Coagulation factors, anticoagulant proteins, and fibrinolytic proteins are important for haemostasis and may be altered by inherited and acquired conditions. Common causes of coagulopathies include vitamin K (VK) deficiency (VKD), liver disease, lupus anticoagulants, consumption or disseminated intravascular coagulation, and much less commonly, an inherited or an acquired autoimmune coagulopathy. VKD typically accounts for ≥30% of all coagulopathy referrals, and VKD is particularly common among infants but can occur at any age and in combination with other coagulopathies. Tests for fibrinogen help assess both congenital and acquired coagulopathies, with low levels predictive of poor outcomes from diverse conditions including trauma and postpartum haemorrhage. Inherited factor deficiencies are rarer, and some affect multiple coagulation factors (F), such as combined FV and FVIII deficiency, familial deficiencies of VK-dependent clotting factors, and congenital disorders of glycosylation. Additionally, there are some rare but important disorders that uniquely impair the procoagulant/anticoagulant balance, including F5 mutations that markedly increase tissue factor pathway inhibitor in plasma, causing prolonged prothrombin and activated partial thromboplastin times, without factor deficiencies. THBD mutations that increase functional, soluble thrombomodulin in plasma can also cause bleeding. Other THBD mutations cause thrombomodulin deficiency and a consumptive coagulopathy. Bleeding disorders that result from pathogenic changes to fibrinolysis include autosomal recessive, loss-of-function mutations in SERPINE1 and SERPINF2 and an autosomal dominant gain-of-function mutation affecting PLAU, in the case of Quebec platelet disorder, which causes platelet-dependent increased fibrinolysis. Laboratories need to consider strategies for diagnosing these different conditions.

Hyperfibrinolysis is rarely investigated as an underlying mechanism in patients with mild-to-moderate bleeding disorders (MBDs) and bleeding disorders of unknown cause (BDUC). Hereditary hyperfibrinolytic disorders, including α2-antiplasmin (α2-AP) deficiency, plasminogen activator inhibitor type 1 (PAI-1) deficiency, Quebec platelet disorder, and tissue plasminogen activator (tPA) excess, present with mild-to-moderate bleeding symptoms that are common in patients with MBD or BDUC, but may also manifest as life-threatening bleeding. This review summarizes the available data on hyperfibrinolysis in MBD and BDUC patients, and its assessment by various methods such as measurement of fibrinolytic factors, global hemostatic assays (e.g., viscoelastic testing, turbidity-based plasma clot lysis), and fluorogenic plasmin generation (PG). However, evidence on the relationship between hyperfibrinolytic profiles and bleeding severity is inconsistent, and, although found in some coagulation factor deficiencies, has not been universally observed. In BDUC, increased tPA activity and paradoxical increases in thrombin-activatable fibrinolysis inhibitor and α2-AP have been reported. Some studies reported no change in PAI-1 levels, while others observed reduced PAI-1 levels in a significant subset of patients. The tPA-ROTEM (tPA-rotational thromboelastometry) assay identified a hyperfibrinolytic profile in up to 20% of BDUC patients. PG analysis revealed a paradoxically reduced peak plasmin, but showed strong predictive power in differentiating BDUC patients from healthy controls. Although global fibrinolytic assays may help identify hyperfibrinolytic profiles as a potential cause of increased bleeding in some MBD or BDUC patients, the utility of measuring fibrinolytic factors requires further investigation. Tranexamic acid is commonly used to treat hereditary hyperfibrinolysis and is also recommended in MBD/BDUC patients prior to hemostatic challenges.

Fibrinolysis is initiated by the activation of plasminogen to plasmin via tissue-plasminogen activator (tPA) and urokinase-plasminogen activator (uPA); plasmin then converts fibrin to fibrin degradation products (FDPs). The antifibrinolytics counterbalancing this system include plasminogen activator inhibitor-1 (PAI-1), which inhibits tPA and uPA, α-2 antiplasmin (α2AP), which inhibits plasmin, and thrombin activatable fibrinolysis inhibitor, which inhibits the conversion of fibrin to FDP. Inherited disorders of the fibrinolytic pathway are rare and primarily have hemorrhagic phenotypes in humans: PAI-1 deficiency, α2AP deficiency, and Quebec platelet disorder. Patients with these disorders are usually treated for bleeds or receive prophylaxis to prevent bleeds in the surgical setting, with pharmacological antifibrinolytics such as aminocaproic acid and tranexamic acid. Disorders of the fibrinolytic pathway with fibrin deposition are extremely rare, mostly noted in patients with plasminogen deficiency, who have more recently benefited from advances in human plasma-derived plasminogen concentrates administered intravenously or locally. These disorders can be very difficult to diagnose using conventional or even specialized coagulation testing, as testing can be nonspecific or have low sensitivity. Testing of the corresponding protein's activity and antigen (where applicable) can be obtained in specialized centres, and routine laboratory measures are not diagnostic. Genetic testing of the pathogenic mutations is recommended in patients with a high suspicion of an inherited disorder of the fibrinolytic pathway.