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Test ID FAO Fatty Acid Oxidation Probe Assay, Fibroblast Culture

Reporting Name

Fatty Acid Ox Probe Assay, Fibro

Useful For

In vitro confirmation of biochemical diagnoses of the following fatty acid oxidation disorders:

-Short-chain acyl-CoA dehydrogenase deficiency

-Medium-chain acyl-CoA dehydrogenase deficiency

-Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency

-Trifunctional protein deficiency

-Very long-chain acyl-CoA dehydrogenase deficiency

-Carnitine palmitoyl transferase deficiency type II

-Carnitine-acylcarnitine translocase deficiency


Confirmation of the following organic acid disorders:

-2-Methylbutyryl-CoA dehydrogenase deficiency

-Isobutyryl-CoA dehydrogenase deficiency


This test is not useful for prenatal testing.


This assay is not informative if the deficient enzyme is physiologically not expressed in skin fibroblasts.

Additional Tests

Test ID Reporting Name Available Separately Always Performed
CULFB Fibroblast Culture for Genetic Test Yes Yes

Testing Algorithm

When this test is ordered, fibroblast culture testing will always be performed at an additional charge. If viable cells are not obtained, the client will be notified.

Specimen Type


Ordering Guidance

This test is recommended only after appropriate analyte testing, including acylcarnitines, organic acids, acylglycines, and/or fatty acids has been performed.


For more information see:

-ACRN / Acylcarnitines, Quantitative, Plasma

-OAU / Organic Acids Screen, Random, Urine

-AGU20 / Acylglycines, Quantitative, Random, Urine

-FAPCP / Fatty Acid Profile, Comprehensive [C8-C26], Serum

Necessary Information

Provide clinical information

Specimen Required

Submit only 1 of the following specimens:


Specimen Type: Cultured fibroblasts

Container/Tube: T-75 or T-25 flask

Specimen Volume: 1 Full T-75 flask or 2 full T-25 flasks

Specimen Stability Information: Ambient (preferred)/Refrigerated 24 hours


Specimen Type: Skin biopsy

Supplies: Fibroblast Biopsy Transport Media (T115)

Container/Tube: Sterile container with any standard cell culture media (eg, minimal essential media, RPMI 1640). The solution should be supplemented with 1% penicillin and streptomycin. Tubes can be supplied upon request (Eagle's minimum essential medium with 1% penicillin and streptomycin).

Specimen Volume: 4-mm punch

Specimen Stability Information: Refrigerated (preferred)/Ambient

Specimen Stability Information

Specimen Type Temperature Time Special Container
Tissue Varies

Reference Values

An interpretive report will be provided.

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
FAO Fatty Acid Ox Probe Assay, Fibro 74533-1


Result ID Test Result Name Result LOINC Value
23487 Interpretation 59462-2
23489 Reviewed By 18771-6

Clinical Information

Mitochondrial fatty acid beta-oxidation plays an important role in energy production during periods of fasting. When the body's supply of glucose is depleted, fatty acids are mobilized from adipose tissue, taken up by the liver and muscles, and oxidized to acetyl-CoA. In the liver, acetyl-CoA is the building block for the synthesis of ketone bodies, which enter the blood stream and provide an alternative substrate for production of energy in other tissues when the supply of glucose is insufficient to maintain a normal level of energy. Disorders of fatty acid oxidation (FAO) are characterized by hypoglycemia, hepatic dysfunction, encephalopathy, skeletal myopathy, and cardiomyopathy. Most FAO disorders have a similar presentation, and their biochemical diagnosis can, at times, be difficult. Commonly used metabolite screens such as urine organic acids, plasma acylcarnitines, and fatty acids are influenced by dietary factors and the clinical status of the patient. This can lead to incomplete diagnostic information or even false-negative results. The purpose of the in vitro probe assay is to offer screening for several defects of FAO and organic acid metabolism under controlled laboratory conditions using fibroblast cultures.


Abnormal results will include a description of the abnormal profile in comparison to normal and abnormal controls. In addition, the concentration of those acylcarnitine species that abnormally accumulated in the cell medium are provided and compared to the continuously updated reference range based on analysis of normal controls.


Interpretations of abnormal acylcarnitine profiles also include information about the results' significance, a correlation to available clinical information, possible differential diagnoses, recommendations for additional biochemical testing and confirmatory studies if indicated, name and phone number of contacts who may provide these studies, and a phone number to reach one of the laboratory directors in case the referring provider has additional questions.


Sometimes, an abnormal acylcarnitine profile cannot differentiate between 2 disorders. In such instances, independent biochemical (eg, specific enzyme assay when available) or molecular genetic analyses are required. Recommendations for such testing will be included in the report.

Clinical Reference

1. Ensenauer R, Vockley J, Willard JM, et al: A common mutation is associated with a mild, potentially asymptomatic phenotype in patients with isovaleric acidemia diagnosed by newborn screening. Am J Hum Genet. 2004;75(6):1136-1142. doi: 10.1086/426318

2. Rinaldo P, Matern D, Bennet MJ: Fatty acid oxidation disorders. Ann Rev Physiol. 2002;64:477-502

3. Shen JJ, Matern D, Millington DS, et al: Acylcarnitines in fibroblasts of patients with long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency and other fatty acid oxidation disorders. J Inherit Metab Dis. 2000;23:27-44. doi: 10.1023/a:1005694712583

4. Matern D, Huey JC, Gregersen N, et al: In vitro diagnosis of short-chain acyl-CoA dehydrogenase (SCAD) deficiency. J Inherit Metab Dis. 2001;24(Suppl.1):66

5. Merritt JL, Norris M, Kanungo S: Fatty acid oxidation disorders. Ann. Transl. Med. 2018 Dec;6(24):473. doi: 10.21037/atm.2018.10.57

Method Description

Skin fibroblasts are incubated with cell medium enriched with palmitic acid (C16:0 fatty acid), L-carnitine, and isotopically labeled L-valine ([13]C-Val) and L-isoleucine ([13]C-Ile). Cell lines deficient of one of the enzymes involved in fatty acid oxidation and branched chain amino acid metabolism fail to metabolize acyl-CoA species, which accumulate in the cell medium as acylcarnitines. The medium is separated from the cells following the incubation. The cell pellet is used for protein determination and the medium will be spotted and dried on filter paper. An acylcarnitine analysis is performed by tandem mass spectrometry using a 1/4" filter paper punch, following the addition of isotopically labeled acylcarnitines as internal standards, extraction and derivatization to methyl esters. The assay is performed in triplicate.(Matern D: Acylcarnitines, incl. in vitro loading tests. In: Blau N, Duran M, Gibson KM, eds. Laboratory Guide to the Methods in Biochemical Genetics. Springer-Verlag; 2008; Cowan T, Pasquali M: Laboratory investigations of inborn errors of metabolism. In: Sarafoglou K, Hoffman GF, Roth KS, eds. Pediatric Endocrinology and Inborn Errors of Metabolism. 2nd ed. McGraw-Hill; 2017:1139-1158)

Report Available

15 to 71 days depending on rapidity of growth

Reject Due To

Specimen in formalin or fixative preservative Reject

Method Name

Fibroblasts Incubated with Enriched Medium followed by Tandem Mass Spectrometry (MS/MS)


1. New York Clients-Informed consent is required. Document on the request form or electronic order that a copy is on file. The following documents are available:

-Informed Consent for Genetic Testing (T576)

-Informed Consent for Genetic Testing-Spanish (T826)

2. Biochemical Genetics Patient Information (T602)

3. If not ordering electronically, complete, print, and send a Biochemical Genetics Test Request (T798) with the specimen.