Specificity of antigen assays of plasminogen activator inhibitor in plasma: Innotest PAI-1 immunoassay evaluated.

We evaluate a new commercial enzyme immunoassay (EIA) of plasminogen activator inhibitor-1 (PAI-1) in plasma, the Innotest PAI-1. Because we wanted to measure PAI-1 in blood samples, we developed a procedure for evaluating the specificity of the assay for different PAI-1 forms in their natural environment. All molecular forms were prepared from a plasma that contained only active PAI-1. The recovery of the different molecular forms of PAI-1, relative to active PAI-1 (100%), was 99% +/- 7% for PAI-1 complexed with recombinant tissue-type plasminogen activator (t-PA), 104% +/- 4% for PAI-1 complexed with melanoma t-PA, 94% +/- 11% for PAI-1 complexed with high-M(r) urokinase, and 113% +/- 3% for latent PAI-1. The parallelism between the calibration curve of the EIA and the serial dilutions of the different PAI-1 forms was considered acceptable for clinical purposes. In selected clinical plasma samples, the PAI-1 values obtained with the Innotest PAI-1 EIA correlated well with those of the TintElize PAI-1 EIA (r = 0.913, n = 106); the observed correlation of the Innotest measurements with PAI activity was r = 0.795 (n = 79). The Innotest PAI-1 antigen assay appears to detect all molecular forms of PAI-1 to a similar degree, and comes close to being the so-called grand total assay for detecting the total molecular concentration of PAI-1 in plasma.