Antibodies, Actin and Mitochondrial M2

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Antibodies, Actin (Smooth Muscle) and Mitochondrial M2

Synonym/acronym: Antiactin antibody, ASMA; mitochondrial M2 antibody, M2 antibody, AMA.

Common use

To assist in the differential diagnosis of chronic liver disease, typically biliary cirrhosis.


Serum (1 mL) collected in a red-top tube.

Normal findings

(Method: Immunoassay, enzyme-linked immunosorbent [ELISA]) Actin smooth muscle antibody, IgG
NegativeLess than 20 units
Weak positive20–30 units
PositiveGreater than 30 units
Mitochondrial M2 antibody, IgG
NegativeLess than 20 units
Weak positive20.1–24.9 units
PositiveGreater than 25 units


Primary biliary cirrhosis (PBC) is a disease in which the small bile ducts of the liver are destroyed by an inflammatory process. Antimitochondrial antibodies are found in 90% of patients with PBC. Mitochondrial M2 antibody has a higher degree of specificity than any of the other three types of detectable mitochondrial antibodies (M1, M5, M6) for PBC. PBC is identified most frequently in women aged 35 to 60. Testing is useful in the differential diagnosis of chronic liver disease because antimitochondrial antibodies are rarely detected in extrahepatic biliary obstruction, various forms of hepatitis, and cirrhosis. Antismooth muscle antibodies are autoantibodies found in high titers in the sera of patients with autoimmune diseases of the liver and bile duct. Smooth muscle antibodies are directed against the F-actin subunits present in all smooth muscle fibers and are therefore not organ specific. Simultaneous testing for antimitochondrial antibodies can be useful in the differential diagnosis of chronic liver disease.

This procedure is contraindicated for



    Actin antibodies (ASMA)

  • Differential diagnosis of liver disease
  • Mitochondrial M2 antibodies (AMA)

  • Assist in the diagnosis of PBC
  • Assist in the differential diagnosis of chronic liver disease

Potential diagnosis

Increased in

  • The exact cause of PBC is unknown. There is a high degree of correlation between the presence of actin smooth muscle antibodies (ASMA) and mitochodrial M2 antibodies (AMA) with PBC, and PBC therefore is thought to be an autoimmune disease. The antibodies have been identified in the sera of patients with other autoimmune diseases.

  • Actin antibodies (ASMA)

  • Autoimmune hepatitis
  • Chronic active viral hepatitis
  • Infectious mononucleosis
  • PBC
  • Primary sclerosing cholangitis
  • Mitochondrial M2 antibodies (AMA)

  • Hepatitis (alcoholic, viral)
  • PBC
  • Rheumatoid arthritis (occasionally)
  • Systemic lupus erythematosus (occasionally)
  • Thyroid disease (occasionally)

Decreased in


Critical findings


Interfering factors

  • Drugs and substances that may increase mitochondrial M2 (AMA) levels include labetalol (related to liver damage).
  • Drugs and substances that may decrease mitochondrial M2 (AMA) levels include cyclosporine and ursodiol

Nursing Implications and Procedure


  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching:  Inform the patient this test can assist in the diagnosis of liver disease.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s hepatobiliary and immune systems, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
  • Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no food, fluid, or medication restrictions unless by medical direction.


  • Potential complications: N/A
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex,.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis.


  • Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
  • Nutritional Considerations: The presence of antimitochondrial or antismooth muscle antibodies may be associated with liver disease. Dietary recommendations may be indicated and vary depending on the severity of the condition. A low-protein diet may be in order if the liver cannot process the end products of protein metabolism. A diet of soft foods may be required if esophageal varices have developed. Ammonia levels may be used to determine whether protein should be added to or reduced from the diet. Patients should be encouraged to eat simple carbohydrates and emulsified fats (as in homogenized milk or eggs) rather than complex carbohydrates (e.g., starch, fiber, and glycogen [animal carbohydrates]) and complex fats, which require additional bile to emulsify them so that they can be used. Observe the cirrhotic patient carefully for the development of ascites; if ascites develops, pay strict attention to fluid and electrolyte balance.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include albumin, ALP, ammonia, ANCA, ANA, bilirubin, biopsy liver, electrolytes, and GGT.
  • See the Hepatobiliary and Immune systems tables at the end of the book for related tests by body system.
Handbook of Laboratory and Diagnostic Tests, © 2013 Farlex and Partners