Standardization of Methods for Measuring Plasminogen Activator Inhibitor Activity in Human Plasma

We have standardized the measurement of plasminogen activator inhibitor type 1 (PAl-i) activity in plasma. One-chain tissue-type plasminogen activator (t-PA; EC 3.4.21.31; final activity, 5 mt.units/mL) was incubated with plasma (final dilutions 1:4 to 1:40) in phosphate buffer (pH 7.4, ionic strength = 0.15) for 15 miri at37 “C, followed by acidification and measurement of residual t-PA activity by art amidolytic method. The PAl-i activity assay was 98 % specific for PAl-i activity in samples from both pregnancy and nonpregnancy, and varied linearly with added plasma volume when the percent inhibition of t-PA was between 8 % and 50%. For the standardized method, analytical recovery was 93 ± 5%, the detection limit was 1.6 arbitrary units per milliliter (1 arb. unit of PAl-i activity = inhibition of 1 mt.unit of t-PA activity), and total imprecision was 10.2 (SD 0.7) arb. units/mL (CV = 7%