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To the Editor:—
It is easy to comprehend Dr. Vigran's difficulty in understanding my comments (JAMA176:1127 [July 1] 1961) concerning his paper (JAMA176:188 [April 22] 1961) because he has uncritically accepted the claim that the Thrombotest is sensitive to Factor IX. I have found that the Thrombotest is completely normal when tested on the plasma from a patient with severe hemophilia B, whose blood contains only a trace of Factor IX. Neither the Thrombotest nor my test is sensitive to Factor IX, but my test, however, is exceedingly sensitive to Factor VII, the factor which is primarily reduced by avitaminosis K, whether induced by diet or by antivitamin K drugs such as bishydroxycoumarin (Dicumarol).By a slight modification, namely, adding one-tenth volume of aged serum, which is rich in Factors VII and X to the plasma, the one-stage prothrombin time is made specific for free prothrombin
Quick AJ. Quick's One-Stage Prothrombin Time-Reply. JAMA. 1961;178(11):1119. doi:10.1001/jama.1961.03040500060018