Creatinine urine

Keywords: Urine creatinine

Specimen:

Random, 24 h or timed urine collection.

For 24 h 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 h collection depends on age, gender, muscle mass, and amount of meat in diet:

Child: 0.07-0.19 mmol/24h/kg

Adult female: 5-16 mmol/24 h 

Adult male: 9-18 mmol/24 h

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 h 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 h 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. 

5. With testing for illicit drugs.

Interpretation:

See Creatinine clearance.

Reference:

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