You may be familiar with antibodies as immune system proteins that help protect you from infections. But did you know they also play a role in the liver disease primary biliary cholangitis (PBC)? Your doctor may order antibody testing as part of diagnosing your disease.

In this article, we’ll discuss seven things to know about antibody tests for PBC (formerly primary biliary cirrhosis) and what they tell you. To learn more about your specific case of PBC, talk to your doctor or hepatologist (liver specialist).

1. Antibody Tests Look for Proteins To Help Diagnose PBC

PBC is an autoimmune disease that develops when the immune system attacks the liver. Specifically, it damages the bile ducts — small canals that carry bile from the liver to the small intestine. Inflammation from PBC leads to liver damage, bile buildup, and eventually fibrosis (scar tissue buildup).

When diagnosing autoimmune diseases like PBC, doctors look for antibodies in your body. These proteins normally recognize bacteria and viruses to fight illnesses. People with PBC also have antibodies that mistakenly recognize their own body as foreign. Known as “autoantibodies,” they’re a key marker of autoimmunity.

Autoantibody testing is an important piece of the puzzle in diagnosing PBC. Health experts recommend that anyone who has cholestasis — slow bile flow through the liver — should undergo PBC antibody testing.

2. Your Doctor Will Order a Blood Test To Look for PBC Antibodies

Antibodies travel throughout your body in your bloodstream. Your doctor will order a blood test to check for PBC antibodies. A trained professional will take a small sample from a vein in your arm. Then they will send the sample to a lab for testing.

Indirect immunofluorescence (IIF) is a technique that uses specialized antibodies with fluorescent dyes. The fluorescent antibodies recognize and attach to the antibodies in the blood sample. When you look at the sample under a special microscope, you can see cells with antibodies light up. The amount of fluorescence seen in the sample is reported as the antibody titer. Experts consider a titer of 1:40 or higher when diagnosing PBC. A titer of 1:40 means that antibodies are still detectable when the blood sample is diluted to a ratio of 1 part blood to 40 parts diluent.

Another way to measure autoantibodies is with an enzyme-linked immunosorbent assay (ELISA). In an ELISA, a lab specialist uses a plate with mitochondrial proteins attached to its surface. When a blood sample is added to the plate, any antibodies specific to mitochondrial proteins will bind to these proteins.

The specialist then adds another antibody that recognizes the mitochondrial proteins and has an enzyme attached to it. This enzyme creates a biochemical reaction that changes color if the primary antibodies are present and attached to the proteins. The more intense the color change is, the more antibodies are present.

3. Antimitochondrial Antibodies Are Specific to PBC

Antimitochondrial antibodies (AMAs) are the most common type of PBC antibody. Studies show that around 95 percent of people with PBC have AMAs. You may have heard of mitochondria referred to as the “powerhouse of the cell.” They help your cells make energy.

Doctors look for AMAs because they’re more specific to PBC than other autoantibodies. Researchers have found that only 0.5 percent of people without PBC have AMAs. Another 1 percent of people with other diseases outside the liver have these antibodies as well. This means that if your doctor finds AMAs in your blood, there’s a high probability you have PBC.

4. People Who Don’t Have AMAs May Have Antinuclear Antibodies Instead

Most people diagnosed with PBC have AMAs. However, a portion of those without AMAs have antinuclear antibodies (ANAs) instead. The nucleus is the central part of a cell that holds the DNA, which provides instructions for making proteins. Unlike AMAs, ANAs are found in many other autoimmune diseases. Common examples include lupus and rheumatoid arthritis.

Studies show that around half of people with PBC have ANAs. They are more common in those who don’t have AMAs. However, ANA is considered a less common and less specific antibody for PBC, as ANAs can be positive in other autoimmune diseases. Some myPBCteam members have been tested for less common antibodies like ANAs. One member shared their experience: “The hepatologist I saw last week took blood samples to look for ANA. He’s looking deep in the weeds for obscure antibodies.”

5. Autoantibody Levels Don’t Predict the Severity of Your Disease

Studies show that having a higher AMA level doesn’t mean your disease is more severe. Having any AMAs likely means that you have PBC. However, higher levels aren’t associated with how long your symptoms may last. They also aren’t linked to symptoms like jaundice — yellowing of the eyes and skin. Jaundice is a sign of liver damage from diseases like PBC and hepatitis.

Researchers have found that higher AMA levels don’t correlate with liver enzyme levels either. Doctors measure liver enzymes in your bloodstream to check how well the liver works. People with high levels of alkaline phosphatase (ALP) likely have inflammation and liver damage.

6. Antibody Testing Isn’t the Only Way To Diagnose PBC

To be diagnosed with PBC, a person must meet at least two of the following three criteria:

• Elevated ALP levels that are at least 1.5 times the upper limit of normal
• Presence of AMAs with a titer of 1:40 or higher
• Liver biopsy showing liver damage associated with PBC

Most people diagnosed with PBC have high ALP and AMA levels. However, if you’re negative for AMAs, you may need a liver biopsy to confirm your diagnosis. During a biopsy, your doctor uses a long needle to take a tissue sample from your liver. The sample is sent to a lab to be looked at under a microscope. Specialists look for signs of inflammation, damage in the bile ducts, and fibrosis.

Although a liver biopsy is not required to make a PBC diagnosis, it can be useful for determining a person’s prognosis (outlook) by helping to determine the level of fibrosis or damage/scarring in the liver. Additionally, a biopsy can be helpful when a person with PBC does not respond to therapy.

7. Antibody Test Results Don’t Affect Your Treatment Plan

Studies have found that PBC antibody test results don’t affect treatment plans or responses. Your antibody levels likely won’t affect your prognosis with PBC either. The most important thing is to stick with your treatment plan to help prevent liver damage.

The treatments your care team chooses will depend on your symptoms and how your body reacts to medication. Your doctor may prescribe medications that help bile flow through the bile ducts and into the digestive system.

Untreated PBC can cause progression of the disease, leading to permanent liver scarring that continues to get worse over time and can lead to liver complications and failure. In severe cases of liver damage, you may need a liver transplant. This surgery replaces your diseased liver tissue with healthy tissue from a donor. Liver transplants are typically reserved for people who don’t respond to medications anymore.

Talk to Your Doctor About Antibody Testing for PBC

If you’d like to learn more about antibody testing and how it helps diagnose PBC, talk to your doctor. They can order a blood test to confirm you have PBC and rule out other liver diseases. After your doctor confirms your diagnosis, you can discuss your treatment options. Be sure to stick with your treatment plan to avoid permanent damage and liver failure.

Find Your Team

On myPBCteam, the social network for people with primary biliary cholangitis and their loved ones, more than 1,200 members come together to ask questions, give advice, and share their tips with others who understand life with primary biliary cholangitis.

Have you had antibody testing done to diagnose PBC? Which autoantibodies do you have? Did the test help confirm your diagnosis? Share your experiences in the comments below, or start a conversation by posting on your Activities page.