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HelpTest Code CARNU Carnitine, Random, Urine
Reporting Name
Carnitine, UUseful For
Evaluation of patients with a clinical suspicion of a wide range of conditions including organic acidemias and fatty acid oxidation disorders
Monitoring carnitine treatment
Method Name
Flow Injection Analysis-Tandem Mass Spectrometry (FIA-MS/MS)
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Specimen Type
UrineSpecimen Required
Supplies: Urine Tubes, 10 mL (T068)
Container/Tube: Plastic, 10-mL urine tube
Specimen Volume: 1.5 mL
Collection Instructions:
1. Collect a random urine specimen.
2. No preservative.
Specimen Minimum Volume
0.5 mL
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Urine | Frozen (preferred) | 365 days | |
| Refrigerated | 72 hours |
Reject Due To
All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.Reference Values
FREE CARNITINE:
77-214 nmol/mg of creatinine
TOTAL CARNITINE:
180-412 nmol/mg of creatinine
RATIO:
Acylcarnitine to free carnitine: 0.7-3.4
Day(s) Performed
Tuesday
CPT Code Information
82379
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| CARNU | Carnitine, U | 100428-2 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 27121 | Total | 17866-5 |
| 27122 | Free (FC) | 17867-3 |
| 15789 | AC/FC Ratio | 43576-8 |
| 21550 | Interpretation | 59462-2 |
Clinical Information
Carnitine and its esters are required for normal energy metabolism and serve 4 primary functions:
-Importing long-chain fatty acids into the mitochondria
-Exporting naturally occurring short-chain acyl-CoA groups from the mitochondria
-Maintaining the ratio of free CoA to esterified CoA
-Removing potentially toxic acyl-CoA groups from the cells and tissues
Evaluation of carnitine in serum, plasma, and urine is a biochemical screening test for suspected primary disorders of the carnitine cycle or for secondary disturbances in carnitine levels as a result of organic acidemias and fatty acid oxidation disorders. In the latter, acyl-CoA groups accumulate and are excreted into the urine and bile as carnitine derivatives, resulting in a secondary carnitine deficiency. More than 100 such primary and secondary disorders have been described. Collectively, their incidence is approximately 1 in 1000 live births. Primary carnitine deficiency has an incidence of approximately 1 in 21,000 live births based on Minnesota newborn screening data.
Other conditions that could cause an abnormal carnitine level include neuromuscular diseases, gastrointestinal disorders, familial cardiomyopathy, renal tubulopathies and chronic kidney failure (dialysis), and prolonged treatment with steroids, antibiotics (pivalic acid), anticonvulsants (valproic acid), and total parenteral nutrition.
Follow-up testing is required to differentiate primary and secondary carnitine deficiencies and to elucidate the exact cause.
Interpretation
When abnormal results are detected, a detailed interpretation is given, including an overview of the results and of their significance, a correlation to available clinical information, elements of differential diagnosis, recommendations for additional biochemical testing and a phone number to reach one of the laboratory directors in case the referring physician has additional questions.
Cautions
Increased values may be obtained after carnitine supplementation or meat consumption.
Method Description
Free and total carnitines are measured by tandem mass spectrometry (MS/MS) stable isotope dilution analysis. Hydrolysis enables measurement of total carnitine, and esterified carnitine (acylcarnitine) is calculated as the difference between the total and free carnitine. Quantification is enabled using deuterium-labeled carnitine (d3-carnitine) added as internal standard. A selected reaction monitoring experiment is performed by MS/MS. The first mass spectrometer detects carnitine and d3-carnitine precursors and transmits them to a collision cell within the mass spectrometer where they are fragmented. Specific fragments derived from the carnitine and internal standard are monitored in the second mass spectrometer.(Stevens RD, Hillman SL, Worthy S, Sanders D, Millington DS. Assay for free and total carnitine in human plasma using tandem mass spectrometry. Clin Chem. 2000;46(5):727-729; Miller MJ, Cusmano-Ozog K, Oglesbee D, Young S. ACMG Laboratory Quality Assurance Committee. Laboratory analysis of acylcarnitines, 2020 update: a technical standard of the American College of Medical Genetics and Genomics [ACMG]. Genet Med. 2021;23[2]:249-258)