Homogeneous enzyme immunoassay for theophylline with a centrifugal analyzer.

A rapid homogeneous enzyme immunoassay for theophylline has been adapted to a centrifugal analyzer. The sample volume used was 10 microliter and sera from as many as 28 patients could be measured in 180 seconds. The assay temperature was 30 degrees and the absorbance rates were measured at 340 nm. Within-run and run-to-run precision showed a coefficient of variation of less than 2.6 and 7.5 percent, respectively, for theophylline concentrations of 2.5 to 40 mg per liter. The method was linear to 50 mg per liter and the analytical recovery was quantitative. A comparison between high pressure liquid chromatography (X) and the centrifugal analyzer enzyme immunoassay method (Y) for 51 patient samples revealed a correlation coefficient of 0.976 with a regression line of Y = 1.07 X -1.05 mg per liter. Reagent costs were reduced three-fold by adapting the enzyme immunoassay procedure from a semi-automatic spectrophotometer to a centrifugal analyzer. An absorbance rate for each theophylline sample was obtained by a multipoint kinetic rate computer program by the centrifugal analyzer. Severe hemolysis and lipemia interfered in this assay.