Understanding myasthenia gravis blood tests
Fact-checked by Blood tests are a key step in diagnosing myasthenia gravis (MG), an autoimmune condition characterized by muscle weakness and fatigue.
In MG, the immune system produces abnormal self-reactive antibodies that target proteins needed for nerve-muscle communication, affecting the muscles that support voluntary movement and breathing.
For most people, a blood test to detect these antibodies, along with typical disease symptoms, can confirm an MG diagnosis. The specific type of disease-causing antibodies in MG may also influence treatment and care decisions. However, a negative MG antibody test doesn’t necessarily rule out the disease, and additional tests are sometimes needed.
Main blood tests for myasthenia gravis
The main blood tests for MG are designed to detect known disease-causing antibodies, including those that target:
- acetylcholine receptor (AChR)
- muscle-specific kinase (MuSK)
- low-density lipoprotein receptor-related protein 4 (LRP4)
Each of these proteins facilitates nerve-muscle communication, so their loss in MG impairs proper muscle function. AChR-targeting antibodies are the most common, occurring in about 80%-85% of people with generalized MG and 50%-70% with ocular MG. A smaller number of people have anti-MuSK antibodies (about 5%-8%) or anti-LRP4 antibodies (about 1%-5%).
AChR antibody tests are often done first, followed by a MuSK antibody test if the initial test was negative. If both tests come back negative but MG is still suspected, doctors may recommend follow-up testing for LRP4 antibody-related MG, a more recent discovery. The specific antibodies present help doctors identify disease types.
What if blood tests are negative?
About 10% of people with MG are seronegative, meaning they test negative for common disease-causing antibodies despite having characteristic MG symptoms. This means that a negative blood test result doesn’t necessarily rule out MG.
Because blood tests play an important role in diagnosing MG, seronegative cases are more difficult to confirm. In these cases, doctors may recommend additional MG diagnostic tests, including:
- a thorough neurological exam
- ice pack tests, which can assess if droopy eyelids are related to MG muscle weakness
- repetitive nerve stimulation and single-fiber electromyography, which evaluate nerve and muscle function
- imaging scans, to detect problems in the thymus gland that may be linked to MG
Follow-up blood tests are also often recommended, because some people who test negative eventually test positive. A more sensitive type of blood test, called a cell-based assay, may also detect antibodies in a person initially thought to have seronegative MG based on standard blood tests.
Understanding your results
Diagnosing MG can be complex, so patients should always consult with their doctors for a personalized interpretation of their MG blood test results.
Generally, a positive result identifying known disease-causing antibodies is a strong indicator of MG in a person with typical symptoms. However, blood tests are just one part of the MG testing process, and doctors may run other tests to be sure.
The specific antibody type can help predict how the disease will progress and which treatments will be most effective. However, the levels and types of antibodies don’t always correspond to symptom severity.
A negative MG blood test could mean that a person:
- has seronegative MG
- does not have MG, and something else is causing their symptoms
- has MG-causing antibodies that were not detected
A careful review of symptoms and follow-up testing can help doctors determine which explanation is more likely.
What to expect from the test
For MG lab tests, patients can expect to provide a blood sample for analysis. During the test, a healthcare provider will:
- insert a small needle into a vein
- collect a blood sample in a vial or test tube
- label the sample and send it to a lab for testing
The blood collection process usually takes only a few minutes, but it could take days to weeks for the lab to send the test results back to the doctor, depending on the clinic and specific test type. If a positive result is returned, individuals will work with their doctors to determine which additional tests are needed and to determine a care plan for living with MG.
Myasthenia Gravis News is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.
