Observations on the variability of creatinine excretion.

This paper reports the intra-individual variability of creatinine excretion under conditions of variable food intake and stress. Urine collections over 24 h were made by six subjects for 24 d in the course of an expedition to the Colombian Andes. The average coefficient of variation (CV) of day-to-day creatinine excretion was 11.4 per cent and of N excretion 28 per cent. When the outputs were averaged by 3-d period the mean CV of creatinine excretion was reduced to 5.7 per cent. It is concluded that in metabolic studies the 3-d creatinine excretion is a useful index even when food intakes and other conditions are not controlled.