The blood sampling and handling procedure for a recently developed BioImmunoAssay (BIA) kit method has been evaluated. It was observed that blood collection at acid pH (pH 6; Stabilyte(R) tubes) yielded higher t-PA activity values (median 317 mIU/ml; 95% CI: 127-424) than collection in citrate (median 89 mIU/ml; 95% CI: 6-135) (n = 25 healthy volunteers). The BIA results in citrated plasma are comparable to results with other methods: t-PA activity in normal euglobulin fractions recorded with a chromogenic assay (median 5 mIU/ml; 95% CI: 5-36) or on the fibrin plate method (median 195 mIU/ml; 95% CI: 85-405). Further acid treatment of Stabilyte plasma yielded again higher values in the BIA (median 386 mIU/ml; 95% CI: 225-518); the increase in t-PA activity due to additional acid treatment correlated with the plasminogen activator inhibitor (PAI) activity in the plasma. Comparison between the t-PA activity obtained with the BIA method and our own in-house chromogenic assay method using in both cases acid treated plasma showed a strong correlation (r = 0.962, P < 0.0001, n = 25). We concluded that measurement of t-PA activity with the BIA can reliably be done provided blood is collected in acid milieu and plasma is subjected to additional acid treatment to inactivate PAI.
