Creatinine, 24-Hour Urine
Code:7009|CPT:82570|LOINC:2161-8, 2162-6
| Includes | Creatinine, Urine Creatinine, Ur 24hr |
|---|
Analysis details
Methodology
- Kinetic Jaffe method
Expected Turnaround Time
1 day
Special Instructions
- Record the total 24-hour urine volume on the test requisition.
- Avoid alcohol for 24 hours before starting and throughout the collection period.
- For 12 hours before collection, avoid spicy or salty foods and items that can discolor urine (eg, beetroot, carrots).
- With clinician approval only, hold diuretics for 48 hours before and during the collection.
- Avoid strenuous physical activity and significant emotional stress during the 24-hour collection.
How to use
Creatinine, 24-Hour Urine (urine creatinine; 24-hour urine creatinine) is used to evaluate kidney function alongside serum creatinine and the recorded collection volume to derive creatinine clearance as an estimate of glomerular filtration rate. The test supports diagnostic assessment and ongoing monitoring of acute and chronic kidney disease. The measured 24-hour urinary creatinine additionally serves as a crude indicator of completeness for timed urine collections performed for other laboratory analytes.
Limitations
Creatinine (1-methylglycocyamidine) is generated from creatine and phosphocreatine predominantly in skeletal muscle. Under usual physiologic conditions it is removed from plasma by glomerular filtration with minimal tubular reabsorption. For a given individual, daily urinary creatinine output is fairly constant but varies with muscle mass, age, and sex; excretion is generally higher in men than in women and children. Concurrent serum and 24-hour urine creatinine measurements permit calculation of creatinine clearance, which is used as an estimate of glomerular filtration rate. At very low urine flow rates, tubular reabsorption of creatinine can occur, reducing urinary creatinine excretion. This pattern is observed in settings such as severe congestive heart failure, uncontrolled diabetes mellitus, and acute renal failure.
| Unit | mg/24h | ||||
|---|---|---|---|---|---|
| Reference interval |
| ||||
| Indications | Baseline appraisal of renal function during general health evaluation., Workup of suspected kidney disease when clinical signs are present, including edema (periorbital or lower-extremity), abnormal urine characteristics, flank pain, or voiding abnormalities., Assessment in conditions commonly involving the kidneys, such as hypertension, diabetes mellitus, systemic lupus erythematosus, and vasculitis., Monitoring response to therapy in acute or chronic kidney disease., Verification of completeness of 24-hour urine collections used for other analytes. |
Possible Causes of Abnormal Results
Increased levels
- ascorbic acid
- cefazolin
- cefoxitin
- cephalothin
- corticosteroids
- fluoxymesterone
- meat ingestion
- methotrexate
- methyldopa
- nandrolone
- nitrofurantoin
- nitrofurazone
- oxymetholone
- prednisolone
- pregnancy
- strenuous exercise
Decreased levels
- acute renal failure
- captopril
- cimetidine
- ketoprofen
- low urine flow
- probenecid
- quinapril
- severe congestive heart failure
- thiazide diuretics
- trimethoprim
- uncontrolled diabetes mellitus
Specimen Requirements
| Specimen | Urine |
|---|---|
| Container | 24-Hour Urine Collection Container |
| Volume | 10 mL (min 0.5 mL) |
| Storage Instructions | Room temperature, Refrigerated, Frozen |
References
Fischbach F.T., Dunning M.B. A Manual of Laboratory and Diagnostic Tests, 8th Ed. Lippincott Williams & Wilkins, 2008: 1344 p.