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July 13, 1940


JAMA. 1940;115(2):149-150. doi:10.1001/jama.1940.02810280061023

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To the Editor:—  From the literature and from our correspondence with many American investigators it seems that there have been several investigators who have had difficulty in understanding certain details in our method for the determination of prothrombin. As a number of methods have been suggested for this purpose, it might interest American investigators working on coagulation of human blood to hear about our experiences in this field.It is now generally agreed that the methods usually employed so far in the clinic for determination of the coagulation time and bleeding time are not accurate enough for examination of avitaminosis K and that the prothrombin has to be determined, i. e. that primarily the plasma has to be obtained without any admixture of tissue extract, and then the prothrombin in this plasma is determined by examining its coagulation on addition of tissue extract. Methods that do not follow this principle

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