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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 (SCAD) deficiency

-Medium-chain acyl-CoA dehydrogenase (MCAD) deficiency

-Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency

-Trifunctional protein deficiency

-Very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency

-Carnitine palmitoyl transferase deficiency type II (CPT-II)

-Carnitine-acylcarnitine translocase (CACT) deficiency


Confirmation of the following organic acid disorders:

-2-Methylbutyryl-CoA dehydrogenase (SBCAD) deficiency

-Isobutyryl-CoA dehydrogenase (IBD) 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.

Clinical Information

Mitochondrial fatty acid beta-oxidation plays an important role in energy production, particularly in skeletal and heart muscle, and in hepatic ketone body formation. 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 often leads to incomplete diagnostic information or even false-negative results. Enzyme assays are limited to one enzyme per assay, and molecular assays for common genetic variants are limited by the frequent occurrence of compound heterozygous patients with uncommon, private alterations, which must be distinguished from unaffected carriers. Furthermore, neither specific enzyme assays nor molecular genetic testing are available for all of the known defects. 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.

Testing Algorithm

When this test is ordered, a fibroblast culture and cryopreservation for biochemical studies will always be performed at an additional charge. However, for multiple assays on a patient utilizing fibroblast culture, only 1 culture is required regardless of the number of assays ordered. If viable cells are not obtained within 30 days, client will be notified.


See Newborn Screening Follow-up for Isolated C5 Acylcarnitines Elevations (also applies to any plasma or serum C5 acylcarnitine elevations) in Special Instructions.

Analytic Time

15 to 71 days depending on rapidity of growth

Day(s) and Time(s) Performed


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 Name

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

CRYOB: Fibroblast Subculture followed by Cryopreservation and Storage

Specimen Type


Advisory Information

This test is recommended only after appropriate analyte testing, including acylcarnitines, organic acids, acylglycines, and/or fatty acids (ACRN / Acylcarnitines, Quantitative, Plasma; OAU / Organic Acids Screen, Urine; ACYLG / Acylglycines, Quantitative, Urine; FAPCP / Fatty Acid Profile, Comprehensive [C8-C26], Serum), has been performed.

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.

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 U.S. Food and Drug Administration.

CPT Code Information

82017-Acylcarnitines; quantitative, each specimen

88233-Fibroblast culture

88240-Cryopreservation for biochemical studies

LOINC Code Information

Test ID Test Order Name Order LOINC Value
FAO Fatty Acid Ox Probe Assay, Fibro 35574-3


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

Additional Tests

Test ID Reporting Name Available Separately Always Performed
FIBR Fibroblast Culture Yes Yes
CRYOB Cryopreserve for Biochem Studies No Yes


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 in Special Instructions:

-Informed Consent for Genetic Testing (T576)

-Informed Consent for Genetic Testing-Spanish (T826)

2. Biochemical Genetics Patient Information (T602) in Special Instructions.

3. If not ordering electronically, complete, print, and send an Inborn Errors of Metabolism Test Request (T798) with the specimen.

Mayo Clinic Laboratories | Neurology Catalog Additional Information:

mml-Pediatric, mml-Neurometabolic