Acetylcholine receptor (AChR) antibody Test

AChR test is recommended as the first-order test for patients who present symptoms of myasthenia gravis. It is also performed to monitor the response of myasthenia gravis treatment using immunosuppressants. 

The antibodies for myasthenia gravis are present in almost 85% of the patients who suffer from the disease. There are three types of AChR antibodies: AChR binding antibodies, AChR blocking antibodies and AChR modulating antibodies. AChR blocking antibodies are mainly useful in testing the response to immunosuppressant therapy. The symptoms of myasthenia gravis range from the weakness of respiratory muscles to muscular weakness in the entire body.

Doctors advise this test when they observe the following symptoms in a patient:

• Drooping of one or both eyelids (ptosis)
• Blurred vision or double vision
• Shortness of breath
• Abnormal speech
• Changes in facial expression
• Difficulty in chewing and swallowing (Read more: Difficulty swallowing causes)
• Unstable gait due to muscular weakness in arms and legs

Weakness tends to be worse towards the end of the day and after exercise in myasthenia gravis patients. When the disease affects a patient’s ability to breathe or swallow, the condition becomes life-threatening.

You don’t need to do any special preparations for this test. Before conducting the test, your doctor will explain the purpose and procedure of the test to you.

The test involves the collection of a blood sample (7 mL) from a vein in the arm using venepuncture. A technician will clean the site of puncture with povidone-iodine and withdraw the required amount of blood. The blood sample will be labelled and sent to the laboratory for further analysis.

Normal results:

A negative result, which indicates the absence or a blood concentration of less than 0.02 nmol/L of AChR antibodies, is considered as the normal result.

Abnormal results:

Higher than 0.02 nmol/L of AChR antibodies in the blood sample is considered abnormal. Depending on the neurological symptoms seen in the patient, the doctor may also suggest other serological tests, which include testing specifically for the AChR blocking antibody, AChR modulating antibody and the striational antibodies. Abnormally high values of AChR antibodies suggest the presence of myasthenia gravis. Some important findings related to the AChR antibody test are as follows:

• Around 90% of patients suffering from generalised myasthenia gravis show abnormally high concentration of AChR antibodies, and 70% of the patients suffering from ocular myasthenia gravis show abnormal results. Around 80% of patients who have remission of this autoimmune condition also show a high concentration of the antibody
• Some immunosuppressant drugs may decrease the AChR antibody titre
• Also, in the earlier stages of myasthenia gravis, the frequency of detection of antibodies is less; whereas, in patients with congenital myasthenia gravis, the antibodies are nil
• Patients who have only eye symptoms also show low titre values of AChR antibodies than those who have generalised myasthenia gravis. In ocular myasthenia gravis, some ancillary tests are often suggested to confirm the presence of the disease
• Sometimes, false-positive results are obtained in patients with Lambert–Eaton myasthenic syndrome or autoimmune liver disease. Nevertheless, patients who have received anaesthesia or muscle relaxant up to 48 hours before the test may also show false-positive results. Patients with amyotrophic lateral sclerosis also show false-positive results

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.