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.

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.