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Blood Test Tracker

Anti-Smooth Muscle Antibody (ASMA) titer

Looks for antibodies that react with smooth muscle proteins. Mostly used when checking for autoimmune hepatitis, a liver condition. Reported as a titer.

AI-verified against cited sources. Awaiting expert reviewAlso called ASMA, Anti-SMALOINC 8095-2

What it is

Smooth muscle antibodies are autoantibodies, which means your immune system makes antibodies against your own proteins. They mainly react with proteins such as actin, which are found in smooth muscle but also in liver cells. Labs add your blood to a slide of tissue and look for staining. They keep diluting the blood until the staining disappears. The titer is that dilution, such as 1:40 or 1:160. A higher second number means more antibody.

Why it matters

Clinicians use this test with an antinuclear antibody (ANA) test, immunoglobulin G (IgG) and liver blood tests when they are looking at autoimmune hepatitis, a condition where the immune system attacks the liver. Smooth muscle antibodies are found in about half to two-thirds of people with the most common type (type 1). But they are not specific. They also occur with other liver conditions and some infections. A negative result does not rule out autoimmune hepatitis, because about 1 in 7 people with it have no detectable autoantibodies when first tested.

If it’s high

A positive result means smooth muscle antibodies were found in your blood. Higher titers are more suggestive of autoimmune hepatitis, but they cannot confirm it. Low titers are less specific and are sometimes repeated. Your clinician reads the result with your liver tests, IgG level, ANA and sometimes a liver biopsy.

Common causes

  • A low titer with no known condition
  • Chronic hepatitis C or other viral hepatitis
  • Infectious mononucleosis
  • Fatty liver disease
  • Autoimmune hepatitis type 1
  • Primary biliary cholangitis, an autoimmune disease of the bile ducts
  • Other autoimmune conditions or certain cancers

What can help

  • Ask your clinician how this result fits with your liver blood tests, your IgG level and your ANA
  • Ask whether other liver antibody tests or imaging could help
  • Bring a list of your medicines and supplements, since some can affect the liver

What can affect your result

  • Infections such as hepatitis C and infectious mononucleosis
  • Other liver conditions, such as primary biliary cholangitis or fatty liver disease
  • Method: the lab, the tissue used on the slide and how the slide is read can change the titer
  • Hemolyzed, severely lipemic or contaminated samples can be rejected or give unreliable results (ARUP specimen requirements).
  • Methods differ. Labs read stained tissue slides under a microscope, using rat tissue or human HEp-2 cells, so titers and cutoffs can differ from lab to lab.
  • Some infections, such as hepatitis C and infectious mononucleosis, can cause a positive result without autoimmune hepatitis.

Slow. It is not a short-term marker. In one study of people treated for hepatitis C, titers fell after the infection was cleared.

When to talk to a clinician

A positive smooth muscle antibody result is not an emergency by itself. Contact your clinician soon if you notice yellow skin or eyes, dark urine, pale stools, ongoing upper belly pain, or unusual tiredness with nausea or loss of appetite. Call 911 or your local emergency number if you vomit blood, have severe belly pain, or feel confused or very drowsy.

Questions you could ask

  • Why was this test ordered for me?
  • How does this result fit with my liver blood tests and my IgG level?
  • Could another condition, such as a recent infection or fatty liver, explain it?
  • Should we check other liver-related antibodies or repeat this test?

Questions people ask

Does a positive smooth muscle antibody mean I have autoimmune hepatitis?

Not by itself. Higher titers are more suggestive, but the antibody also appears with other liver conditions and some infections. Your clinician looks at your liver tests, IgG level, ANA and sometimes a biopsy before deciding what it means.

What does the titer number mean?

The lab dilutes your blood step by step and finds the last dilution that still shows staining. A result of 1:160 means staining was still seen after the blood was diluted 160 times. Higher second numbers mean more antibody. Labs differ in which titers they call weak or strong, so use the call printed on your report.

My result is negative. Does that rule out autoimmune hepatitis?

No. A negative result makes the most common type less likely, but some people with autoimmune hepatitis have no detectable antibodies, or have other antibodies that are not part of this test. Your clinician decides if more testing is needed.

Show the science and sources

For clinicians and researchers

ASMA is detected by indirect immunofluorescence on rat triple tissue or HEp-2 cells. Targets include filamentous actin (F-actin) and other cytoskeletal components such as vimentin and desmin; a separate ELISA measures anti-actin antibodies (tracked as anti-actin). The British Society of Gastroenterology 2025 guideline reports SMA in 52 to 69% of type 1 AIH, notes that SMA are not specific for AIH, and cites ANA or ASMA positivity in 14 to 19% of metabolic dysfunction-associated steatotic liver disease and ASMA in 20 to 30% of primary biliary cholangitis; co-occurrence of ANA and SMA is more specific, and about 15% of AIH patients have no autoantibodies at presentation. In the International Autoimmune Hepatitis Group simplified criteria, ANA or SMA titer is one of four scored categories (with IgG, histology and exclusion of viral hepatitis), with higher titers scoring more points; a score of 6 or more suggests probable and 7 or more definite AIH. ARUP Laboratories reports the IgG titer with a reference of less than 1:20, a weak positive at 1:20 to 1:80 (repeat in two to three weeks) and a positive at 1:160 or more; its table also lists 1:20 as negative, so 1:20 is shown here as borderline. Mayo Clinic Laboratories reports a screen as negative or positive and titers positive screens as a reflex.

LOINC 8095-2 (primary), 5358-7, 47977-4, 26971-2. Specimen: serum.

Sources

  1. Smooth Muscle Antibody, IgG Titer (test 0051244), ARUP Laboratories
  2. Autoimmune Liver Disease Panel, Serum (test ALDG2), Mayo Clinic Laboratories (catalog mirror at testcatalog.org)
  3. Smooth Muscle Antibody Titer, Serum (test SMAT), Mayo Clinic Laboratories (catalog mirror at testcatalog.org)
  4. Smooth Muscle Antibody (SMA) Test: MedlinePlus Medical Test, MedlinePlus (National Library of Medicine) (2024)
  5. British Society of Gastroenterology guidelines for diagnosis and management of autoimmune hepatitis, Gut (2025)
  6. Simplified criteria for the diagnosis of autoimmune hepatitis, Hepatology (International Autoimmune Hepatitis Group) (2008)
  7. Prevalence and Outcome of Serum Autoantibodies in Chronic Hepatitis C Patients Undergoing Direct-Acting Antiviral Treatment, Frontiers in Immunology (2022)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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