Anti-smooth Muscle Antibody Test

What is an anti-smooth muscle antibody test?

Some antibodies attack smooth muscles. An anti-smooth muscle antibody test detects these antibodies that do so by just testing a blood sample.

The immune system functions by producing proteins called antibodies to combat the effect of antigens. Antigens are substances that are harmful to the body. Microorganisms such as viruses and bacteria are covered with these harmful antigens. Each antibody produced is specific for a particular antigen.  A condition called autoimmune disorder occurs when the body accidentally makes antibodies against itself. These are auto antibodies and they end up attacking the normal healthy cells of the body. Anti-smooth muscle antibody test searches for only one kind of autoantibody and that is the one that attacks smooth muscles. Anti-smooth muscle antibodies are present in autoimmune conditions such as liver diseases including autoimmunehepatitis (AIH) and primary biliary cholangitis.

Anti-smooth muscle antibody test
Photo Credit: Healthline

Autoimmune hepatitis

An anti-smooth muscle antibody test is likely to be performed when a liver condition lasts beyond six months. This will help exclude the presence of an active AIH. The commonest cause of hepatitis globally is viruses but AIH is an exception in that the liver damage here is actually caused by an attack by the body’s own immune system.

AIH is a progressive liver condition that may lead to liver cirrhosis or liver scarring and finally liver failure.

Symptoms and signs include:

  • Hepatomegaly, meaning an increase in liver size
  • Abdominal swelling or distension
  • Pains over the right hypochondrium where the liver is
  • Dark-colored urine
  • Clay-colored stools
  • Jaundice, meaning yellowing of the eyes, skin and mucous membranes
  • Pruritus i.e. itching
  • Tiredness
  • Anorexia
  • Nausea and vomiting
  • Pains over joints
  • Abdominal discomfort
  • Skin Rashes

Procedure for an anti-smooth muscle antibody test

It requires no prior preparation. This test can be performed in the hospital, at a clinic or even a laboratory.

A blood sample is needed for the test so a tourniquet is tied to the upper arm to enhance visibility of the veins and ensure easier placement of needles. An adequate vein is located and cleaned with gauze soaked with alcohol/antiseptic to disinfect the site. Needle is then inserted and blood is collected with a tube attached to the needle.

When the blood collected is enough, the tourniquet is untied, the needle removed and a clean gauze or cotton wool placed over the site with slight pressure application. Upon removal of the needle, nothing may be felt or just a slight throbbing may be felt at the site.

Risks associated with an anti-smooth muscle antibody test

The risks involved are very minimal. A little bruising may present at the injection site. This is reduced by applying pressure at the injection site after the removal of the needle for a few minutes. Some people who have clotting disorders may still experience bleeding after the needle must have been removed. Individuals with knowledge of their abnormal blood status or those taking blood thinning medications should inform the doctor before the samples are even taken.

Thrombophlebitis which is an inflammation of veins can occur in rare cases and a warm compress done severally can effectively curb it.

Other rare manifestations that may follow blood drawing include:

  • Dizziness or fainting
  • Excess bleeding
  • Hematoma which means blood collection underneath the skin
  • Infection on the needle site

Interpreting the results of an anti-smooth muscle antibody test

When results come in as normal, it means that a significant amount of anti-smooth muscle antibodies has not been found in your blood. The result is reported in titers. A normal titer range is taken as a dilution less than 1:20.

An abnormal result means that ASMAs are identified in the blood sample. Positive ASMA results are taken as a dilution greater than or equal to 1:40.

A test result that is positive for ASMA apart from being caused by an autoimmune liver disease can also be due to:

  • Cancers like melanoma, breast cancer or cancer of the ovaries
  • Chronic hepatitis C virus infection
  • Infectious mononucleosis

In addition to an anti-smooth muscle antibody test, an F-actin antibody test may increase the sensitivity of autoimmune hepatitis over other conditions. Tests results require interpretation most especially when there is an association with other tests that have been performed thus there is need to talk to a doctor.

A positive diagnosis of AIH implies that your immune system has accidentally made antibodies that attacked healthy liver cells. AIG granted can occur in any gender but there is a greater preponderance with women constituting 70 percent of those that develop it.

Ultimately, AIH can result in:

  • Liver damage
  • Liver cirrhosis
  • Liver cancer
  • Liver failure
  • The need for liver replacement

It is best you consult a doctor as they are able to determine the best treatment modality when necessary and attend to questions where doubts exist.

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