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Carnitine and Acylcarnitine
MessageOrder Miscellaneous Test Quest Test Code 15948.
Test Code
15948
Alias/See Also
15948
CPT Codes
82017, 82379
Preferred Specimen
2 mL frozen plasma collected in a sodium heparin (green-top)
Patient Preparation
Patient should be in a well-fed state
Minimum Volume
1 mL
Other Acceptable Specimens
Serum
Instructions
Collect blood sample in sodium heparin (green-top) tube. Separate plasma by centrifugation as soon as possible. Avoid hemolysis. Remove plasma and place in plastic tube. Freeze immediately after separation.
Date of birth required.
Date of birth required.
Transport Temperature
Frozen
Specimen Stability
Room temperature: Unacceptable
Refrigerated: Unacceptable
Frozen: 30 days
Refrigerated: Unacceptable
Frozen: 30 days
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Gross hemolysis • Received room temperature • Received refrigerated
Methodology
Chromatography/Mass Spectrometry
FDA Status
This test was developed and its analytical performance characteristics have been determined by Quest Diagnostics. It has not been cleared or approved by the U.S. Food and Drug Administration. This assay has been validated pursuant to the CLIA regulations and is used for clinical purposes.
Setup Schedule
Set up and Report available: See individual assays
Reference Range
See Laboratory Report
Clinical Significance
A plasma acylcarnitine profile is one of the most powerful and accurate methods to diagnose inborn errors of fatty acid metabolism and organic acidemias. In newborn screening, newborns have sufficient free carnitine provided through the placenta from the mother to make acylcarnitine profiling alone sufficient to rule out these inborn errors.
Unfortunately, after the newborn period, at the time of presentation and diagnosis, many patients with these disorders have become chronically depleted of free carnitine due to the inability to recycle esterified carnitine. In this situation, the acylcarnitine profile may be normal with all values in the lower end of the normal range despite the patient being affected with a disorder of fatty acid oxidation or an organic acidemia. Recently, we had just such a case with a patient known to have methylmalonic acidemia because of organic acid analysis who initially had a normal acylcarnitine profile.
In such cases, a carnitine analysis would have shown extremely low free carnitine and very elevated carnitine esters and would have prompted carnitine supplementation of the patient followed by further periodic evaluations.
As clinicians come to rely increasingly on acylcarnitine profiling to diagnose inborn errors of metabolism, it will be important to assay both carnitine (free and esterified) simultaneously with acylcarnitines for the initial evaluation of children for inborn errors of metabolism. This approach would prevent false negative results and false reassurance that could occur if acylcarnitines alone were ordered.
Unfortunately, after the newborn period, at the time of presentation and diagnosis, many patients with these disorders have become chronically depleted of free carnitine due to the inability to recycle esterified carnitine. In this situation, the acylcarnitine profile may be normal with all values in the lower end of the normal range despite the patient being affected with a disorder of fatty acid oxidation or an organic acidemia. Recently, we had just such a case with a patient known to have methylmalonic acidemia because of organic acid analysis who initially had a normal acylcarnitine profile.
In such cases, a carnitine analysis would have shown extremely low free carnitine and very elevated carnitine esters and would have prompted carnitine supplementation of the patient followed by further periodic evaluations.
As clinicians come to rely increasingly on acylcarnitine profiling to diagnose inborn errors of metabolism, it will be important to assay both carnitine (free and esterified) simultaneously with acylcarnitines for the initial evaluation of children for inborn errors of metabolism. This approach would prevent false negative results and false reassurance that could occur if acylcarnitines alone were ordered.
Performing Laboratory
| Quest Diagnostics Nichols Institute-San Juan Capistrano, CA |
| 33608 Ortega Highway |
| San Juan Capistrano, CA 92675-2042 |
Last Updated: March 17, 2023
