Test ID: CTU
Creatinine, Urine
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
Urinary creatinine, in conjunction with serum creatinine, is used to calculate the creatinine clearance, a measure of renal function.
Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test
Method Name A short description of the method used to perform the test
Enzymatic Colorimetric Assay
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Aliases Lists additional common names for a test, as an aid in searching
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
Container/Tube: Plastic, 6-mL tube (Supply T465)
Specimen Volume: 5 mL
Collection Instructions:
1. Collect urine for 24 hours.
2. No preservative.
Additional Information:
1. 24 Hour volume is required.
2. See Urine Preservatives in Special Instructions for multiple collections.
Urine Preservative Collection Options
| Ambient | Preferred |
| Refrigerated | Yes |
| Frozen | Yes |
| 6N HCl | Yes |
| 50% Acetic Acid | Yes |
| Na2CO3 | Yes |
| Toluene | Yes |
| 6N HNO3 | Yes |
| Boric Acid | Yes |
| Thymol | Yes |
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | NA |
| Lipemia | NA |
| Icterus | NA |
| Other | NA |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Urine | Refrigerated (preferred) | 30 days |
| Ambient | 30 days | |
| Frozen | 30 days |
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Creatinine is formed from the metabolism of creatine and phosphocreatine, both of which are principally found in muscle. Thus the amount of creatinine produced is in large part dependent upon the individual's muscle mass and tends not to fluctuate much from day-to-day.
Creatinine is not protein-bound and is freely filtered by glomeruli. All of the filtered creatinine is excreted in the urine. Renal tubular secretion of creatinine also contributes to a small proportion of excreted creatinine. Although most excreted creatinine is derived from an individual's muscle, dietary protein intake, particularly of cooked meat, can contribute to urinary creatinine levels.
The renal clearance of creatinine provides an estimate of glomerular filtration rate.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
15-25 mg/kg of body weight/24 hours
Reported in unit of mg/specimen
Interpretation Provides information to assist in interpretation of the test results
24-Hour urinary creatinine determinations are principally used for the calculation of creatinine clearance.
Decreased creatinine clearance indicates decreased glomerular filtration rate. This can be due to conditions such as progressive renal disease, or result from adverse effect on renal hemodynamics that are often reversible including certain drugs or from decreases in effective renal perfusion (eg, volume depletion or heart failure).
Increased creatinine clearance is often referred to as "hyperfiltration" and is most commonly seen during pregnancy or in patients with diabetes mellitus, before diabetic nephropathy has occurred. It also may occur with large dietary protein intake.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
The reliability of 24-hour urinary creatinine determinations are, as for all timed urine collections, very dependent on accurately collected 24-hour specimens.
Intraindividual variability in creatinine excretion may be due to differences in muscle mass or amount of ingested meat.
Acute changes in GFR, before a steady state has developed, will alter the amount of urinary creatinine excreted.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Newman DJ, Price CP: Renal function and nitrogen metabolites. In Tietz Textbook of Clinical Chemistry. 3rd edition. Edited by CA Burtis, ER Ashwood. Philadelphia, WB Saunders, 1999, pp 1204-1270
2. Kasiske BL, Keane WF: Laboratory assessment of renal disease: clearance, urinalysis, and renal biopsy. In The Kidney. 6th edition. Edited by BM Brenner. Philadelphia, WB Saunders, 2000, pp 1129-1170
Method Description Describes how the test is performed and provides a method-specific reference
The enzymatic method is based on the determination of sarcosine from creatinine with the aid of creatininase, creatinase, and sarcosine oxidase. The liberated hydrogen peroxide is measured via a modified Trinder reaction using a colorimetric indicator. Optimization of the buffer system and the colorimetric indicator enables the creatinine concentration to be quantified both precisely and specifically. (Package insert: Roche Diagnostics, Indianapolis IN, 2004)
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Monday through Sunday; Continuously
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
82570
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| CRE_A | Creatinine, U | 2162-6 |
| TM10 | Collection Duration | 13362-9 |
| VL8 | Urine Volume | 3167-4 |
| NCTU_ | Creatinine Conc | 2161-8 |
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