Acetylcholine Receptor (AChR) Antibody
Also known as:Muscle nicotinic Acetylcholine Receptor (AChR) Binding Antibody; AChR Antibody; Myasthenia Gravis Antibodies
Formal name:Acetylcholine Receptor Binding Antibody; Acetylcholine Receptor Blocking Antibody; Acetylcholine Receptor Modulating Antibody
Related tests:Anti-MuSK Antibody, Striated Muscle Antibody, Rheumatoid Factor, Thyroid Panel, Thyroid Antibodies, ANA, Autoantibodies
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Why Get Tested?
To help diagnose myasthenia gravis (MG) and to distinguish between MG and other conditions with similar symptoms
When to Get Tested?
When you have symptoms that suggest MG, such as a drooping eyelid, double vision, difficulty chewing or swallowing, and/or weakness in specific muscles
A blood sample drawn from a vein in your arm
Test Preparation Needed?
How is it used?
An acetylcholine receptor (AChR) antibody test is used to help diagnose myasthenia gravis (MG) and to distinguish it from other conditions that may cause similar symptoms, such as chronic muscle fatigue and weakness.
AChR antibodies hinder the action of acetylcholine, a chemical (neurotransmitter) that transmits messages between nerve cells. The antibodies do this in three major ways:
- "Binding" antibodies attach to the acetylcholine receptors on nerve cells and may initiate an inflammatory reaction that destroys them.
- "Blocking" antibodies may sit on the receptors, preventing acetylcholine from binding.
- "Modulating" antibodies may cross-link the receptors, causing them to be taken up into the muscle cell and removed from the neuromuscular junction.
Three different types of tests are available to determine which of these may be the problem in a particular individual. However, the test that measures "binding" antibodies is most commonly used because it is generally rare for the other two tests to be positive without the "binding" test being positive as well. These other tests may be used when a healthcare practitioner strongly suspects myasthenia gravis and the "binding" test is negative.
One or more of the AChR antibody tests may be ordered as part of a panel of tests that may also include a striated muscle antibody test to help establish a diagnosis. Depending upon results, an anti-MuSK (muscle-specific kinase) antibody test may also be ordered.
People with MG often have an enlarged thymus gland and may have thymomas (typically benign tumors of the thymus). Located under the breastbone, the thymus is an active part of the immune system during childhood but normally becomes less active after puberty. If a thymoma is detected, such as during a chest computed tomography (CT) scan done for a different reason, then an AChR antibody test may sometimes be used to determine whether the person has developed these antibodies.
When is it ordered?
The AChR antibody test may be ordered when a person has symptoms that suggest myasthenia gravis, such as:
- Drooping eyelid
- Double vision
- Decreased eye movement control
- Difficulty swallowing, chewing, with choking, drooling and gagging
- Slurred speech
- Weak neck muscles
- Trouble holding up head
- Difficulty breathing
- Difficulty walking and an altered gait
- Specific muscle weakness but normal feelings/sensations
- Muscle weakness that worsens with sustained effort and improves with rest
An AChR antibody test may sometimes be ordered when a thymoma is detected during an imaging scan.
What does the test result mean?
AChR antibodies are not normally present in the blood. They are autoantibodies and their presence indicates an autoimmune response.
If a person has AChR antibodies and symptoms of myasthenia gravis (MG), then it is likely that the person has this condition.
AChR antibodies may also be positive with some thymomas, in people who are being treated with drugs such as penicillamine, with some small cell lung cancers, with autoimmune liver disease, and with Lambert-Eaton myasthenic syndrome (a condition associated with interference with the release of acetylcholine from the nerve ending).
A negative test result does not rule out MG. Up to 50% of those with ocular MG (affecting only eye-related muscles) and about 10-15% of those with generalized MG will be negative for AChR antibodies. Results from other tests for autoantibodies, such as anti-MuSK (muscle-specific kinase) antibody test and anti-striated muscle antibody test, may aid in establishing a diagnosis. Up to 70% of people suspected to have generalized MG but who are negative for AChR antibodies will be positive for anti-MuSK antibodies.
Is there anything else I should know?
Use of drugs such as succinylcholine can increase AChR antibodies.
People who have MG are more likely to also have other autoimmune disorders, such as rheumatoid arthritis or lupus.
Recent radioactive treatments can interfere with testing.
What is being tested?
Acetylcholine receptor (AChR) antibodies are autoantibodies produced by the immune system that mistakenly target proteins called acetylcholine receptors that are located on skeletal muscle fibers. This test detects and measures AChR antibodies in the blood.
Acetylcholine receptors function as "docking stations" for acetylcholine, a chemical substance (neurotransmitter) that transmits messages between nerve cells. Muscle movement starts when an impulse is sent down a nerve to the nerve ending, where it stimulates the release of acetylcholine. Acetylcholine travels across a microscopic gap between the nerve ending and a muscle fiber at the "neuromuscular junction." When it reaches the muscle fiber, it binds to one of many acetylcholine receptors and activates it, initiating muscle contraction.
AChR antibodies impede communication between nerves and skeletal muscles, inhibit muscle contraction, and cause rapid muscle fatigue by preventing activation of the acetylcholine receptors. They do this in three major ways:
- Binding antibodies attach to the receptors on nerve cells and may initiate an inflammatory reaction that destroys the receptors.
- Blocking antibodies may sit on the receptors, preventing acetylcholine from binding.
- Modulating antibodies may cross-link the receptors, causing them to be taken up into the muscle cell and removed from the neuromuscular junction.
The end result of this interference is the development of myasthenia gravis (MG), a chronic autoimmune disorder associated with the presence of these antibodies and with their effects on muscle control.
AChR antibodies may be detected in different ways to determine which mechanism may be the problem in a particular individual, and the antibodies may be referred to as "binding," "blocking," or "modulating." However, the technique that measures "binding" is the most commonly performed and, generally speaking, it is rare for the other two tests to be positive without the "binding" test being positive as well. These other approaches may be useful when a healthcare practitioner strongly suspects myasthenia gravis and the "binding" test is negative.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
- Should everyone have an acetylcholine receptor (AChR) antibody test?
It is not intended for general screening purposes and most people will never need to have one done.
- Can this test be performed in my healthcare provider's office?
No, it is specialized testing that is not offered by every laboratory. Your blood sample will likely need to be sent to a reference laboratory for testing.
- Can myasthenia gravis (MG) affect my heart?
No, the receptors for heart and smooth (digestive) muscles are different from skeletal muscles so they are not affected by the formation of AChR binding antibodies.
- How serious is MG?
Most people who have it can live a normal or near normal life with treatment and monitoring. One of the most serious complications is a respiratory myasthenic crisis that can occur when muscles that control breathing are weakened. This can be a medical emergency and often requires hospitalization.
- Is there anything I can do to prevent getting AChR binding antibodies?
No, the cause of MG is not known and the condition is not preventable.
- Can MG be passed from one person to another?
MG is not contagious, but a pregnant woman with MG can pass some of her AChR antibodies to her fetus. This can cause a newborn to have MG symptoms for several weeks after birth.
- Can MG be inherited?
As an autoimmune process, no. Some people may inherit a genetic defect that causes congenital myasthenic syndrome, a condition with similar symptoms.
© 2017 American Association for Clinical Chemistry, republished from Lab Tests Online.*
Descriptions of clinical laboratory tests were originally prepared for use on Lab Tests Online, an award-winning patient education website on clinical laboratory testing. Lab Tests Online is produced by the American Association for Clinical Chemistry (AACC), a global scientific and medical professional organization dedicated to clinical laboratory science and its application to healthcare. The Lab Tests Online website is developed in collaboration with other laboratory professional societies and is funded in part through corporate sponsorships.