Our March, 2021 Quick Question was a case study that netted 49 votes. A 2 YO experiences frequent joint bleeds. PT : 22s; PTT : 29s; fibrinogen 280 mg/dL. What do you do next?
- Assay factors VIII, IX, and XI. 10% 
- Assay factors II, V, and X, 14% 
- Assay factor VII, 70% [34, correct]
- Assay factor XII, PK , and HMWK 6% 
Autosomal factor VII  deficiency is the only single factor deficiency that prolongs only the PT. A review of the coagulation cascade illustrates that the PT is prolonged by deficiencies of VII, X, V, prothrombin, and fibrinogen if the fibrinogen level is below 100 mg/dL. The PTT is prolonged by any coagulation factor deficiency except for FVII. The prevalence of FVII deficiency is uncommon at 1 in 500,000, and although heterozygotes are asymptomatic, they may occasionally be detected by the prolonged PT.
Escobar MA. Less Common Congenital Disorders of Thrombosis. In Kitchens CS, et al. Consultative Hemostasis and Thrombosis Edition 4, 2019.