Performance and in-house validation of a bioassay for the determination of beta1-autoantibodies found in patients with cardiomyopathy

BACKGROUND: Autoantibodies specific for the adrenergic beta1-receptor were identified to be an essential factor for the pathogenesis of dilated cardiomyopathy. For the detection of these autoantibodies, a bioassay was developed and has been used, measuring the positive chronotropic effect on spontaneously beating neonatal rat cardiomyocytes. In order to use this bioassay as an analytical tool to monitor the effectiveness of autoantibody neutralizing therapy in a regulated field, there is a need to assess its analytical performance and validate it according to current guidelines. METHODS: Using standard autoantibody samples, the increased beat rate compared to the basal rate [delta beats/min] was recorded when investigating guideline required assay performance parameters. RESULTS: The analytical specificity and sensitivity of the bioassay was demonstrated. The limit of detection and positivity cut-off level were determined to be 3.56 and 7.97 delta beats/min, respectively. The coefficient of variation (CV) of all tested single values (four technical replicates each) was ≤15.2%. The CV of precision within each measuring series did not exceed 20%. Furthermore, the sample stability under a variety of different storage conditions was assessed, as well as the robustness of the cardiomyocyte preparations, which were both given. CONCLUSION: This bioassay fulfilled guideline determined quality requirements and proved to be appropriate for its application in clinical trials.