Factor XI Deficiency
An inherited bleeding disorder caused by reduced factor XI (FXI) activity, resulting in impaired amplification of thrombin generation. It is characterised by a highly variable bleeding phenotype, with bleeding most commonly occurring after surgery, trauma, dental procedures, or at sites with high fibrinolytic activity. Unlike haemophilia A and B, the severity of bleeding correlates poorly with the measured FXI level.
Epidemiology
Factor XI deficiency is a rare inherited bleeding disorder, although it is substantially more common in certain populations. The estimated prevalence in the general population has been reported at approximately 1 in 10,000–20,000 individuals, while severe congenital deficiency is much rarer. The condition is particularly prevalent among individuals of Ashkenazi Jewish ancestry, in whom partial deficiency occurs in approximately 1 in 20 individuals. Both sexes are affected because the F11 gene is located on an autosome.
Clinical description
Factor XI deficiency has a highly variable clinical presentation. Many individuals have no spontaneous bleeding and only develop excessive bleeding following surgery, trauma, dental extraction, or other haemostatic challenges. Bleeding is particularly associated with procedures involving tissues with high fibrinolytic activity, including the oral cavity, nose and throat, and genitourinary tract.
Common manifestations include excessive bleeding following surgery or dental procedures, epistaxis, easy bruising, menorrhagia, postpartum haemorrhage, and soft-tissue bleeding. Spontaneous joint and muscle bleeding, which are characteristic of severe haemophilia A or B, are uncommon.
The bleeding phenotype varies considerably between individuals with similar FXI levels. Individuals with severe deficiency may have relatively mild bleeding, whereas some individuals with partial deficiency may experience significant bleeding. A personal history of bleeding, particularly previous surgical or obstetric bleeding, is therefore often more informative for predicting future bleeding risk than the FXI level alone.
Etiology
Congenital factor XI deficiency is caused by pathogenic variants in the F11 gene, which encodes coagulation factor XI. Factor XI participates in the intrinsic coagulation pathway and contributes to amplification of thrombin generation following its activation.
The disorder is most commonly inherited in an autosomal recessive manner, particularly in individuals with severe deficiency. However, some heterozygous individuals may have reduced FXI levels and clinically significant bleeding, and autosomal dominant inheritance has also been reported. The relationship between genotype, FXI activity, and bleeding phenotype is complex and incompletely understood.
Acquired factor XI deficiency due to an inhibitor is rare and should be distinguished from congenital disease, particularly when a patient develops a new isolated prolonged aPTT and has no previous bleeding history. Acquired FXI inhibitors have been reported in association with autoimmune disease and other conditions.
Diagnostic methods
Diagnosis is based on demonstration of reduced FXI activity, usually in the context of an isolated prolonged activated partial thromboplastin time (aPTT).
Typical laboratory findings include:
– Prolonged aPTT with a normal PT
– Reduced FXI coagulant activity (FXI:C)
– Correction of the aPTT on mixing with normal plasma, supporting a factor deficiency rather than an inhibitor
– Normal fibrinogen and platelet count
FXI activity is generally markedly reduced in severe deficiency, often below 15–20 IU/dL, while partial deficiency may produce intermediate levels. However, the precise reference range varies between laboratories. Importantly, FXI activity should not be used alone to predict bleeding risk, because the correlation between factor level and clinical phenotype is poor.
The diagnosis should therefore incorporate the personal bleeding history and, where appropriate, family history and the nature of previous haemostatic challenges.
Molecular genetic testing of F11 can confirm the underlying genetic cause and is particularly useful for family studies or unusual phenotypes, but it is not required to establish the biochemical diagnosis in most patients.
Differential diagnosis
Differential diagnoses include:
– Haemophilia A or B
– von Willebrand disease, particularly type 2N or other forms associated with reduced FVIII
– Other intrinsic pathway factor deficiencies, particularly factor XII, prekallikrein, and high-molecular-weight kininogen deficiencies
– Lupus anticoagulant or other coagulation inhibitors
– Acquired haemophilia or acquired factor XI inhibitor
– Anticoagulant drug effects
– Combined or multiple coagulation factor deficiencies
Factor XII, prekallikrein and high-molecular-weight kininogen deficiencies can produce a prolonged aPTT without a clinically significant bleeding tendency and should not be mistaken for FXI deficiency. A mixing study and specific factor assays are therefore important when investigating an isolated prolonged aPTT.
Genetic counseling
Genetic counselling should be considered because congenital factor XI deficiency is an inherited disorder. Severe deficiency is usually associated with autosomal recessive inheritance, meaning that individuals with biallelic pathogenic variants are affected, while heterozygous carriers may have partial deficiency and, in some cases, clinically relevant bleeding.
The inheritance pattern can be complex in some families, and heterozygous individuals may show variable expression. Molecular testing can therefore be useful for cascade testing and reproductive counselling in families with an identified F11 pathogenic variant.
Congenital factor XI deficiency
Prevalence
1 / 10,000–20,000
Management and treatment
Management is individualised according to the patient’s bleeding history, FXI level, type and location of the procedure, and anticipated haemostatic challenge. Because bleeding risk is difficult to predict from FXI activity alone, previous bleeding during surgery or other haemostatic challenges is an important consideration.
Treatment options include:
– Antifibrinolytic agents, particularly tranexamic acid, which are highly useful for mucosal bleeding and dental, ENT, and other procedures involving tissues with high fibrinolytic activity. Tranexamic acid alone is sufficient for many patients and procedures.
– Fresh frozen plasma to increase FXI levels when replacement therapy is required, particularly where FXI concentrate is unavailable.
– FXI concentrate may be considered for selected patients with severe deficiency undergoing major procedures or experiencing significant bleeding, but it is associated with a recognised risk of thrombotic complications and should therefore be used cautiously under specialist supervision.
– Recombinant activated factor VII (rFVIIa) may be used as a bypassing agent, particularly in patients with FXI inhibitors or when FXI replacement is unsuitable, although thrombotic risk must also be considered.
– Hormonal therapy and/or tranexamic acid may be used for heavy menstrual bleeding.
– Desmopressin (DDAVP) has been reported to produce variable increases in FXI but does not have a sufficiently reliable effect to be considered routine treatment for FXI deficiency.
Perioperative and obstetric management should be planned in advance with a haemostasis specialist. Previous bleeding history is an important predictor of perioperative or obstetric bleeding, and antifibrinolytic therapy is frequently effective. Replacement therapy is reserved for patients in whom the clinical phenotype and/or procedure indicates a higher bleeding risk.
Prognosis
Prognosis is generally good, particularly because spontaneous severe bleeding is uncommon. Most individuals have a mild or moderate bleeding phenotype and remain well outside periods of haemostatic challenge.
The principal clinical risk is unexpected or excessive bleeding following surgery, trauma, dental procedures, or childbirth. Bleeding risk is particularly difficult to predict because FXI activity correlates poorly with clinical phenotype. With appropriate recognition of the disorder, individualised perioperative planning, and appropriate use of antifibrinolytic or replacement therapy when indicated, most patients can undergo surgery and childbirth safely.
Last update: September 2026
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