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Test Code 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


In addition, the following organic acid disorders can be confirmed by this assay:

-2-Methylbutyryl-CoA dehydrogenase (SBCAD) deficiency

-Isobutyryl-CoA dehydrogenase (IBD) deficiency

Additional Tests

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

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 Acylcarnitine Elevations (also applies to any plasma or serum C5 acylcarnitine elevations) in Special Instructions.

Method Name

FAO: Fibroblasts Incubated with Enriched Medium Followed by Tandem Mass Spectrometry (MS/MS) for Acylcarnitines

CRYOB: Fibroblast Subculture Followed by Cryopreservation and Storage

Performing Laboratory

Mayo Medical Laboratories in Rochester

Specimen Type


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 [T115]).

Specimen Volume: 4-mm punch

Specimen Stability Information: Refrigerated (preferred)/Ambient

Specimen Stability Information

Specimen Type Temperature Time
Tissue Varies

Reject Due To








Specimen in formalin or fixative preservative

Reference Values

An interpretive report will be provided.

Day(s) and Time(s) Performed


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 In Process


Result ID Test Result Name Result LOINC Value
23479 Specimen 31208-2
23480 Specimen ID 57723-9
23481 Source 31208-2
23482 Order Date 82785-7
23483 Reason For Referral 42349-1
23484 Method 49549-9
23485 Fatty Acid Ox Probe Assay, Fibro In Process
23486 Results 35574-3
23487 Interpretation 59462-2
23488 Amendment 48767-8
23489 Reviewed By 18771-6
23490 Release Date 82772-5

Analytic Time

15 to 71 days depending on rapidity of growth


Abnormal results will include a description of the abnormal profile, in comparison to normal and abnormal corun 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 at the Mayo Clinic or elsewhere, and a phone number to reach one of the laboratory directors in case the referring physician has additional questions.


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


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

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 (MS/MS) 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 Laboratory Guide to the Methods in Biochemical Genetics. Edited by N Blau, M Duran, KM Gibson. Springer-Verlag, Heidelberg, 2008)

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 1 enzyme per assay, and molecular assays for common mutations are limited by the frequent occurrence of compound heterozygous patients with uncommon, private mutations that must be distinguished from unaffected carriers. Furthermore, neither specific enzyme assays nor molecular genetic testing is 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.

Specimen Retention Time

3 years-Check with the lab for availability

Genetics Test 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).


This test is not available for prenatal testing.


Please provide clinical information.

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.


1. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (T576) is available in Special Instructions.

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