[Detection of blood coagulation inhibitors using a modified Lossing-Kasper test]

Inhibitors, particularly against factor VIII or IX, are generally determined by the Bethesda method, which is time-consuming and of moderate sensitivity. Since the residual factor VIII/IX activity in a mixture of patient's and normal plasma is only measured after incubation, it provides no information on the kinetics of inactivation. Whereas a protracted inhibitory activity is observed in haemophiliacs after replacement therapy (isoantibodies) as well as in acquired haemophilia (autoantibodies), immediate inhibition is characteristic of antibodies directed against phospholipids. For clinical and therapeutic reasons it would be necessary to discriminate between these two kinds of inhibitor. Our modification of the Lossing & Kasper screening test eliminates these disadvantages: it is highly sensitive (patient's and normal plasma are mixed at a 4:1 ratio), easy to perform (aPTT system), and comparison of the tests with plasmas mixed before and after incubation makes it possible to distinguish between fast and slow inhibitors. The highly reproducible test is performed as follows: 0.4 ml of patient's plasma is added to tube 1 (T1), 0.4 ml of normal pooled plasma to tube 2 (T2) and a mixture of 4 parts patient's and 1 part normal plasma to tube 3(T3). After incubation (2 hrs, 37 degrees C) patient's and normal plasmas incubated separately are mixed at a 4:1 ratio (T1+2). aPTTs are performed with T1+2 and T3, using a chloroform brain extract diluted 1:400 and supplemented with kaolin 2 mg per ml of diluted chloroform brain extract. In the absence of an inhibitor aPTTs are in the region of 70 sec.(ABSTRACT TRUNCATED AT 250 WORDS)