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Test ID: CARNU Carnitine, Random, Urine

Reporting Name

Carnitine, U

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


Specimen Required

Supplies: Urine Tubes, 10 mL (T068)

Container/Tube: Plastic, 10-mL urine tube

Specimen Volume: 1.5 mL

Collection Instructions: Collect a random urine specimen.

Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Urine Frozen (preferred) 365 days
  Refrigerated  72 hours

Reference Values


77-214 nmol/mg of creatinine



180-412 nmol/mg of creatinine



Acylcarnitine to free carnitine: 0.7-3.4

Day(s) Performed


Test Classification

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

CPT Code Information


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.


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.

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 Sep 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 May 15;142C(2):77-85

3. Zammit VA, Ramsay RR, Bonomini M, Arduini A: Carnitine, mitochondrial function and therapy. Adv Drug Deliv Rev. 2009 Nov 30;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 16, 2021. Available at

5. Almannai M, Alfadhel M, El-Hattab AW: Carnitine inborn errors of metabolism. Molecules. 2019 Sep 6;24(18):3251

Report Available

2 to 8 days

Method Name

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

Mayo Clinic Laboratories | Genetics and Pharmacogenomics Catalog Additional Information: