Diagnostic Use
Autoimmune diseases are classified as either “tissue or organ specific” or as “non organ specific”. The first group are diseases such as thyroiditis, myasthenia gravis, diabetes mellitus, Addison disease. Some non-organ specific diseases are systemic lupus erythematosus, rheumatoid arthritis and progressive systemic sclerosis. The latter group is an autoimmune response to antigens common to various organs and tissues in the body whereas the former is an autoimmune response to antigens present in only one particular tissue or organ.
Smooth Muscle Antibodies
80 – 90% of patients with chronic active hepatitis develop smooth muscle antibodies along with a positive ANA result and raised IgG level. Titres greater than 1:160 are rarely found in other disorders. 10 – 50% of patients with primary biliary cirrhosis have low titres of smooth muscle antibodies. 60% of patients with viral hepatitis develop these antibodies for a transient period, as do 80% of patients with infectious mononucleosis, RA, alcoholic liver disease and variety of malignancies. 2% of normal population have smooth muscle antibodies related to recent viral infections.
Interpretation
Titre significance
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Titre
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Significance
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| Negative |
Strong evidence against some common tissue?specific Autoimmune and non-organ specific diseases.
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1:40 – 1:80 for PCA, AMA, Adrenal, SMA
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A positive result in this titre range is regarded as being of borderline significance. Note: A repeat specimen should be tested in 2 weeks to check if there is an increase in titre.
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1:160 or greater
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A positive result in this titre range is of significance.
High SMA commonly seen in CAH. High ADR in idiopathic Addisons. High AMA commonly seen in PBC. High PCA commonly in P.A and chronic gastritis. High SAL in Sjogren syndrome with or without sicca complex.
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Reference Intervals
Negative: L80
Positive: 80 – G1280
A positive result in titre range 1:40 – 1:80 is regarded as being of borderline significance.
Note: A repeat specimen should be tested in 2 weeks to check if there is an increase in titre.
A positive result in titre range 1:160 or greater is of significance.
High SMA is commonly seen in CAH.
Test Method
Indirect Immunofluorescence Assay (IFA) - automated
HTZ robotic processing
Manual LED microscopy visual evaluation
Limitations / Interference
Grossly haemolysed and/or high lipaemic serum specimens.
Uncertainty of Measurement
Accepted variation for reported titres is +/- a single doubling dilution.