To validate the live cell-based assay (CBA) for testing of clustered acetylcholine receptor antibodies (AchR Ab) in serum in the diagnosis of myasthenia gravis (MG)

A large proportion of generalized MG patients have detectable AchR Ab or muscle-specific tyrosine kinase antibodies (MuSK Ab) by radioimmunoprecipitation (RIPA). A live CBA that involves expressing clustered AchR on the cell surface through the co-expression of intracellular anchoring protein rapsyn has demonstrated the ability to detect AchR Ab measured by RIPA, as well as clustered AchR Ab in 16% to 60% of MG patients that do not have measurable AchR Ab or MuSK Ab by RIPA.

100 serum samples, 50 positive for AchR Ab by RIPA and 50 healthy controls, were blinded and assayed three times on different days by clustered AchR live CBA. Additionally, a cohort of 45 samples from children 16 years old and younger that had previously tested AchR Ab RIPA negative or borderline was assayed.

One sample that was previously RIPA positive was omitted due to a processing error before blinding. 100% concurrence was observed with CBA results between the three blinded assays of 100 samples. Of the 49 RIPA positive, 48 tested CBA positive or low positive, and one was negative. All 50 healthy controls tested CBA negative. Of the 45 children samples that were tested, 7 were CBA positive. Follow-up of these 7 showed that 3 have ocular MG and 4 have generalized MG.

The clustered AchR live CBA is a highly sensitive and replicable assay. It has shown to improve diagnostic sensitivity of MG particularly in children and those with overall milder disease.