Preferred Specimen(s) 2 mL urine
Instructions Record 24-hour urine volume on test request form and urine vial.
Transport Container 24-hour urine container
Transport Temperature Ambient 7 days, Refrigerated 62 days
Reject Criteria Received at room temperature
Methodology Spectrophotometry
Clinical Significance Creatinine is the end product of creatine metabolism. Creatine is present primarily in muscle and the amount of creatinine produced is related to total skeletal muscle mass. Daily creatinine production is fairly constant except when there is massive injury to muscle. The kidneys excrete creatinine very efficiently and blood levels and daily urinary excretion of creatinine fluctuates very little in healthy normal people. Since blood and daily urine excretion of creatinine shows minimal fluctuation, creatinine excretion is useful in determining whether 24-hour urine specimens for other analytes (e.g., protein) have been completely and accurately collected.