Acetylcholine Receptor Antibodies (AChR, Anti-ACh Antibodies)

Test Description

Acetylcholine (ACh) and the catecholamines (epinephrine and norepinephrine) are

the main neurotransmitters of the autonomic nervous system. In normal contraction

of the muscles, ACh is released from the terminal end of the nerve into the neuromuscular

junction. ACh then binds with receptor sites on the muscle membrane,

resulting in the opening of sodium channels. This allows sodium ions to enter and

depolarize the cell. This begins an action potential that passes along the entire

muscle fiber, resulting in muscle contraction.

Myasthenia gravis (MG) is an autoimmune disease that affects neuromuscular

transmission. In this disease, antibodies form that interfere with the binding of ACh

to the receptor sites on the muscle membrane. This prevents muscle contraction

from occurring. These antibodies are present in more than 85% of the patients with

MG. Thus, this test is used for diagnosis of MG and for monitoring the patient’s

response to immunosuppressive therapy for the disease.

Normal Values

Negative or ≤0.03 nmol/L

Possible Meanings of Abnormal Values

Increased

Myasthenia gravis

Contributing Factors to Abnormal Values

        •     False-positive results may occur in patients with amyotrophic lateral sclerosis (ALS).

        •     Drugs that may decrease ACh receptor antibody titers: immunosuppressive drugs.

Interventions/Implications

Pretest

   • Explain to the patient the purpose of the test and the need for a blood sample to be drawn.

   • No fasting is required before the test.

   Procedure

    • A 7-mL blood sample is drawn in a red-top tube.

    • Gloves are worn throughout the procedure.

Post test

    • Apply pressure at venipuncture site. Apply dressing, periodically assessing for continued

bleeding.

    • Label the specimen and transport it to the laboratory.

    • Report abnormal findings to the primary care provider.

clinical alert 

         • Three types of acetylcholine receptor antibodies are available for testing. The

          most common is the ACh receptor binding antibody. If this test is negative, testing

         for the blocking antibody and the modulating antibody should be done.

         • The ACh receptor blocking antibody is especially useful in monitoring response

         to therapy.