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June 2, 1956


JAMA. 1956;161(5):475. doi:10.1001/jama.1956.02970050077023

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To the Editor:—  The Norwegian correspondent writing in the Foreign Letters section (J. A. M. A.160:583 [Feb. 18] 1956) has misinterpreted three important points regarding my article on anticoagulant therapy (Nord. med.54:1733 [Nov. 17] 1955). Firstly, he states: "In order to achieve a specific quantitative test for both prothrombin and proconvertin, he [Owren] has combined the Russell viper venom method for determining prothrombin with use of proconvertin-free ox plasma (or congenitally proconvertin-free human plasma) as a reagent." This statement is incorrect. The prothrombin-proconvertin method was developed as an entirely new method to measure the combined effect of prothrombin and proconvertin in a single test. It is specific for neither factor and bears no direct relationship to either the viper venom method for prothrombin or the specific proconvertin method. Indeed, in describing the viper venom method for prothrombin (J. Lab. & Clin. Med. 46:89 [July] 1955), the

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