Acetylcholine Receptor (AChR) antibody

You don’t need to do anything special to prepare for this test. You can eat and drink normally beforehand. 

The test uses a blood sample taken from a vein in your arm. 

This is a specialised test that your sample will likely be sent to a reference laboratory. Results usually take about 21 working days. 

This test looks for abnormal antibodies called AChR antibodies in your blood. These are autoantibodies – antibodies that mistakenly attack your own body. 

To understand what these antibodies do, you need to know how muscles normally work. When you want to move a muscle, your brain sends a signal down a nerve. At the end of the nerve, a chemical messenger called acetylcholine is released. 

Acetylcholine travels across a tiny gap to the muscle and docks onto special receivers called acetylcholine receptors. When acetylcholine attaches to these receptors, it triggers the muscle to contract. 

AChR antibodies interfere with this process in three ways. They can destroy the receptors, block them so acetylcholine can’t attach, or make them disappear from the muscle surface. Whichever way they work, the result is the same – muscles don’t receive proper signals and become weak. 

Most commonly, doctors test for binding antibodies which attach to the receptors. Sometimes if this test is negative but myasthenia gravis is still strongly suspected, other types of antibodies may be tested. 

If you have AChR antibodies in your blood and symptoms of myasthenia gravis, you very likely have this condition. These antibodies are not normally present in healthy people. 

The higher the antibody level, the more likely you are to have myasthenia gravis. However, antibody levels don’t directly reflect how severe your symptoms are. Some people with high levels have mild symptoms, while others with lower levels have more severe disease. 

Very rarely, very low levels of AChR antibodies may be found in people who never develop myasthenia gravis. 

A negative result doesn’t completely rule out myasthenia gravis. About 10–15% of people with generalised myasthenia gravis (affecting multiple muscle groups) test negative for AChR antibodies. 

Up to 50% of people with ocular myasthenia gravis (affecting only eye muscles) test negative. 

If your test is negative but your doctor still suspects myasthenia gravis, they may request other antibody tests such as anti-MuSK antibodies. 

AChR antibodies can occasionally appear in other conditions: 

• Thymomas (thymus gland tumours) 
• Small cell lung cancer 
• Autoimmune liver disease 
• Lambert-Eaton syndrome (a different neuromuscular condition) 
• Treatment with certain drugs like penicillamine 

If your test is positive 

Your doctor will usually: 

• Perform a clinical examination including specific nerve and muscle tests 
• May do an electromyography (EMG) test to check nerve-muscle communication 
• May give you a Tensilon test (edrophonium injection) to see if symptoms improve temporarily 
• Order a chest CT scan to check for thymus gland abnormalities 
• Refer you to a neurologist 

If myasthenia gravis is confirmed 

Treatment may include: 

• Acetylcholinesterase inhibitors (like pyridostigmine) – helps acetylcholine work longer 
• Immunosuppressants (like prednisolone, azathioprine) – reduce antibody production 
• Thymectomy (surgical removal of thymus gland) – may improve symptoms 
• Plasma exchange or immunoglobulin – for severe flare-ups 

With treatment, most people with myasthenia gravis can live a normal or near-normal life. However, it’s a chronic condition requiring ongoing management. 

Monitoring your condition 

Regular follow-up includes: 

• Clinical assessments of muscle strength 
• Repeat AChR antibody tests to monitor disease activity 
• Medication adjustments as needed 
• Watching for myasthenic crisis (severe breathing difficulty) 

Several factors can affect your test results: 

• Medications: drugs like succinylcholine (used in anaesthesia) can increase AChR antibodies 
• Penicillamine: this drug can cause antibody production 
• Disease stage: antibody levels may vary over time 

Tell your doctor about all medications you’re taking before the test. 

AChR antibody testing is often done alongside other tests: 

Other antibody tests: 

• Anti-MuSK antibodies – another cause of myasthenia gravis 
• Thyroid antibodies – thyroid disease often coexists 
• ANA (antinuclear antibodies) – other autoimmune conditions are more common 

Diagnostic tests: 

• Electromyography (EMG) – tests nerve-muscle communication 
• Tensilon test – temporary improvement with edrophonium injection 
• Repetitive nerve stimulation – shows muscle fatigue pattern 

Imaging: 

• Chest CT scan – to check for thymoma 
• MRI – if needed to investigate other causes 

Thyroid function: 

• Thyroid function tests – thyroid problems are common in myasthenia gravis 

Myasthenia gravis is an autoimmune condition where the immune system produces antibodies that interfere with nerve-muscle communication. It causes muscle weakness that gets worse with activity and improves with rest. 

The condition often starts with eye muscles (drooping eyelids, double vision) and can spread to other muscles. About 60–70% of people with myasthenia gravis have an enlarged or abnormal thymus gland. 

Myasthenia gravis only affects voluntary (skeletal) muscles – it doesn’t affect your heart muscle or the smooth muscles in your digestive system because these have different types of receptors. 

The condition is not contagious. However, pregnant women with myasthenia gravis can pass antibodies to their baby, causing temporary symptoms for the first few weeks after birth. 

Learn more about myasthenia gravis on NHS.uk, myaware, and Muscular Dystrophy UK