Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (714 page)

   Quantitative measurements of AMA do not reflect on the progression of the disease.

   Five to ten percent of cases of PBC do not have detectable levels of AMA.

   Some individuals with host versus graft disease have measurable levels.

   Although AMAs serve as highly sensitive markers for the diagnosis of PBC, AMAs can frequently be detected in patients with other diseases, such as primary systemic sclerosis, Sjögren syndrome, rheumatoid arthritis, and autoimmune hepatitis.

   The M2, M4, and M8 staining patterns are indistinguishable by immunofluorescence, so specific EIA assays must be used to determine which of these antibodies are present in a positive serum. Anti-M9 antibodies can only be detected by EIA assay.

ANTI–SMOOTH MUSCLE ANTIBODIES (ASM)

   Definition

   Smooth muscle antibodies are directed toward actin, myosin, and occasionally against other contractile proteins in muscle cells. Smooth muscle antibodies can present in a variety of liver disease states. Smooth muscle antibodies can be useful in differentiating liver disease when used in conjunction with other laboratory results and the patient’s clinical symptoms.

   
Normal range:

   IFA: negative; if positive, results are tittered, ELISA: <1:40 titer.

   ASM titers >1:40 are significant.

   Use

   Aids in the diagnosis of chronic active hepatitis

   Differential diagnosis of liver disease