Abstract
This brief review examines the history of the use of creatinine as a measure of renal function. While there are more accurate markers of glomerular filtration, creatinine was chosen for convenience. Since the relationship of creatinine to glomerular filtration depends upon a tenuous balance of counterbalancing factors, practitioners should be alert to situations that alter that balance. While the averaging of variations over time helps to avoid some of the problems with diurnal variations in the past, the present-day reliance upon equations based upon a solitary serum value is likely to amplify those problems in clinical situations when the effect of disease, medications, diet and time of day upon that balance are not considered.