Creatinine
Code:8022
| Includes | Creatinine, urine concentration Creatinine, 24-hour excretion |
|---|
Analysis details
Methodology
- Kinetic Jaffe method
Expected Turnaround Time
1 day
Special Instructions
- Avoid alcohol during the 24 hours before the collection begins.
- For 12 hours before starting, avoid spicy or salty foods and items that can discolor urine (eg, beets, carrots).
- Unless instructed by the clinician, do not take diuretics for 48 hours before the collection.
- Limit strenuous physical activity and emotional stress throughout the 24-hour collection period.
How to use
The 24-hour urine creatinine test is used to assess renal excretory and filtration function and to monitor patients with established kidney disease. It also verifies the adequacy of timed (24-hour) urine collections. Urine creatinine serves as a normalization factor for other urinary measurements that are reported per gram or per millimole of creatinine.
Limitations
Creatinine is generated from muscle creatine and phosphocreatine at a relatively constant rate and is eliminated by the kidneys with minimal tubular reabsorption. Urine concentrations are higher by several orders of magnitude compared with serum. For a given individual, daily urinary creatinine excretion is fairly stable and correlates with muscle mass, with expected differences by sex and age. When serum creatinine and a 24-hour urine creatinine are obtained together, creatinine clearance can be calculated to estimate glomerular filtration rate. Because timed urinary creatinine output varies little, it is used to assess the completeness of 24-hour urine collections and to normalize other urine analytes, such as protein or albumin.
| Unit | mmol/24h | ||||
|---|---|---|---|---|---|
| Reference interval |
Depends on your age | ||||
| Indications | Routine preventive or wellness assessment, Clinical features suggesting kidney dysfunction, including edema, abnormal urinalysis, flank pain, or lower urinary tract symptoms, Chronic disorders with potential renal involvement (hypertension, diabetes mellitus, systemic lupus erythematosus, vasculitis), Therapeutic monitoring in patients with kidney disease, Checking completeness of 24-hour urine collections used for other analytes (eg, hormones, proteins) |
Possible Causes of Abnormal Results
Increased levels
- ascorbic acid
- cefazolin
- cefoxitin
- cephalothin
- corticosteroids
- fluoxymesterone
- high meat intake
- methyldopa
- methotrexate
- nandrolone
- nitrofurantoin
- nitrofurazone
- oxymetholone
- physical exertion
- pregnancy
Decreased levels
- anabolic steroids
- captopril
- ketoprofen
- quinapril
- thiazide diuretics
Specimen Requirements
| Specimen | Serum |
|---|---|
| Container | Gold/Tiger Top (SST, Gel Separator) |
| Storage Instructions | Refrigerated |
References
Fischbach F.T., Dunning M.B. A Manual of Laboratory and Diagnostic Tests, 8th Ed. Lippincott Williams & Wilkins, 2008: 1344 p.