Creatinine excretion: variability and relationships to diet and body size.

Abstract

Abstract In general, rates of addition of creatine to and loss of creatinine from the precursor pool depend upon the dietary intake and synthesis of creatine and the conversions of phosphoryl creatine and creatine to creatinine. Meat in a usual diet can appreciably expand the pool because of the slow turnovers of the precursors. Thus, 24 hour urinary creatinine contains a component from that day's turnover of stored creatine ingested previously. During this study, ingestion of creatine and creatinine free, but adequate protein diets, adjusted pool size toward supply and demand and lowered creatinine excretion as much as 30 per cent. For any population, correlation coefficients between estimates of body size or metabolically effective tissue and urinary creatinine depend in part on the expansion of the precursor pool. By serial daily creatinine analyses over long experimental periods on a metabolic ward, timing artifact in 24 hour collections was minimized; this is an important source of error if single 24 hour or random samples are used.