Creatinine - urine

Last updated: Thursday, 15, April, 2004

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Item Process
Specimen

Random, 24 hour or timed urine collection.

For 24 hour or timed collections, the starting and finishing time must be stated, to the nearest minute, on the specimen container.

Method

Spectrophotometry.

Reference Interval

Random urine collection is dependent on rate of urine flow.

24 hour collection depends on age, gender, muscle mass, and amount of meat in diet:
Child: 0.07-0.19 mmol/24 hours/kg
Adult female: 5-16 mmol/24 hours 
Adult male: 9-18 mmol/24 hours.

Application

Urine creatinine is of no diagnostic value in its own right. It is measured in the following circumstances:

  1. As a guide to the completeness of a 24 hour urine collection.
  2. With another urine analyte to calculate the analyte/creatinine ratio. This corrects for variability in urine dilution (random urine specimen) or compensates for an incomplete 24 hour urine collection.
  3. With plasma creatinine and another analyte present in both plasma and serum, to calculate a fractional excretion rate of that analyte (eg, sodium).
  4. With plasma creatinine, to estimate plasma creatinine clearance.
Interpretation

See Creatinine clearance.

Reference

Pasternack A and Kuhlback B. Scand J Clin Lab Invest 1971; 27: 1-7.