Disseminated intravascular coagulation
Breakdown · Consumptive Low fibrinogen High D-dimer
Unregulated systemic tissue factor exposure drives thrombin generation throughout the microvasculature. Fibrin is laid down in small vessels while platelets, fibrinogen and the natural anticoagulants are consumed and secondary fibrinolysis is switched on, so the same patient thromboses and bleeds simultaneously. It is always secondary — the diagnosis is incomplete until the trigger is named.
Traced from the start
- Tissue factor and the extrinsic triggerVitamin K cycle and gamma-carboxylation
- Contact activation system (factor XII, prekallikrein, high-molecular-weight kininogen)
- Subendothelial collagen and von Willebrand factor
- Tissue factor-factor VIIa complex (extrinsic tenase)Factor IXaFactor VIIIa and its von Willebrand factor carrierActivated platelet phospholipid surface
- Factor XaFactor VaProthrombin (factor II)
- Thrombin (factor IIa)
- Cross-linked fibrin clot
- Disseminated intravascular coagulation
Detail
- Triggers
- Sepsis (especially Gram-negative), major trauma and burns, obstetric catastrophe (placental abruption, amniotic fluid embolism, retained dead fetus, HELLP), malignancy (mucinous adenocarcinoma, acute promyelocytic leukaemia), haemolytic transfusion reaction and snake envenomation
- Laboratory pattern
- Thrombocytopenia, prolonged PT and APTT, low and falling fibrinogen, markedly raised D-dimer, and schistocytes on the blood film
- Versus liver failure
- Both prolong the PT and drop platelets, but factor VIII is normal or high in liver disease and low in DIC, because factor VIII is made by endothelium rather than hepatocytes
- Versus TTP
- TTP also gives thrombocytopenia and schistocytes but with a normal PT, APTT and fibrinogen
- Management
- Treat the underlying cause; give platelets, fresh frozen plasma and cryoprecipitate only for active bleeding or before a procedure; heparin only in the predominantly thrombotic phenotype
When it goes wrong
Acute promyelocytic leukaemia, whose granules release procoagulants and whose blasts express annexin II driving hyperfibrinolysis
Catastrophic haemorrhage at presentation and during induction; all-trans retinoic acid is started on clinical suspicion, before cytogenetic confirmation of t(15;17)
Placental abruption or amniotic fluid embolism
Rapid-onset DIC with postpartum haemorrhage; fibrinogen falls early and predicts severity, so cryoprecipitate or fibrinogen concentrate is given early rather than waiting for the coagulation screen
Practise this structure
1 question in the bank tagged Fibrinolysis.