Heparin Induced Thrombocytopaenia

Heparin Induced Thrombotic Thrombocytopaenia Syndrome (HITTS)

22/1/11

PY Mindmaps

= an immune mediated hypersensitivity reaction to platelet factor 4/heparin complex -> platelet activation and hypercoagulability

- incidence 0.1-1%

CLINICAL FEATURES

- thrombocytopaenia (often 5-10 days post heparin)

- thrombosis

- skin necrosis

- systemic reaction after IV UFH

Risk factors

- related to amount of heparin exposure

- UFH > LMWH

- surgical patients > medical

Scoring system for likelihood pretest probability

- severity of thrombocytopaenia

- timing of onset of platelet decrease (recent exposure increases risk)

- thrombosis (recent proven increases risk)

- other reason for platelet decrease

INVESTIGATIONS

- ELISA antibody assays:

-> PF4/polyanion EIA

-> detects antibodies reactive against the PF4/Heparin complex (IgM, IgG and IgA)

-> IgG is the most sensitive for disease

-> high sensitivity (90-98%) and low specificity

-> > 1.0 optical density units = more likely to be HITT

-> <1.0 optical density units = then a functional assay should be performed

- functional assays: detects antibodies on their ability to activate platelets in the presence of heparin

- U/S of limbs looking for DVT: DVT have often developed prior to development of thrombocytopaenia.

MANAGEMENT

Principles

(1) Avoid and discontinue all heparin (including LMWH)

(2) Administer non-heparin alternative anticoagulant

(3) Anti-PF4/heparin antibody test for confirmation

(4) Avoid platelet transfusion

(5) Await platelet recovery before initiation of warfarin

(6) Assess for lower extremity DVT

Specific

- danaparoid: heparinoid with predominant anti-Xa activity, 10-20% cross reactivity with HIT’s antibodies but not clinically significant

- lepirudin: direct thrombin inhibitor, dose adjust in renal impairment, significant relative risk reduction in death, amputation and new thrombotic complications when used in HITTS

- warfarin: reduction in protein C synthesis -> increase in clinical condition thus delay until danaparoid or lepirudin is therapeutic and platelet count has recovered

COMPLICATIONS

- venous thrombosis

- arterial thrombosis

- skin necrosis at sights heparin is injected

- acute systemic reactions after IV bolus (may look like anaphylaxis)

- decompensated DIC

- death (10-30%)

Jeremy Fernando (2011)