Acetylcholine Receptor (AChR) Antibody

Function

The Acetylcholine Receptor (AChR) antibody test is a blood assay used to identify autoantibodies that interfere with the transmission of nerve impulses to muscles. In a healthy neuromuscular junction, acetylcholine is released from nerve endings and binds to AChR on the muscle surface, triggering contraction. These autoantibodies block, alter, or destroy these receptors, leading to muscle weakness.

Why it is Ordered

This test is the primary diagnostic tool for Myasthenia Gravis (MG). It is ordered for patients exhibiting symptoms such as:

• Ptosis: Drooping of one or both eyelids.
• Diplopia: Double vision.
• Bulbar Symptoms: Difficulty swallowing, impaired speech, or chewing fatigue.
• Proximal Muscle Weakness: Difficulty climbing stairs or lifting arms, which typically worsens with activity and improves with rest.

Associated Conditions

• Generalized Myasthenia Gravis: Approximately 85% of patients with generalized MG test positive for these antibodies.
• Ocular Myasthenia: About 50% of patients whose symptoms are restricted to the eyes will have positive AChR antibodies.
• Thymoma: There is a strong association between AChR antibodies and tumors of the thymus gland. High titers in an older patient often prompt chest imaging (CT/MRI).
• Lambert-Eaton Myasthenic Syndrome (LEMS): Though distinct (usually involving calcium channel antibodies), AChR may be checked during the differential diagnosis of neuromuscular junction disorders.