1. Overview
Factor V is a cofactor glycoprotein that plays a crucial role in both the coagulation and anticoagulation pathways. It is synthesized in the liver and released into the bloodstream in an inactive form. The functional role of it depends on its modification by either activated Factor X or activated Protein C (aPC).
Activated Factor V (FVa) serves as an essential cofactor in the conversion of prothrombin to thrombin, a key step in clot formation. In contrast, inactive (zymogen) Factor V works alongside protein S to support activated Protein C–mediated inhibition of Factor VIIIa, thereby regulating clot formation.
This Deficiency is a very rare bleeding disorder known as Owren disease or parahemophilia and may occur in congenital or acquired forms.
2. Symptoms
Clinical manifestations related to Factor V abnormalities depend on whether the defect leads to bleeding or thrombosis. Deficiency commonly presents with bleeding symptoms, which may include easy bruising, petechiae, epistaxis, hematuria, menorrhagia, hematemesis, melena, hemarthrosis, hemoptysis, and prolonged bleeding following surgery or trauma.
In contrast, elevated plasma levels or abnormal activation of this may increase the risk of thrombotic events. Thus, symptoms vary widely based on the functional imbalance within the coagulation cascade.
3. Causes
Factor V abnormalities may be congenital or acquired. Congenital deficiency is inherited and rare, while acquired forms may develop due to antibodies or other pathological conditions affecting coagulation.
The dual regulatory role of this explains why defects can result in either excessive bleeding or increased clot formation. The balance between procoagulant and anticoagulant pathways is essential for maintaining normal hemostasis, and disruption of this balance leads to clinical disease.
4. Risk Factors
Risk factors associated with Factor V disorders include a personal or family history of bleeding or thrombotic events, abnormal coagulation profiles, and symptoms suggestive of excessive bleeding. High plasma levels of Factor V increase prothrombinase activity and subsequently raise the risk of thrombosis.
Deficiency severity is classified based on Factor V activity levels: mild deficiency with activity greater than 10%, moderate deficiency with activity between 1–10%, and severe deficiency with activity below 1%.
Certain clinical conditions, such as venous thromboembolism, autoimmune disorders, malignancies, and inherited mutations (including Factor V Leiden carriers), may influence Factor V expression and activity.
5. Prevention and Clinical Management
Management of Factor V disorders relies on accurate diagnosis, laboratory testing, and appropriate clinical correlation. Indications for testing include unexplained bleeding symptoms, prolonged bleeding after surgery or trauma, abnormal bruising, suspected activated protein C resistance, and evaluation for Factor V Leiden mutation when indicated.
Patients are advised to discontinue anticoagulant therapy, such as warfarin, at least two weeks before testing and to avoid direct Xa inhibitors, heparin, and thrombin inhibitors for at least three days before sample collection. Blood samples should not be drawn from heparinized catheters.
Citrate plasma is used for coagulation assays, while immunohistochemistry (IHC) is performed on formalin-fixed paraffin-embedded tissue to detect Factor V antigen. Endothelium serves as a positive internal control in IHC analysis, and positivity is defined by moderate to strong coarse or granular cytoplasmic staining.
Laboratory evaluation includes assays such as activated protein C resistance testing, PCR-based molecular methods, restriction fragment length polymorphism analysis, real-time PCR, DNA sequencing, and ELISA.
Diagnostic utility extends to distinguishing congenital from acquired deficiencies, assessing thrombosis risk, guiding anticoagulation decisions, screening first-degree relatives, and supporting management decisions in high-risk scenarios such as surgery, pregnancy, and estrogen exposure. Limitations include variability in expression and the inability of certain tests to detect all genetic or acquired abnormalities.
