Determination of alpha 1-antitrypsin in fecal extracts by enzyme immunoassay.

An enzyme immunoassay (EIA) has been developed for the determination of alpha 1-antitrypsin (AT). The assay can measure AT in fecal extracts (0.2 g wet feces/ml) from all healthy individuals. Purified human AT was coupled to peroxidase by means of a heterobifunctional reagent and the conjugate was used as a labeled antigen in competitive immunoassays. Concentrations of AT in feces from healthy individuals were less than 0.55 mg/g wet weight or less than 2.2 mg/g dry weight. CV for the physiological day-to-day variance varied between 9 and 140%. After incubation for 48 h at 37 degrees C, the average recovery rates for AT were 78% in ileostomy fluids, 88% in fecal extracts and 92% in feces. Results obtained with EIA correlated well with those obtained with a commercial radial immunodiffusion assay (r = 0.95).