Correlation between Seralyzer reflectance photometer theophylline assay and an Emit assay

Recently a method for theophylline assay on the Ames Seralyzer was introduced. We compared the interday variability of this method to the established interday variability of an enzyme multiplied immunoassay (Emit) technique used in the service laboratory of a hospital. Control sera and calibrator prepared to known concentrations (10, 15, and 25 micrograms/mL) were assayed singly daily for ten days with the Seralyzer machine. Assays were done singly to simulate the in-office use of the machine. Their respective coefficients of variations (CVs) were 6.96%, 5.50%, and 5.23%, which compared favorably with the established CVs for the Emit of 6.7%, 5.8%, and 6.1% respectively at comparable test concentrations. Two hundred and fifty-one sera were assayed in parallel on both machines in eight batches. Linear regression analysis of these data showed a slope of 0.995, intercept of 0.468, and a correlation coefficient of 0.945. These data suggest that the Seralyzer values compared favorably with the Emit values.