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 hoursafter 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?

Question

Quizplus · Accepted Answer

The Answer is C
EXPLANATION: Factor XIII is also known as fibrinstabilizing 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-e-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 of factor XIII deficiency is made with a clot solubility screening test and confirmation was accomplished by demonstrating the absence of factor XIII by latex agglutination.

You Are Tending to a 5-Year-Old Boy with a Suspected