Sign in →

Test ID CARN Carnitine, Plasma

Reporting Name

Carnitine, P

Useful For

Evaluation of patients with a clinical suspicion of a wide range of conditions including organic acidemias, fatty acid oxidation disorders, and primary carnitine deficiency using plasma specimens

Specimen Type


Necessary Information

Patient's age is required.

Specimen Required

Collection Container/Tube:

Preferred: Green top (sodium heparin)

Acceptable: Lavender top (EDTA), green top (lithium heparin)

Submission Container/Tube: Plastic vial

Specimen Volume: 0.5 mL

Collection Instructions: Centrifuge and aliquot plasma into a plastic vial

Specimen Minimum Volume

0.2 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Plasma Frozen (preferred) 60 days
  Refrigerated  21 days
  Ambient  7 days

Reference Values


Total carnitine (TC)

Free carnitine (FC)

Acylcarnitine (AC)

AC/FC Ratio

Age Group





≤1 day





2-7 days





8-31 days





32 days-12 months





13 months-6 years





7-10 years





11-17 years





≥18 years





*Values expressed as nmol/mL

Schmidt-Sommerfeld E, Werner E, Penn D: Carnitine plasma concentrations in 353 metabolically healthy children. Eur J Pediatr. 1988;147:356-360

Used with permission of European Journal of Pediatrics.

Day(s) Performed

Monday through Friday

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
CARN Carnitine, P 97182-0


Result ID Test Result Name Result LOINC Value
32050 Total 14288-5
32051 Free (FC) 14286-9
32052 Acylcarnitine (AC) 14282-8
21032 AC/FC Ratio 30193-7
21549 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 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 renal 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.


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

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

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 May;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 Feb;23[2]:249-258)

Report Available

2 to 5 days

Reject Due To

Gross hemolysis OK
Gross lipemia OK
Gross icterus OK


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


Additional testing is required to distinguish between primary and secondary deficiencies of carnitine.


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


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

Method Name

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

Mayo Clinic Laboratories | Pediatric Catalog Additional Information: