A control chart method for evaluating hemagglutination reagent used in Chagas' disease diagnosis.

Laboratories that develop or produce their own antigen reagents for serodiagnostic purposes need a practical and reliable quality control method for evaluating the successive batches of standardized reagent, so as to ensure the reproducibility of test results. Although a large number of statistical models are available for quality control analysis of therapeutic agents or clinical laboratory equipment and procedures (1, 2)) very few have been described for the evaluation of serologic reagents. This is probably because such reagents constitute a special category of biological products that measure intricate antibody activities in the sera of infected patients. The measurable output index, known as a titer, results from complex interactions between multiple epi-