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Chapter 51: Hemostasis: Blood Coagulation

You are examining a 9-year-old boy who is brought in by his parents for unexplained bleeding problems from birth. He experiences easy bruising, bleeding from the gums, and frequent epitaxis. His parents were first cousins, but they showed no bleeding problems. Hemostatic analysis of the boy's blood showed dramatically prolonged plasma prothrombin clotting time. Given the limited data in this case, a defect/deficiency in which of the following is most likely in this patient?

A. factor VIII

B. factor XI

C. factor XIII

D. fibrinogen

E. high-molecular-weight kininogen, HMWK

Answer D: Defects associated with factors of the pathways of blood coagulation can also be assessed with specific assays. The prothrombin time (PT) is an assay designed to screen for defects in fibrinogen, prothrombin, and factors V, VII, and X and thus measures activities of the extrinsic pathway of coagulation. When any of these factors is deficient then the PT is prolonged. A normal PT is 11.0 to 12.5 seconds. A PT greater than 20 seconds is indicative of coagulation deficit.

You are tending to a 5-year-old boy with a suspected case of congenital deficiency in coagulation. He had bled from the umbilical and circumcision sites during his first week of life. He experiences frequent ecchymoses and hematomas within 12 to 24 hours after trauma. His parents are first cousins, but there is no family history of bleeding disorders. A bleeding disorder workup was initiated and the results indicated that PT, PTT, fibrinogen, platelet aggregation studies, and von Willebrand factor were normal. The patient's plasma was incubated with thrombin and Ca2+ and the resultant clot dissolved in the presence of urea. Given these findings, which of the following is most likely defective/deficient in this patient?

A. factor VII

B. factor VIII

C. factor XIII

D. tissue factor pathway inhibitor, TFPI

E. prothrombin

Answer C: Factor XIII is also known as fibrin-stabilizing factor or fibrinoligase. Factor XIII is converted to its active form (XIIIa) by thrombin in the presence of Ca2+. The reaction catalyzed by factor XIIIa is the formation of γ-glutamyl-ε-lysine bonds between fibrin monomers. Deficiency in factor XIII is characterized by delayed bleeding even though primary hemostasis is normal. Typical symptoms include neonatal bleeding from the umbilical cord, intracranial hemorrhage, soft tissue hematomas, recurrent spontaneous miscarriage, and abnormal wound healing. Umbilical cord bleeding after birth occurs in over 90% of afflicted individuals. Presumptive diagnosis ...

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