Thrombosis Knowledge Centre

Pharmacological Options

Complications of Treatment

Bleeding risk

The major complication of antithrombotic therapy is bleeding. For each antithrombotic drug, the antithrombotic efficacy must be balanced against the potential increased bleeding risk.

Clinical trials distinguish:

Major bleeding: clinically overt bleeding associated with a decrease of ≥2 g/dL in the haemoglobin level, leading to the transfusion of ≥2 units of red cells or whole blood, occurring in a critical organ, or contributing to death
Clinically relevant non-major bleeding: clinically relevant bleeding not qualifi ed as major (e.g. epistaxis requiring intervention, large cutaneous haematomas, or spontaneous macroscopic haematuria)
Minor bleeding: all other bleeds

The criteria for defining the severity of bleeding vary considerably between studies, accounting in part for the variation in the rates of bleeding reported.

Heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a severe immuno-allergic adverse effect of heparin therapy mediated by antibodies, mostly antibodies against PF4 (platelet factor 4)/heparin complexes. HIT is most common in patients receiving UFH (0.5 to 5%), but also occurs in patients receiving LMWH (Jang and Hursting. Circulation 2005;111:2672-83).

Thrombosis rather than haemorrhage is the predominant clinical sign. If untreated:

38 to 76% of patients with biological HIT develop venous and arterial thromboembolic complications
Among HIT patients with thrombosis, 9 to 11% require a limb amputation and 17 to 30% die (Jang and Hursting. Circulation 2005;111:2672-83)