Determination of Plasminogen in Human Plasma by a Casein Method*

Summary A modification of the casein method for determination of plasminogen in plasma has been devised. 1. Urokinase instead of streptokinase was used for activation of plasminogen in order to eliminate the effect of any antistreptokinase antibodies in the plasma. 2. A purified and stable plasmin preparation according to Wallén was used for preparing reference curves. 3. The plasminogen activity of plasma was converted into arbitrary casein - olytic units (ACU) defined in such a way that 10 caseinolytic units gave an extinction of 0.300. 4. Removal of the plasmin inhibitors by acidification of plasma to pH 2.0 was found to be better than using euglobulin precipitation. 5. The plasma should be tested immediately after thawing and not allowed to stand after acidification for obtaining optimal conditions. 6. The method can be used for determination of plasminogen in plasma in patients treated with ssss-ACA and AMCA. 7. The error of the method was found to be small ssss0.4. The mean plasminogen level in a normal group of 72 was found to be 9.5 ssss 1.7 ACU/ml plasma. No variation with sex and age was found. The method proved clinically useful. During the latter half of pregnancy the plasminogen level was found to be clearly elevated. In patients with liver cirrhosis the plasminogen level was low. It was a sensitive method for following the plasminogen content during streptokinase treatment.