Acetylcholine receptor antibody assay kit: establishment of controls in normals and non-myasthenics and evaluation of sera from patients with thyroid disease.

Immunoprecipitation assays for antibodies to the nicotinic acetylcholine receptor are a specific test for the diagnosis of myasthenia gravis. However, testing has largely been confined to reference laboratories because the preparation of the reagents is laborious, making it less accessible to practising clinicians locally. We recently acquired a test kit produced by RSR Ltd (Avenue Park, Pentwyn, Cardiff) which makes testing of serum samples practicable in smaller centres. We describe our experience in establishing normal and control values in 30 separate samples. We also assayed the sera of ten patients with thyroid disease, some of whom had ophthalmopathy and/or weakness due to periodic paralysis, and none of these tested positive. Three additional patients with thyroid disease and concurrent myasthenia gravis were also inadvertently included in the latter assay and two had high titres and one had equivocal titres. The assay is now run regularly every quarter of the year.