The antimitochondrial antibody (AMA) test is one of many tests that are used to diagnose primary biliary cholangitis (PBC). Measured via a simple blood draw, AMA testing is a quick and easy way to determine whether you may have PBC.
What are antimitochondrial antibodies?
AMAs are proteins that are produced by the body to attack mitochondria, which are often described as the “powerhouses” of the cells. The mitochondria are responsible for producing the energy that your body needs to function.
In patients with PBC, AMAs tend to attack the mitochondria of cells that make up the liver’s bile ducts, leading to liver dysfunction.
Upwards of 95% of patients with PBC will test positive for AMAs, making it one of the key diagnostic markers for the disease. In fact, the three major criteria for diagnosing PBC include at least two of three of the following:
- AMA positivity.
- Evidence of cholestasis (reduced bile flow), which can be measured by increased alkaline phosphatase levels.
- Evidence of bile duct inflammation.
Read more about PBC testing and diagnosis
Do your AMA levels matter?
Usually, your doctor will be more concerned with the presence or absence of AMAs rather than the specific level of antibodies. An AMA titer of 1:40 is considered positive. This means that the blood sample still tested positive for AMAs after being diluted 40 times.
If you see a higher titer on your report, like 1:160 or 1:320, don’t be concerned. A high number doesn’t necessarily mean a worse prognosis. Depending on the equipment a particular lab uses, the measured AMA level can vary widely and isn’t a good indicator of disease severity or prognosis.
Does a negative AMA test rule out PBC?
Although uncommon, some individuals with PBC will test negative for AMAs. Usually, these patients will test positive for other antibodies linked to PBC, including:
- Antinuclear antibodies
- Anticentromere antibodies
- Anti-multiple nuclear dot antibodies
Other antibodies, including anti-KLHL12 and anti-HK1, have also emerged as potential markers of PBC. If a person tests negative for all of these antibodies, though, PBC is highly unlikely.
Does a positive AMA test by itself confirm PBC?
Usually, a positive AMA test is associated with PBC. However, patients with other autoimmune diseases such as Sjögren disease, systemic sclerosis or systemic lupus erythematosus might also be AMA-positive.
These conditions can coexist in patients with PBC, meaning a positive test could be indicative of multiple autoimmune conditions. This is why AMA positivity on its own is not enough to diagnose PBC.
A variety of other tests, including liver imaging, biopsy and liver function tests should also be performed. These can provide a better overall picture of your liver health and may reveal signs that can help confirm a PBC diagnosis.
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