Background

AMA are autoantibodies. They are made up of immunoglobulins. They are produced against mitochondria in liver cells. AMA antigens are present in the different 9 forms: M1 to M9. M2 and M9 are the main cause of disease. To confirm the primary biliary cirrhosis (PBC), M2 form is very important evidence. Many laboratories suggest AMA-M2 test for the confirmation. 

 The AMA test or AMT (antimitochondrial antibody test) is used to check AMA level in the blood. PBC is an autoimmune disease. It can be diagnosed by checking AMA level in the blood via AMT. PBC is a chronic condition. It inflames and scars the bile ducts in the liver. It is slowly developing disease. This can lead to liver damage and bile duct obstruction. Due to blockage of the bile ducts and accumulation of toxic substances in the liver lead to irreversible cirrhosis. Female who are affected by PBC are in the age of 35 to 60. Patients with PBC has the increased level of AMA titer of about 90 to 95%. 

AMA targets lipoic acid which contains epitopes. AMA particularly targets the E2 subunits of 2- oxo acid dehydrogenase complexes (PDC-E2). In the inner surface of the mitochondria, there are many antigens are present. AMA can also target those antigens but till now its diagnostic and therapeutic value is not known. At earlier, AMA was identified as a non-organ specific ATP-ase associated antigen known as M2. It was made of polypeptides which contains mitochondrial enzymes. The 2-oxoacid dehydrogenase (2-OADC) family contains 2 enzymes: E2 subunits of the branched-chain PDC-E2 and 2-oxo-glutarate dehydrogenase complex. Protein X (PDC-E3 binding protein or PDC-E3BP) is the substance of the PDC that copurifies with E2. 

To detect the presence of AMA in blood. An enzyme linked immunosorbent assay is used. It utilizes a cloned recombinant variant of PDC. The alternate method which is also used is immunofluorescence assay. The most recommended method is EIA.  

Indications/Applications

The AMA test is performed to diagnose PBC, autoimmune disease or abnormalities in the liver function. 

The AMA test is performed if you have symptoms like: 

Abdominal pain 

Dryness in the eyes   

Chronic itchy skin (pruritus) 

Dry mouth  

Fatigue 

Loss of appetite 

Nausea 

Yellow eyes  

Yellow skin 

Pain in the muscles and joints 

Weight loss 

Fluid buildup around the ankles, feet or abdomen  

To diagnose PBC, two of the conditions which are listed below must be satisfied. 

Two of the following three criteria must be met to diagnose PBC likely: 

Positive result of serum AMA test and titer value should be more than 1:40. 

Evidence of asymmetric intrahepatic bile duct damage 

Liver enzyme cholestatic pattern for more than six months 

The AMA test is a part of a laboratory evaluation for patients with hepatobiliary diseases. It is conducted to check whether it is confirmed or suspected. The symptoms include like fatigue, itching, increased levels of transaminase, alkaline phosphatase (ALP) and hyperbilirubinemia. In such a situation, laboratory tests of metabolic diseases, viral or drug induced hepatitis and autoimmune disease will be also performed. 

Clinical Significance 

The AMA test is important because normal people do not have any antibodies, about 90 to 95 % of patients have positive AMA test result in the PBC condition, it is an added advantage in autoimmune disease like systemic lupus erythematosus, thyroiditis, rheumatoid arthritis, and scleroderma, AMA level will be decreased in the liver diseases.   

About 5 to 10 % are the cases in which there are negative result of AMA test in PBC conditions. Positive result of serum AMA test is the strong evidence of individual has PBC or under risk in coming years. It is necessary to note that there is no correlation of quantitative assessment of AMA and the prognostic significance of the disorder.   

Patients with end stage of PBC and had transplant the liver shows slightly decreased level of serum AMA. It can be normal within the initial year after the transplantation. Patients who are suffering from the fulminant hepatic failure has the reduced level of blood AMA. This condition occurs due to hepatitis A, hepatitis B and drug induced liver damage. 

Reference Range

One marker of PBC is the presence of AMA in serum. 

The normal result of the AMA test is absence of the AMA. The titer value should be more than 1:5 or less than 0.1 units. 

Interpretation

After the elimination of liver disease causes, a positive result of AMA test with M2 form indicates a chronic cholestasis. It strongly indicated PBC. In the PBC, AMA level in serum increased. The titer value is more than 1:40.  

Collection And Panels

Collection: 

Sample type: Serum 

Sample collection method: Transfer serum into a red top tube by centrifuging blood. 

Container: Red top tube 

Sample volume: 1 ml (minimum 0.5 ml) 

Storage and transport instructions: Refrigerate the sample at 2°C to 8°C. 

Sample stability: The sample is stable at room temperature for 8 hours and in a refrigerator for 7 days. 

Rejected sample conditions: Plasma, hemolysis, heat-treated specimen. 

Method used: Enzyme immunoassay (EIA) 

Panels: 

Other tests which are included: Albumin, Antinuclear antibodies (ANA), Alkaline phosphatase (ALP), Bilirubin, C-reactive protein (CRP), GGT, IgM level, Prothrombin time (PT), Smooth muscle antibodies (SMI) 

References

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8480115/ 

https://pubmed.ncbi.nlm.nih.gov/21529926/