Our May, 2021 Quick Question was a historical factor name challenge, “What is the more common name for Flaujeac factor?” The question drew 24 responses. We answered:
- Hageman factor: 21% 
- Fletcher factor: 4% 
- Fitzgerald factor: 58% X
- Stuart factor: 13% 
- Fibrinogen: 4% 
High molecular weight kininogen [HMWK] was given the name Fitzgerald factor in 1975 when its absence was first detected in the Fitzgerald family of Detroit. HMWK deficiency is an autosomal recessive trait that prolongs the PTT but has no bleeding consequences. Fitzgerald had a 50% HMWK level, however the Washington and Williams families were found to have less than 1%, and the Flaujeac family [in France], 9%. HMWK is sometimes called the Fitzgerald-Williams-Flaujeac factor.
Hageman factor is factor XII, whose common autosomal recessive absence was first detected in John Hageman in 1962. There appears to be no bleeding consequence associated with factor XII deficiency, and in fact, Mr. Hageman later died of a pulmonary embolus.
Fletcher factor is prekallikrein [PK], an autosomal recessive deficiency that was detected with an unexpected prolonged PTT in five members of the Fletcher family, all negative for a bleeding tendency. Specialty reference laboratories offer factor assays for HMWK and PK, however PK deficiency may also be detected using a PTT modified with a prolonged patient plasma-reagent incubation, whereupon the PTT reverts to within the reference interval. Recent studies indicate that PK directly activates facotr IX and could be a target for a new direct anticoagulant with little concern for bleeding.
Stuart factor, or Stuart-Prower factor is factor X  whose absence was first described in Mr. Stuart and Ms. Prower, and also the Girolami family in 1970. The first described factor X deficient families were all from a small, isolated valley in northern Italy called the Friuli region so some named the factor Factor X-Friuli. There are many factor X variants, mostly autosomal recessive, and factor X deficiency is associated with anatomic bleeding.
Fibrinogen was once called factor I and was first described in 1920. Fibrinogen deficiency, called afibrinogenemia, is autosomal recessive and is associated with severe bleeding.
This information was taken from Triplett DA. Chapter 3: Congenital coagulation factor deficiencies [excluding abnormalities of factor VIII]. In Triplett DA. Laboratory Evaluation of Coagulation, ASCP Press, 1982. The late Dr. Triplett was a hemostasis giant whom we all miss. In May of 2007, as George developed this blog with the managers of Precision BioLogic, Inc, friend and colleague Stephen Duff proposed the name “Fritsma Factor,” noting the alliteration of Fitzgerald, Fletcher, Flaujeac, and “factor.” While the name first struck George as a little too self-referent, Steve’s argument prevailed.