RICHARD N. PALMER, M.D.; CRAIG M. KESSLER, M.D.; HARVEY R. GRALNICK, M.D.
To the editor: The prothrombin time is the commonest test used to monitor oral anticoagulant therapy. In examining the prothrombin times of patients on oral anticoagulants and normal subjects, we have found a time-dependent shortening of the test when whole blood is kept in borosilicate (or glass) or in commercial siliconized borosilicate tubes, both at 4 °C, and to a lesser degree at 23 °C. This shortening of the prothrombin time is minimal when polypropylene tubes are used.
The prothrombin times for blood collected in borosilicate tubes are given in Figure 1. Almost identical results were found with commercial siliconized
PALMER RN, KESSLER CM, GRALNICK HR. Misinterpretation of Prothrombin Time in Warfarin Anticoagulation. Ann Intern Med. ;95:393–394. doi: 10.7326/0003-4819-95-3-393_2
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Published: Ann Intern Med. 1981;95(3):393-394.
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