Test Catalog

Test ID: CARNU    
Carnitine, Random, Urine

Useful For Suggests clinical disorders or settings where the test may be helpful

Evaluation of patients with a clinical suspicion of a wide range of conditions including organic acidemias and fatty acid oxidation disorders


Monitoring carnitine treatment

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

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 screens patients 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 1,000 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.

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.


77-214 nmol/mg of creatinine



180-412 nmol/mg of creatinine



Acyl to free: 0.7-3.4

Interpretation Provides information to assist in interpretation of the test results

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 Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

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

Clinical Reference Recommendations for in-depth reading of a clinical nature

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

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;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 GeneReviews Edited by MP Adam, HH Ardinger, RA Pagon, et al. University of Washington, Seattle; 1993-2019. 2012 Mar 15 (Updated 2016 Nov 3) Accessed 3/22/2019. Available at www.ncbi.nlm.nih.gov/books/NBK84551/