Control of Vitamin K Therapy. Compensatory Mechanisms at Low Prothrombin Levels. ∗

The use of vitamin K to combat the lowered plasma prothrombin level in jaundiced bleeders 1 , 2 has created a demand for a simple clotting test. Quick 3 has suggested the use of whole blood as a test for thromboplastic activity; we propose to reverse the procedure, and use thromboplastin, in large amounts, to test the clotting power of whole blood. We also propose to show that deficiency in prothrombin can be compensated in part by changes in other factors.

The test. In a 3 cc tube is placed 0.1 cc thromboplastin. Blood, freshly drawn, is run into the tube to a 1.0 cc mark, then inverted once, and tilted gently every few seconds, and the clotting time observed. The test is repeated on a normal individual, and the unknown expressed in percentage of the normal.

For example, a patient's blood clotted in 60 seconds, a control in 30. Activity, therefore, was 50% of normal.

To prepare thromboplastin, extract 10 g ground brain or lung (ox or rabbit) 2 hours with 10 cc saline; strain, and preserve in ice box. Variable potency does not affect the clotting time ratio of unknown to control. If normal values exceed 60 seconds, the thromboplastin is rejected; if less than 25 seconds one should dilute the thromboplastin with saline.

Results. Table I shows results on 10 cases selected at random from our series. The prothrombin levels obtained by the 2-stage titration procedure developed in this laboratory 4 serve as a standard. It is seen that the values obtained with the new test usually agree within 15% with the true prothrombin levels, indicating that the new test is dependent in large part upon the prothrombin concentration.