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HelpTest Code LAB1230211 Filamentous-Actin (F-actin) Antibody, IgG, Serum
Performing Laboratory
Mayo Clinic Laboratories in Rochester
Reporting Name
F-Actin Ab, IgG, SSpecimen Type
SerumSpecimen Required
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Submission Container/Tube: Plastic vial
Specimen Volume: 0.5 mL Serum
Collection Instructions: Centrifuge and aliquot serum into a plastic vial.
Reject Due To
| Gross hemolysis | OK |
| Gross lipemia | OK |
| Gross icterus | OK |
| Heat treated specimens | Reject |
Specimen Stability Information
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum | Refrigerated (preferred) | 21 days |
| Frozen | 21 days |
Specimen Minimum Volume
Serum: 0.4 mL
Special Instructions
Day(s) Performed
Monday
Specimen Retention Time
14 daysReport Available
2 to 8 daysReference Values
Negative: <20.0 U
Weak Positive: 20.0-30.0 U
Positive: >30.0 U
Useful For
Evaluation of patients with hepatitis of unknown origin associated with hypergammaglobulinemia and/or abnormal liver enzymes
This test may also be useful for confirming positivity for smooth muscle antibodies.
Testing Algorithm
For more information First-Line Screening for Autoimmune Liver Disease Algorithm.
CPT Code Information
83516
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 filamentous-actin is enzyme-linked immunosorbent assay. 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 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 DS2 instrument by Dynex.(Package insert: QUANTA Lite Actin IgG ELISA 708785. INOVA Diagnostics; Rev. 6, 11/2018)
Supportive Data
In a study performed at Mayo Clinic, 173 serum samples submitted for clinical testing for anti-smooth muscle IgG antibodies (anti-SMA) performed by indirect immunofluorescence assay (IFA) were collected. These samples were subsequently tested using the anti-filamentous-actin (F-actin) IgG antibody enzyme-linked immunosorbent assay (ELISA). 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(IFA), 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 (AIH), 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 diagnoses other than AIH, 122 were negative (<20.0 units), which corresponded to a specificity of 76.7%. The anti-SMA IFA had a significantly lower clinical sensitivity of 78.6% than the F-actin ELISA with comparable specificity (76.1%). Positivity for either anti-F-actin antibodies or anti-SMA improved the diagnostic sensitivity to 92.9%, although with a decreased specificity of 66.0%. This data indicates that the ELISA for F-actin antibodies may have improved diagnostic utility in comparison to the anti-SMA by indirect immunofluorescence, although a combination of these tests may be useful for some patients.