SMOOTH MUSCLE ANTIBODY
- SMOOTH MUSCLE ANTIBODY
- Start Date
- Expiration Date
- Antismooth Muscle Antibody; ASMA; SMA
- CPT Codes
- Reference Test
- Transport Info
- Fasting Required?
- Patient Instructions
- Reference Range
If positive, results are titered
ASMA titers greater than 1:40 are significant
Indirect Fluorescent Antibody (IFA).
Differential diagnosis of liver disease. Antismooth muscle antibodies are found mainly in chronic active hepatitis. The antibody is usually not seen in systemic lupus erythematosus. Antismooth muscle antibodies are also seen in acute viral hepatitis and low tiers may be seen in primary biliary cirrhosis.
Smooth muscle antibodies (SMA) may be demonstrated in patients with acute and chronic hepatitis, with the highest titers occurring in chronic active hepatitis (CAH). Various forms of chronic liver disease are associated with low SMA titers (less than 1:160), except for CAH, where titers may reach 1:640 or greater. In most cases, however, CAH titers range from 1:80-1:320 and persist for years. In viral hepatitis, the titers are generally below 1:80 and are transient. Both viral and autoantibody markers may be used to classify different sub-groups of CAH and it has been demonstrated that most HBV antigen-negative patients are SMA positive. Antinuclear antibodies (ANA), SMA, and anti-mitochondrial autoantibodies (AMA) occur in CAH and form the basis of distinguishing different groups of autoimmune hepatitis. CAH patients who are ANA and SMA positive have high titers that are readily demonstrable by immunofluorescent techniques. SMA tests have been helpful in confirming the diagnosis of approximately 70% of the cases of CAH. A positive SMA test helps to rule out systemic lupus erythematosus, as this disease usually tests negative for SMA. It is also found in approximately 50% of patients with primary biliary cirrhosis (titers are low; 1:10-1:40) and in up to 28% of patients with cryptogenic cirrhosis. A high incidence of SMA has also been reported in serum of patients with infectious mononucleosis. Diseases including carcinoma of the breast, malignant melanoma, and ovarian carcinoma have been reported to have SMA. SMA is rarely found (less than 2%) in patients with bile duct obstruction, alcoholic cirrhosis, and in the normal population.