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Test Code LABFACT F-Actin Ab, IgG, S

Additional Codes

Test Name in EPIC EPIC Test Code Mnemonic Mayo Test ID


Reporting Name

F-Actin Ab, IgG, S

Useful For

Evaluating patients suspected of having autoimmune hepatitis

Method Name

Enzyme-Linked Immunosorbent Assay (ELISA)

Performing Laboratory

Mayo Medical Laboratories in Rochester

Specimen Type


Specimen Required


Preferred: Serum gel

Acceptable: Red top

Specimen Volume: 0.5 mL

Specimen Minimum Volume

0.4 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Refrigerated (preferred) 21 days
  Frozen  21 days

Reject Due To


Mild OK; Gross OK


Mild OK; Gross OK


Mild OK; Gross OK




Reference Values

Negative: <20.0 U

Weak Positive: 20.0-30.0 U

Positive: >30.0 U

Day(s) and Time(s) Performed

Thursday; Evening

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
FACT F-Actin Ab, IgG, S 44706-0


Result ID Test Result Name Result LOINC Value
FACT F-Actin Ab, IgG, S 44706-0

Method Description

The method used to detect antibodies directed against F-Actin is enzyme-linked immunosorbent assay (ELISA). Prediluted controls and diluted patient sera are added to separate wells, allowing any actin antibodies present to bind to the antigen. Unbound sample is washed away and an enzyme labeled anti-human IgG is added to each well. A second incubation allows the enzyme labeled anti-human IgG to bind to any patient antibodies, which have become attached to the microwells and any unbound conjugate is removed by another wash step. The bound conjugate is visualized with 3,3’,5,5’ tetramethylbenzidine (TMB) substrate which gives a blue reaction product, the intensity of which is proportional to a concentration of autoantibody in the sample. Sulfuric acid is added to each well to stop the reaction. This produces a yellow endpoint color, which is read at 450 nm. Testing is performed on the Triturus instrument by Grifols.(Package insert: ELISA Kits, INOVA Diagnostics, San Diego CA)


Serologic tests for autoantibodies, including anti-F-Actin, should not be relied upon exclusively to determine the etiology or prognosis of patients with liver disease.

Supportive Data

In a study performed at Mayo Clinic, 173 serum samples submitted for clinical testing for anti-smooth muscle antibodies (anti-SMA), as performed by indirect immunofluorescence (IIF), were collected. These samples were subsequently tested using the anti-F-Actin antibody ELISA. By using the manufacturer’s cut-offs for the 2 tests (negative at <20.0 units for the F-Actin ELISA and <1:20 titer for the anti-SMA IIF), the 2 tests had an overall concordance of 79.8%. In addition to the analytical concordance, patient histories were abstracted for diagnoses related to liver dysfunction. Of the 14 patients with autoimmune hepatitis, 13 were positive (≥20.0 units) for F-Actin antibodies by ELISA, which corresponded to a sensitivity of 92.9%. Of the remaining 159 patients who had a diagnosis of something other than autoimmune hepatitis, 122 were negative (<20.0 units), which corresponded to a specificity of 76.7%. In comparison, at a clinical specificity of 76.1%, which is similar to the ELISA, the anti-SMA IIF method had a significantly lower clinical sensitivity of 78.6%. Positivity for either anti-F-Actin antibodies or anti-SMA improved the diagnostic sensitivity to 92.9%, although the specificity decreased to 66.0%. This data indicates that the ELISA for F-Actin antibodies may have improved diagnostic utility in comparison to the anti-SMA by IIF, although a combination of these tests may be useful for some patients.


Seropositivity for anti-F-Actin antibodies is consistent with a diagnosis of autoimmune hepatitis (AIH).


A negative result for anti-F-Actin antibodies does not exclude a diagnosis of AIH.


In a study conducted at Mayo Clinic, the F-Actin ELISA had a clinical sensitivity of 92.9% when using the manufacturer’s recommended cutoff of 20.0 U. In addition, the F-Actin ELISA had a clinical specificity of 76.7% when using the aforementioned cutoffs. See Supportive Data.

Analytic Time

1 day

Specimen Retention Time

7 days

Test Classification

This test has been cleared or approved by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

Clinical Information

Autoimmune hepatitis (AIH) is caused by chronic inflammation within the liver, resulting in damage to the hepatocytes.(1) Initially, patients with AIH may be clinically asymptomatic, usually identified only through an incidental finding of abnormal liver function tests. At a more advanced stage, patients may manifest with symptoms such as jaundice, pruritus, and/or ascites, which are secondary to the more extensive liver damage. As implied by the name, AIH has many characteristics of an autoimmune disease, including female predominance, hypergammaglobulinemia, association with specific HLA alleles, responsiveness to immunosuppression, and the presence of autoantibodies. There are several autoantibodies associated with AIH, although the most common is anti-smooth muscle antibody (anti-SMA). Anti-SMAs are generally identified by indirect immunofluorescence using a smooth muscle substrate. The antigen specificity of anti-SMAs in the context of AIH has been identified as filamentous-actin (F-actin).(2) Because the clinical symptoms of AIH are nonspecific, being found in a variety of liver diseases (drug/alcohol-associated hepatitis, viral hepatitis, primary sclerosing cholangitis, etc), the diagnosis can be challenging. A set of diagnostic criteria for AIH has been published, and includes the presence of various autoantibodies, elevated total IgG, evidence of hepatitis on liver histology, and absence of viral markers.(3) The combination of autoantibody serology, specifically anti-SMAs and anti-F-Actin antibodies with liver histology and thorough clinical evaluation are useful in the evaluation of patients with suspected autoimmune hepatitis.