When you have a chronic condition like myasthenia gravis (MG), getting blood tests isn’t out of the ordinary. Your blood chemistry can tell you a lot about your health, and specific blood tests are important for confirming a diagnosis.

To understand how these blood tests work, and how they can help with diagnosing MG, you’ll have to understand what they look for. In this article, you can learn about what myasthenia gravis blood tests measure and when you may need them.

Understanding Antibodies

Blood tests for myasthenia gravis are also called serologic tests. Serologic tests evaluate your blood serum, which is the clear fluid left behind after blood cells and platelets are removed. In the case of MG, these tests measure specific antibodies in your blood. Antibodies are proteins in your blood that function as part of your immune system.

Imagine your blood as a busy city. One of the important workers in this city is called an antibody. Antibodies are like tiny security guards that patrol your blood, looking for anything that shouldn’t be there, like allergens, germs, and toxins that can cause harm. Your immune system creates custom antibodies after detecting these unwelcome substances. Each antibody is made to find and destroy something specific. Tests for MG look at these antibodies.

What Are Autoantibodies?

Sometimes, these security guards (antibodies) make a mistake. They start attacking the good parts of your body, like healthy tissues. These mistaken antibodies are called autoantibodies. They’re not protecting you from anything harmful or invasive. Your immune system creates them by mistake. While researchers aren’t exactly sure why the immune system makes autoantibodies, we know they’re often created in response to triggers like infections, exposure to toxins, or genetic mutations (changes). Some autoantibodies are produced spontaneously or without a clear trigger.

If your AChR antibody blood test shows an abnormal result, it means that you have the AChR antibody.

Autoantibodies are active in people with autoimmune diseases like myasthenia gravis. Your doctor can find autoantibodies in your blood using blood tests to diagnose or evaluate autoimmune diseases.

How Blood Tests for Myasthenia Gravis Work

Blood tests for myasthenia gravis measure specific autoantibodies in your blood that are associated with MG. Your neurologist may suggest a blood test after a physical exam if you have muscle weakness consistent with MG.

Most people with MG have autoantibodies that block receptors for acetylcholine (ACh), which is a chemical that helps your nerves and muscles communicate so your muscles can contract. Other MG antibodies affect neuromuscular junctions in other ways. A neuromuscular junction is where a nerve sends signals to a muscle, telling it when to move.

Acetylcholine Receptor Antibody Blood Tests

One important autoantibody the test looks for is called the acetylcholine receptor (AChR) antibody. Acetylcholine is like a messenger that carries signals between your nerves and muscles by releasing from nerves and binding to AChR in muscle fiber. Myasthenia gravis blood tests measure AChR antibodies, which attach to Ach receptors to block communications between nerves and muscles. If your levels of these antibodies are higher than typical levels of abnormal antibodies, you may have MG. Not all people with MG have high levels of AChR antibodies, but most do.

Muscle-Specific Receptor Tyrosine Kinase Blood Tests

Another myasthenia gravis blood test measures the muscle-specific receptor tyrosine kinase (MuSK) antibody, which is an autoantibody that can also interfere with nerve and muscle communications. Even if blood tests don’t detect higher-than-average AChR antibodies, high levels of the MuSK antibody can indicate you have MG. Thirty percent to 40 percent of people with MG who don’t have the AChR antibody have MuSK antibodies.

Normal Ranges for MG Blood Tests

A normal range for an AChR antibody test is either no antibodies or less than 0.05 nanomoles per liter (nmol/L). Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

If your AChR antibody blood test shows an abnormal result, it means that you have the AChR antibody. An abnormal result with symptoms of MG can lead to an MG diagnosis. However, about 1 in 5 people with myasthenia gravis don’t have this antibody. Therefore, a normal result doesn’t rule out MG. If you have a normal result from the AChR antibody test, your doctor might suggest the MuSK blood test next.

Between 6 percent and 10 percent of people with MG have neither AChR antibodies nor MuSK antibodies.

Like AChR antibodies, MuSK antibodies aren’t normally present in the blood. So, if your blood test shows these antibodies, you may have MG. That said, a negative result doesn’t necessarily mean you don’t have MG.

Your antibody test results can tell you which type of myasthenia gravis you have. Between six percent and 10 percent of people with MG have neither AChR antibodies nor MuSK antibodies. This is called double-seronegative myasthenia gravis, as the two main antibody tests for MG have shown negative results. People with seronegative myasthenia gravis are more likely to have ocular myasthenia gravis — mainly affecting the eyes — than those who have the AChR or MuSK antibodies.

If you’ve tested negative for AChR and MuSK antibodies, your neurologist might recommend tests for other autoantibodies such as LDL-receptor-related protein (anti-LRP4) or anti-striated muscle antibody.

One MGTeam member described their diagnostic experience after testing negative for common MG autoantibodies. “None of my bloodwork was positive, but I was diagnosed on the basis of symptoms, nerve conduction studies, and response to pyridostigmine (Mestinon).”

What To Expect During Your MG Blood Test

Getting autoantibody blood tests for MG is similar to getting any other blood draw at the doctor’s office. A trained healthcare provider draws a blood sample from a vein in your arm through a needle.

Be sure to tell your provider about any medications or supplements you’ve taken before your blood test as some can affect the results. Anesthesia or muscle relaxants can lead to false-positive autoantibody test results, so you should wait at least 48 hours after taking them or getting them for surgery to get your MG blood test.

How Blood Test Results Guide Treatment

The type of autoantibodies your MG blood tests detect can help guide your treatment for myasthenia gravis. If you have MuSK antibodies, for example, you may respond differently to specific medications than someone who doesn’t have those antibodies but has high levels of AChR antibodies instead.

While recommending treatment, your doctor considers your antibody blood test results alongside other factors like your age, symptom severity, and your condition’s impact on your quality of life.

When To Get Myasthenia Gravis Blood Tests

A neurologist might use blood tests to look for antibodies associated with myasthenia gravis after a physical exam if you have MG symptoms. MG can cause muscle weakness around the eyes and throughout the body, which can lead to:

• Ptosis (droopy eyelids)
• Diplopia (double vision)
• Arm weakness
• Shortness of breath
• Trouble with speech
• Leg unsteadiness or weakness

Alongside blood tests, your neurologist may use other tests to diagnose myasthenia gravis including a bedside neurological exam, electrodiagnostic tests, lung function tests, or imaging tests of the thymus gland. Electrodiagnostic tests — the most common of which is electromyography (EMG) — check how well your nerves send signals to your muscles.

Getting a diagnosis of myasthenia gravis can take time and patience, as MGTeam members have noted, especially when it’s seronegative MG. “My diagnosis was not confirmed until I had an EMG. My neurologist was convinced at the first visit that I had MG, but the blood work did not confirm this. It took the EMG.” Another said of their MG, “It took me three years to get diagnosed. Patience is the word.”

Talk With Others Who Understand

MGTeam is the social network for people with myasthenia gravis and their loved ones. On MGTeam, members come together to ask questions, give advice, and share their stories with others who understand life with myasthenia gravis.

Have you gotten bloodwork done for myasthenia gravis? Share your experience in the comments below, or start a conversation by posting on your Activities page.