Abstract
With increasing use of tests of the prothrombin time as an aid in the diagnosis of diseases of the liver and as a guide in vitamin K and dicoumarol therapy, it is imperative that the determination be accurate. | Lack of experience with the test results in erroneous reports. Precise technique can be achieved only by practice and by strict attention to the details of the test. The end point agreed upon must be unmistakable and constant. However, the main factor in the test is the use of a uniform standardized stable thromboplastin.