Simple, sensitive method for measuring plasmin and plasminogen activity in plasma.

We describe a sensitive, simple, and rapid method for measuring plasmin and plasminogen in plasma, with fibrinogen as substrate. The assay can be done within 1 h. Plasma is diluted 20-fold with buffer and 0.1 ml (5 mul of original plasma) is incubated for 5 min at 37 degrees C, with or without 400 units of streptokinase. Then 2.0 ml of fibrinogen solution is added, the mixture again incubated (37 degrees C, 5 min), and the reaction stopped. The amount of tyrosine liberated from the fibrinogen is measured and is related to activity. This method is suitable for routine clinical work if the same batch of fibrinogen is used.