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Factor VII
8%
15/193
Factor VIII
49%
95/193
Factor IX
5%
10/193
Factor X
4%
8/193
Factor XII
28%
55/193
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This patient with an increased partial thromboplastin time as well as decreased bradykinin formation most likely has a defect in factor XII production or activity. The coagulation cascade can be divided into the extrinsic pathway and the intrinsic pathway. The intrinsic pathway consists of factors VIII, IX, XI, and XII, and this pathway can be tested using partial thromboplastin time (PTT). An isolated increase in PTT can be attributed to a defect in either the production or function of one of these factors. If prothrombin time is also elevated then altered function of common pathway members may be suspected. Notably, factor XII is the most upstream factor in the intrinsic pathway and is responsible for the activation of bradykinin. Therefore, decreased activation of bradykinin implicates defective factor XII function. Incorrect Answers: Answer 1: Factor VII is a member of the extrinsic coagulation pathway. A defect in this factor would present with an isolated increase in prothrombin time rather than an increase in partial thromboplastin time. Answers 2-3: Factors VIII and IX are members of the intrinsic pathway but they have no function in the activation of bradykinin. Therefore, defects in these factors would lead to an increased partial thromboplastin time but no effect on bradykinin. Answer 4: Factor X is a member of the common pathway so a defect in this factor would present with increases in both prothrombin time and partial thromboplastin time. Bullet Summary: Factor XII activates bradykinin as well as the intrinsic pathway of coagulation.
2.4
(17)
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