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July 25, 1980

Anticoagulant Therapy

Author Affiliations

Frenchay Hospital Bristol, England

JAMA. 1980;244(4):333. doi:10.1001/jama.1980.03310040017014

To the Editor.—  In the report of Szklo et al (242:1261, 1979) and the editorial (242:1291, 1979), the indications for a carefully controlled large multi-institutional, double-blind, randomized study of the long-term effects of anticoagulant therapy during the acute phase of myocardial infarction are discussed. One additional variable not mentioned is the level of anticoagulation. The therapeutic range of the prothrombin ratio used in the United Kingdom (British Comparative Ratio) is 2.0 to 4.0. For many years I have used the activated partial thromboplastin time (APTT) to control long-term warfarin therapy.1 Using a Coag-a-pet coagulometer, I have recently collected 1,109 paired prothrombin ratios and APTTs during long-term warfarin therapy. The normal untreated APTT mean value is 32±10 s (2 SD). Of 685 results from anticoagulated patients with a prothrombin ratio of 2.0 to 2.9, 33% (226) had APTT results of less than 42 s, while out of 424 results with a prothrombin