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Blood Work To Diagnose Myasthenia Gravis

Myasthenia gravis (MG) is diagnosed using a combination of a health history, physical exam, and a variety of tests, including blood tests. Blood tests are an important part of diagnosing and treating myasthenia gravis.1

Blood tests will show whether your body is making any of the antibodies common in people with MG. Antibodies are chemicals made by the body to attack germs like viruses and bacteria or abnormal cells like cancer.

In patients with MG, antibodies attack healthy parts of the body called the neuromuscular junction. The neuromuscular junction is an area between a nerve and muscle where the muscle takes directions from the nerves, telling it to move.

The MG antibodies

People with MG most often make at least 1 of these antibodies:1-4

  • Acetylcholine receptor (AChR)
  • Muscle-specific tyrosine kinase (MuSK)
  • Low-density lipoprotein receptor-related protein 4 (LRP4)

Around 8 out of 10 people with MG will have AChR antibodies in their blood. Only 1 out of 10 will have the MuSK antibodies, and even fewer will have LRP4 antibodies.1

Roughly 6 out of every 100 people with MG will have seronegative myasthenia gravis, meaning they have none of the common antibodies. People with ocular MG are more likely to have seronegative MG.1

As more antibodies for MG are found, new blood tests will be developed, and fewer people will be diagnosed with seronegative MG.2

Nearly all people with MG and a thymoma are positive for antibodies.1

What the antibody test means

The type of antibodies a person with MG has can help doctors decide which treatments are best. For example, the usual treatment options for AChR positive MG may not work for people with MuSK positive MG.2

People with MuSK antibodies tend to have more weakness in the muscles that control swallowing, speaking, and chewing. Doctors call these the bulbar muscles. MuSK MG patients tend to have less eye weakness and more trouble speaking and controlling their facial expressions. They also tend to have neck, shoulder, and breathing weakness.3

Acetylcholinesterase inhibitors may actually make MG symptoms worse in people with MuSK MG, and thymectomy does not improve symptoms.3,4

People with LRP4 antibodies are more likely to be female and have ocular or mild generalized MG. Breathing problems are rare in people with LRP4 antibodies.5

Other things to note

Currently, doctors believe that AChR antibody levels are not connected to how mild or severe a person’s MG is, or how well the person is responding to treatment. This is why your doctor will probably not regularly test your antibody levels, unlike other autoimmune diseases.1

People with MG are more likely to have other autoimmune diseases such as thyroid disease, lupus, multiple sclerosis, or rheumatoid arthritis. Some of these other autoimmune diseases create different antibodies, so blood tests for these conditions may be done too.3

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Written by: Jessica Johns Pool | Last reviewed: March 2021