Test Background The most sensitive and specific test for myasthenia gravis is the presence of ACR. Myasthenia gravis is a neuromuscular disorder characterised by weakness and fatigability of skeletal muscles. The aetiology involves a numerical decrease in the number of available acetylcholine receptors at the neuromuscular junctions due to an antibody-mediated autoimmune attack. Not all patients who have myasthenia gravis have positive ACR titres. ACR antibodies are seen in 45 % to 65 % of patients with ocular myasthenia and in approximately 90 % of patients with generalised myasthenia gravis. The degree of ‘positivity’ for the test results does not correlate with the severity of disease.