HOMOGENEOUS IMMUNOFLUOROMETRIC ASSAYS OF ALPHA-FETOPROTEIN WITH MACROPOROUS, MONOSIZED PARTICLES AND FLOW-CYTOMETRY

We evaluated two homogeneous immunofluorometric assays (IFMAs) of alph a-fetoprotein (AFP) based on new macroporous acrylate particles combin ed with flow cytometry. The standard IFMA, requiring 1 h of incubation , provided a working range from 1.8 to >900 kIU/L (CV < 10%) and a det ection limit of 0.6 kIU/L. Use of overnight incubation and a lower par ticle concentration extended the working range by 1 decade in the lowe r end. Analytical recoveries for the standard IFMA varied between 97% and 108%. The slope and y-intercept of the regression line correlating measurements by the standard IFMA and a routine immunoradiometric ass ay were not significantly different from 1 and 0, respectively (P >0.5 ), and the correlation coefficient was 0.996. High precision and warni ng of spuriously high measurements were obtained by including in each sample separate particle types for detecting instrument instability an d measuring nonspecific binding only.