Miller and Lifshitz report using the creatinine excretion in a well-collected 24 hour urine as a benchmark for comparing the adequacy of future urine collections. As long as a patient's muscle mass is stable the urine excretion of creatinine should be relatively constant. A sudden drop in urinary creatinine excretion may indicate an incomplete collection.
Requirements:
(1) A reference 24 hour urine collection for comparison (for example, one collected in a hospital by nursing personnel)
(2) Using the same or an analytically similar method for measuring the urine creatinine (so not an analytical artifact from using 2 different methods)
(3) Stable muscle mass (no significant increase in exercise schedule, starvation, myopathy or protein malnutrition) and stable renal function.
excretion of creatinine in the urine in mg per 24 hours =
= (24 hour urine in mL) / 100 * (urine creatinine in mg/dL)
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