Explanation

Antimitochondrial antibodies (AMA): what is measured?

Mitochondria are the small energy factories in our cells. This test looks at whether there are antibodies against those mitochondria in the blood. These are autoantibodies: antibodies that the body makes by mistake against its own tissue. The laboratory usually also looks at the variant AMA-M2, which is most strongly linked to liver disease.

What can it detect?

Support when primary biliary cholangitis (PBC) is suspected, a chronic inflammation of the small bile ducts in the liver
Distinguishing between the different autoimmune diseases of the liver, together with other antibodies such as ANA and antibodies against smooth muscle

Result

What does the result mean?

Positive result

A positive result means that antibodies against mitochondria were found. According to the Dutch Society for Clinical Chemistry (NVKC), this is not enough to diagnose primary biliary cholangitis: the result must be combined with the symptoms, with liver values such as alkaline phosphatase and gamma-GT, and with testing for viruses that can cause liver inflammation. In people with PBC, these antibodies are found in more than 90 in 100, and AMA-M2 is a strong indication. Other conditions can also give a positive result, such as lupus (SLE), autoimmune inflammation of the thyroid and some infections including syphilis. Symptoms that may fit PBC are itching, tiredness and, in the long run, jaundice, but the condition often starts without symptoms.

Negative result

A negative result makes primary biliary cholangitis less likely. The condition is not completely ruled out: a small proportion of people with PBC have no detectable antibodies against mitochondria, and then other antibodies or a liver biopsy are needed. With abnormal liver values without these antibodies, the doctor looks further for other causes, such as a viral infection, alcohol, medicines or fatty liver.

After an abnormal result

With a positive result, the GP usually first has the liver values measured or repeated, including alkaline phosphatase, gamma-GT, ALAT and bilirubin. If these are abnormal, referral follows to a gastroenterologist or internist (specialist in internal medicine) for an ultrasound of the liver and sometimes a liver biopsy. With normal liver values, treatment is usually not started and the doctor sometimes chooses to monitor the liver values over time.

Reliability

How reliable is the test?

The result is mainly meaningful with abnormal liver values that fit blocked small bile ducts. In people without symptoms and with normal liver values, the chance of the disease is very small, and a positive result is then much more often false-positive than correct. Some people with a positive result never develop liver disease. The result can only be interpreted together with the liver values and the clinical picture.

What can affect the result?

Other autoimmune diseases, such as lupus and autoimmune inflammation of the thyroid, and infections such as syphilis can give a positive result.
Laboratories use different methods; one measures all antibodies against mitochondria, another only the variant AMA-M2. Results therefore cannot simply be compared.
A positive result says nothing about how advanced the liver disorder is; liver values, an ultrasound and sometimes a biopsy are needed for that.
A small proportion of people with primary biliary cholangitis have no detectable antibodies against mitochondria.

Who it is for

Who is the test useful for?

Useful for

Useful with abnormal liver values that fit a problem with bile drainage, especially a raised alkaline phosphatase and gamma-GT, or with long-lasting itching without a skin condition together with tiredness. Also for working out which form of autoimmune liver disease someone has. In people without symptoms and with normal liver values, the predictive value is low and a positive result says little.

How common is it?

Primary biliary cholangitis is rare and mainly occurs in women between 40 and 60 years of age. According to the Dutch Society for Clinical Chemistry (NVKC), the condition often starts gradually; because the liver has a large reserve, it can take years before symptoms appear. A positive result is more common than the disease itself.

NVKC, allesovertesten.nl; no Dutch incidence figure for PBC has been checked

Drawbacks and risks

A positive result without abnormal liver values does occur and can lead to unnecessary worry about a chronic liver disease and to repeated testing without anything being found.
A negative result does not rule out autoimmune liver disease and can therefore give false reassurance with abnormal liver values.

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