Bleeding Disorder of Unknown Cause (BDUC)
“It’s a rare Bleeding disorder that general practitioners, consultants (other than Haematologists), dentists, and other health clinicians do NOT understand. Sometimes, they dismiss my condition because it has “Unknown Cause” in its title. I understand my condition more now. I can call my Treatment Centre for advice when needed.”
A heterogeneous bleeding disorder characterised by a clinically significant bleeding tendency in individuals with normal or non-diagnostic standard coagulation and platelet testing, where no specific inherited or acquired cause can be identified despite comprehensive evaluation.
Epidemiology
BDUC is one of the most common diagnoses among patients referred for evaluation of mild to moderate bleeding symptoms. Cohort studies from specialised haemostasis centres suggest that up to 30–50% of patients investigated for a bleeding tendency receive a diagnosis of BDUC.
Both sexes are affected, although women are overrepresented, largely due to gynaecological bleeding manifestations. The true population prevalence is unknown.
Clinical description
BDUC typically presents with mucocutaneous bleeding symptoms, most often beginning in childhood or adolescence, though diagnosis is frequently delayed until adulthood. Common manifestations include easy bruising, epistaxis, gingival bleeding, menorrhagia, postpartum haemorrhage, and excessive bleeding following dental work, surgery, or trauma.
Joint and deep muscle bleeding are uncommon and suggest an alternative diagnosis. Bleeding severity is usually mild to moderate but can be clinically significant, particularly in perioperative or obstetric settings. Many patients report a positive personal bleeding history with or without a positive family history. Bleeding scores (e.g. ISTH-BAT) are often elevated.
Etiology
The underlying cause of BDUC remains unknown. It is thought to represent a multifactorial disorder, potentially involving subtle defects in primary hemostasis, coagulation, fibrinolysis, vascular integrity, or currently unrecognised genetic variants.
Standard coagulation factor deficiencies, von Willebrand disease, platelet function disorders detectable by routine assays, and acquired causes of bleeding are excluded. Ongoing research suggests that some cases may eventually be reclassified as diagnostic techniques improve.
Diagnostic methods
BDUC is a diagnosis of exclusion. Diagnosis requires:
A convincing personal bleeding history, typically supported by an abnormal bleeding assessment tool score
Normal or non-diagnostic results on standard laboratory testing, including platelet count, PT, aPTT, fibrinogen, von Willebrand factor studies, and routine platelet function testing
Extended or specialised testing (e.g., specific rather than global assays, such as FVIII/FIX deficiencies, etc.; advanced platelet function tests; genetic testing) may be performed in expert centres but is not required to establish the diagnosis. Molecular testing is currently investigational and not diagnostic in most cases.
Differential diagnosis
Differential diagnoses include:
Mild von Willebrand disease
Mild coagulation factor deficiencies
Inherited platelet function disorders
Acquired bleeding disorders
Connective tissue disorders affecting vascular integrity
These must be carefully excluded before diagnosing BDUC.
Genetic counseling
No specific inheritance pattern has been established. Familial clustering may be observed, but genetic transmission remains undefined, and routine genetic counselling is not currently indicated.
BDUC
Prevalence
Unknown
Management and treatment
There are no disease-specific therapies. Management is individualised and based on bleeding phenotype and risk.
Treatment options include:
Antifibrinolytic agents (e.g. tranexamic acid) for mucosal bleeding and minor procedures
Desmopressin (DDAVP) in selected cases, particularly perioperatively
Hormonal therapy for the management of menorrhagia
Platelet transfusions or clotting factor concentrates are not routinely indicated but may be considered in exceptional circumstances
A written bleeding management plan is recommended, particularly for surgery, dental procedures, and childbirth.
Prognosis
Prognosis is generally good. Most patients experience mild to moderate bleeding, which can be effectively managed with anticipatory planning and supportive treatment. Long-term outcomes are favourable, though quality of life may be impacted by recurrent bleeding and diagnostic uncertainty.
Last update: February 2026
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