Antibody testing is a highly accurate tool used in the diagnosis of myasthenia gravis (MG). As an autoimmune disease, MG involves the body’s immune system mistakenly developing antibodies that target itself, instead of harmful foreign bodies such as bacteria and viruses. In MG, these antibodies attack the communication between nerves and muscles, causing muscle weakness. As part of the MG diagnostic process, a blood sample is analyzed to check for the presence of antibodies, confirming diagnosis and guiding treatment choices.
The types of antibodies tested for in MG
While there are a number of antibodies targeted in antibody testing for MG, these are the most common antibodies found in people diagnosed with MG.
AChR antibodies
AChR antibodies (acetylcholine receptor antibodies) are the most common and are found in around 80% to 85% of patients with MG. There are three different types: binding, blocking or modulating. Associated symptoms include drooping eyelid, double vision, trouble chewing and swallowing, slurred speech, weak neck muscles, difficulty breathing and holding up the head. Walking can also become difficult.
MuSK antibodies
MuSK antibodies (muscle-specific kinase antibodies) are found in around 5% to 8% of people with MG. Associated symptoms mostly include weakness in the face, neck and breathing muscles.
LRP4 antibodies
LRP4 antibodies (low-density lipoprotein receptor–related protein 4) are less common, and found in around 2% of patients. LRP4 antibody-positive MG often means milder symptoms.
What is seronegative MG?
Seronegative means there are no detectable antibodies, and diagnosis is confirmed by relying on other diagnostic tests. It may also be necessary to redo the antibody testing. Around 10% of patients with MG are seronegative.
Read more about MG testing and diagnosis
The importance of testing for antibodies in MG
Diagnosing MG can be challenging, as symptoms can also apply to other neuromuscular or neurological conditions. Several different diagnostic tests, including symptom assessment, physical examination, blood tests, repetitive nerve stimulation, single-fiber electromyography, imaging and antibody testing are therefore required to confirm diagnosis.
Identifying the antibody is important for determining the correct treatment in MG. Some treatments are only approved for patients who are positive for certain antibodies. Patients who are AChR antibody-positive have the most options.
The monitoring of antibody titers by regularly repeating the antibody tests is also useful in tracking disease progression and response to treatment.
What to expect in antibody testing
Antibody testing is simple and non-invasive. It just requires a blood sample, which is tested in a specialized laboratory. Results can take up to several weeks, depending on the antibody being tested, the laboratory’s workload and your location. Your doctor will go through your results with you and explain what they mean for your diagnosis.
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