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Epic Code LAB1230023 Carnitine, Random, Urine

Additional Codes

Mayo Code: CARNU

Epic Code: LAB 1230023

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Useful 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

Specimen Type

Urine


Specimen 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.

Day(s) Performed

Tuesday

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

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.

Cautions

Increased values may be obtained after carnitine supplementation or meat consumption.

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.

Reporting Name

Carnitine, U

Method Name

Flow Injection Analysis-Tandem Mass Spectrometry (FIA-MS/MS)

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)

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

Report Available

3 to 9 days

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.

Clinical Reference

1. Magoulas PL, El-Hattab AW. Systemic primary carnitine deficiency: an overview of clinical manifestations, diagnosis, and management. Orphanet J Rare Dis. 2012; 18;7:68

2. Longo N, Amat di San Filippo C, Pasquali M. Disorders of carnitine transport and the carnitine cycle. Am J Med Genet C Semin Med Genet. 2006 15;142C(2):77-85

3. Zammit VA, Ramsay RR, Bonomini M, Arduini A. Carnitine, mitochondrial function and therapy. Adv Drug Deliv Rev. 2009;61(14):1353-1362

4. El-Hattab AW: Systemic primary carnitine deficiency. In: Adam MP, Ardinger HH, Pagon RA, et al, eds. GeneReviews [Internet]. University of Washington, Seattle; 2012. Updated November 3, 2016. Accessed November 27, 2023. Available at www.ncbi.nlm.nih.gov/books/NBK84551/

5. Almannai M, Alfadhel M, El-Hattab AW. Carnitine inborn errors of metabolism. Molecules. 2019;24(18):3251

6. Longo N., Frigeni M., Pasquali M. Carnitine transport and fatty acid oxidation. Biochim. Biophys. Acta. 2016;1863(10):2422-2435

Highlights

Carnitine levels are disturbed in primary disorders of the carnitine cycle, or secondary disturbances of carnitine metabolism due to other biochemical disorders.

 

While plasma or serum carnitine is reduced in primary carnitine deficiency, urine carnitine may be normal or elevated.

 

Dietary intake (meat, carnitine supplementation) may cause increased carnitine values.

 

Abnormal results are accompanied by detailed interpretation including recommendations for follow-up testing.