Evaluation of the Hybritech Photon Analyzer and of an improved procedure for choriogonadotropin in serum.

We evaluated the Hybritech Photon Analyzer for its applicability to enzyme immunoassays. This instrument measures absorbances only at 405, 450, and 490 nm. Photometric linearity was good at all three wavelengths. However, the true absorbance range at these wavelengths was 0-1.6 A instead of 0-2.0 A as specified by the manufacturer. We also evaluated the Hybritech "Tandem-E" method for quantifying choriogonadotropin (hCG) in serum. A modification of the recommended procedure improved the precision of the assay. The detection limit of the modified procedure, 1 int. unit/L, permits reliable assays of hCG at concentrations near the upper limit of normal (3 int. units/L). Results by both procedures varied linearly with hCG concentrations up to 250 int. units/L. The Photon Analyzer eliminates the need for manual calculations. Quantitative results agree within +/- 1% with those measured in the "Stasar III" spectrophotometer.