riboflavin was low. No time of day was found when creatinine excretion was representative of the 24-hour value. The creatinine height index when calculated from timed individual voidings during a 24-hour period varied for some children from 0.5 to more than 1.5 times published norms.