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AChR, anti-acetylcholine receptor antibody
This test measures the concentration of a substance called acetylcholine receptor (AChR) antibody in your blood.
AChR antibodies stop the neurotransmitter acetylcholine from doing its job. Acetylcholine carries nerve signals that tell your muscle cells to contract. AChR antibodies are made if you have the rare autoimmune disease myasthenia gravis (MG). People with MG usually, but not always, have a high concentration of AChR antibody.
MG occurs in five to 14 people per 100,000. MG can affect people of any age, but it's most common in women younger than 40 and men older than 60. It's not contagious, although sometimes the newborn baby of a mother with MG can show symptoms for a few weeks that disappear with treatment.
Most people with the disorder have a normal life span but need treatment to control its debilitating symptoms. These often include shortness of breath; trouble using normal speech; drooping eyelids; an unsteady walk; and weakness in the arms, legs, neck, and fingers.
You might have this test if your doctor suspects that you have MG. Symptoms of MG can range from problems with breathing muscles to weakness of muscles throughout your body. The most common symptoms are weakness in muscles that control:
Eye and eyelid motion, found with ocular MG
Chewing and swallowing
Arm and leg motion
Your doctor may also order these tests to check for MG:
Muscle-specific receptor tyrosine kinase (MuSK). The MuSK antibody may be found in 30 to 40 percent of people with MG who do not have AChR antibody.
Edrophonium chloride. This drug may temporarily ease muscle weakness caused by MG. Therefore, it can be used to help diagnose MG.
Repetitive nerve stimulation, or RNS. This is used to test the strength with which muscles respond to low-frequency nerve stimulation. People with MG are likely to have a progressively weaker response as the nerve stimulation continues.
Single fiber electromyography (SFEMG). People with MG and certain other disorders respond to the electrical stimulation of this test with "muscle jitter" – an unsteady, jittery contraction. If you have a normal SFEMG test in a weak muscle, it means that something other than MG is causing the weakness.
Imaging scans. CT or MRI scans can be used to diagnose thymoma, a tumor of the thymus gland sometimes associated with MG.
Lung function tests. These measure the strength of the muscles involved in breathing.
Genetic testing. This can help confirm the diagnosis, although the genes are not found in all people with MG.
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
This test can confirm but not completely rule out MG.
If you have a higher concentration of AChR antibody, it means that you may have MG. Even with a normal level, it's still possible that you have MG. Up to 85 percent of people with MG who have general muscle weakness have AChR antibody. In addition, about half of people with MG around the eyes have the antibody.
The test requires a blood sample, which is drawn through a needle from a vein in your arm.
Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.
Timing is important. Having anesthesia or muscle relaxants for surgery within 48 hours of the test may give a false-positive result.
You don't need to prepare for this test.