Heparin-Induced Thrombocytopenia (HIT)

HIT is an immune-mediated adverse effect of heparin that paradoxically increases risk of thrombosis Heparin-Induced Thrombocytopenia (HIT)

HIT is a clinico-pathological syndrome Thrombocytopenia and/or Thrombosis Warkentin TE, Chong BH, Greinacher A. Thromb Haemost 1998;79:1-7. Greinacher et al. Blood 2005;106: Greinacher et al. Thromb Haemost 2005;94: Clinical Pathological Heparin-dependent, platelet-activating IgG antibodies

Anaphylactoid reaction after i.v. heparin bolus Skin lesions at s.c. heparin injection sites Overt (decompensated) disseminated intravascular coagulation (DIC) Heparin-induced thrombocytopenia (HIT) Less frequent clinical manifestations

Approach to diagnose HIT T hrombocytopenia (> 50% decrease) T iming 5-14 days after starting heparin Unusual thromboembolism; skín lesions; anaphylaxis O T her cause not apparent T est for HIT antibodies positive (usually strongly positive) Yes HIT Strongly Suspected Possible T hrombosis Confirmed when positive in context of strong clinical suspicion

Clinical events associated with HIT Venous thrombosis (30-70%) Deep vein thrombosis (DVT) Pulmonary embolism (PE) Adrenal necrosis (adrenal vein thrombosis) Cerebral venous (sinus) thrombosis Venous limb gangrene (VKA associated) Arterial thrombosis (“white clots”) (15-30%) Limb artery thrombosis Stroke Myocardial infarction Skin lesions at heparin injection sites (10%) Skin necrosis Erythematous plaques Acute reactions after i.v. heparin bolus (10%) Disseminated intravascular coagulation (DIC) (10%)

Drugs associated with HIT Unfractionated heparin Prophylactic dose Therapeutic dose Flushes Heparin-coated devices Low-molecular-weight heparin Prophylactic dose Therapeutic dose Other highly sulfated polysaccharides Pentosan polysulfate Hypersulfated chondroitin sulfate PI-88 (anti-angiogenic drug)

Ring of positive charge HIT: a link between immune system and hemostasis Fc  RIIa Heparansulfate PF4 Heparin B-L Warkentin TE, Chong BH, Greinacher A. Heparin induced thrombocytopenia: Towards consensus. Thromb Haemost 1998,79:1-7 Thrombin Tissue factor EC Li et al, Blood 2002; 99:1230 Thrombosis PF4 tetramer

Sequence of events in the development of HIT Current or recent exposure to heparin Immune response against platelet factor 4 (PF4)/heparin complexes Anti-PF4/heparin IgG antibodies crosslink platelet Fc receptors and trigger platelet activation Positive feedback for platelet activation (e.g., adenosine diphosphate, thromboxane A 2 ) Platelet activation results in shedding of procoagulant platelet microparticles Initiation

Sequence of events in the development of HIT Platelet microparticles promote thrombin generation Endothelial cell injury and monocyte activation further enhance thrombin generation PF4 release neutralizes heparin PF4 release leads to formation of additional PF4/heparin complexes, exposing more antigens, and thus further amplifying platelet activation Development of a hypercoagulable state

HIT - a vicious cycle of platelet activation and coagulationPF4/Heparin/HIT-IgG Platelet Activation Coagulation Release PF4 Monocyte Activation Coagulation Endothelial Cell Injury Thrombosis Embolism Morbidity&Death Platelet Activation Release PF4 /HIT-IgG PF4

Factors influencing frequency of HIT FactorInfluence Type of heparin Bovine UFH > porcine UFH > LMWH Patient population Post-surgery > medical > obstetrical Duration of heparin 5 or more days heparin use > 1-4 days Dose of heparin Change from low to full dose can lead abrupt platelet  in immunized patient Gender Female > male Definition of thrombocytopenia Proportional platelet count fall (e.g. >50%) more sensitive than absolute platelet 

“Iceberg model” of HIT Thrombocytopenia Positive washed platelet activation assay Positive PF4 antigen assay Thrombosis HIT syndrome Numbers of Patients Adapted from Warkentin TE. Br J Haematol 2003,121:535 HIT and associated thrombosis occurs in the subset of patients with platelet-activating anti-PF4/H antibodies

Platelet count nadir distribution in HIT Adapted from Warkentin TE. Br J Haematol 2003,121:535 Median platelet count nadir 55 x 10 9 /L Platelet fall <50% Platelet Count Nadir (x 10 9 /L) Number of Patients Type of HIT- associated thrombosis Nil (N=72) Venous (N=132) Venous & arterial (N=6) Arterial (N=24) 5 >400

Management of HIT – diagnosis Three different clinical presentations Adapted from Warkentin TE. Br J Haematol 2003, 121: 535

Detection of HIT antibodies Platelet activation assays Serotonin release assay (SRA; uses “washed” platelets) Heparin-induced platelet activation (HIPA) assay (uses “washed” platelets) Platelet aggregation test (PAT; uses citrate-anticoagulated platelet-rich plasma) Platelet microparticles (flow cytometry) Antigen assays PF4/heparin-enzyme immunoassay (EIA) PF4/polyvinyl sulfonate EIA Fluid-phase EIA Particle gel immunoassay

Detection of HIT antibodies Specificity (%) Diagnostic assaySensitivity (%) Early platelet  Late platelet  Serotonin release assay (SRA) 90-98> Heparin-induced platelet activation assay (HIPA) 90-98> Platelet aggregation (PRP) PF4/heparin EIA>90> Combination of platelet activation assay & PF4 antigen EIA 100> Adapted from 7th. ACCP Conference 2004 Chest 126, 311S

Detection of HIT antibodies High negative predictive value Negative test usually rules out HIT * Moderate positive predictive value Stronger test result = higher chance of HIT Routine antibody testing is NOT recommended unless: Thrombocytopenia or >50%  in platelet count Thrombosis Heparin-induced skin necrosis Other sequelae of HIT * Applies to solid-phase EIAs and washed platelet activation assays 7th. ACCP Conference 2004 Chest 126, 311S

Clinical signs of HIT Erythematous plaques 1 Skin necrosis 1 Venous gangrene 2 Deep venous thrombosis 1 1 Reproduced with permission Blackwell Publishing (Warkentin TE. Br J Haematol Warkentin TE et al. Ann Intern Med 1997

Clinical signs of HIT Fever, chills, flushing Respiratory distress Hypertension, tachycardia, chest pain Transient global amnesia, headache Deep vein thrombosis Pulmonary embolism Limb ischemia and infarction Thrombotic stroke and cerebral (sinus) vein thrombosis Myocardial infarction Adrenal necrosis Acute reactions after intravenous heparin bolus Venous and/or arterial thrombosis

Differential diagnosis Hemodilution post-surgery Severe pulmonary embolism Sepsis DIC (multiple causes besides HIT) Cancer-associated DIC Antiphospholipid syndrome Thrombolytic therapy EDTA-induced pseudothrombocytopenia GP IIb/IIIa inhibitor-induced thrombocytopenia Drug-induced thrombocytopenia (other than heparin) Post-transfusion purpura Thrombotic thrombocytopenic purpura Non-immune heparin-associated thrombocytopenia

Platelet count monitoring is recommended in patients at risk of HIT > 0.1%* Platelet count monitoring Patient populationYes/NoFrequency Risk for HIT common (>1%) Receiving therapeutic dose UFHYes min. alternate day  14 d Receiving post-op prophylactic dose UFHYesmin. alternate day d Starting UFH/LMWH & have received UFH in last 100 d or exposure uncertain Yesbaseline value-repeat in 1 d Systemic reaction after UFH bolusYes immediate – compare with pre-bolus value Risk for HIT infrequent (0.1-1%). Medical/Obstetric UFH; Post-op LMWH; Post-op UFH ‘flush’; LMWH after UFH Yesevery 2 -3 days, d Risk HIT < 0.1%. Medical/obstetric patients on LMWHNo- * 7th. ACCP Conference 2004 Chest, 126: 311S

210 T hrombocytopenia > 50% platelet count fall to nadir ≥ % platelet count fall to nadir <30% platelet count fall to nadir ≤ 10 T iming of fall in platelet count or other sequelae Onset d 5-10 or < 1 d (if heparin exposure within 30 d) > d 10, or timing unclear, or < d 1 with recent heparin d Platelet count fall < d 4 (without recent heparin exposure) T hrombosis or other sequelae New thrombosis; skin necrosis; post-heparin bolus acute systemic reaction Progressive or recurrent thrombosis; erythematous skin lesions; suspected thrombosis – not confirmed None O T her cause for thrombocytopenia No other cause for platelet count fall is evident Possible other cause is evident Definite other cause is present Points: Score 0, 1 or 2 for each of 4 categories: Diagnosis - pretest probability: the 4 T’s A B C D Adapted from Lo et al. J Thromb Haemost 2006, in press

Diagnosis - pretest probability Interpretation of 4 T’s score Score 0-3 : very unlikely to be HIT (<5%) Score 4 - 5: a minority have HIT (10-30%) Score 6 – 8: 20 to >80% have HIT, depending on the clinical setting and scorer´s experience: these patients usually require an alternative, non-heparin anticoagulant in therapeutic doses Adapted from Lo et al. J Thromb Haemost 2006, in press

Management of HIT – treatment Stop heparin (UFH/LMWH), even in patients without thrombosis Initiate alternative non-heparin anticoagulant because of high risk of symptomatic thrombosis Test for HIT antibodies Duplex ultrasonography for lower-limb DVT When HIT is strongly-suspected:

Management of HIT – treatment Do not start a vitamin K antagonist (VKA) - if started prior to diagnosis it should be reversed by vitamin K * Do not use low-molecular-weight heparin (LMWH) Do not give platelet transfusions unless needed to manage serious hemorrhage * Recommendation to give vitamin K applies particularly to direct thrombin inhibitors (DTIs), because prolongation of the aPTT by warfarin can lead to underdosing of DTI therapy (in contrast, danaparoid is not monitored by aPTT) When HIT is strongly-suspected: 7th. ACCP Conference 2004 Chest, 126: 311S-337S Warkentin TE. J Thromb Haemost 2006; in press.

Management of HIT – treatment Postpone starting overlapping coumarin until the platelet count has recovered to at least 100 (and preferably) 150 x 10 9 /L Therapeutic doses of alternative, non-heparin anticoagulants are usually required If a sensitive test for HIT is negative, heparin therapy may be re-started with regular platelet count monitoring When the diagnosis of HIT is confirmed: * 7th. ACCP Conference 2004 Chest, 126, 311S-337S

Management of HIT – treatment If the patient requires therapeutic dose anticoagulation for non-HIT reasons, use alternative anticoagulant in therapeutic dose. If patient does not require therapeutic dose anticoagulation for non-HIT reasons, consider prophylactic-dose alternative anticoagulation, e.g. danaparoid 750 U b.i.d. or t.i.d. until HIT antibody test results are available. When HIT is clinically possible but platelet count decrease is more likely caused by other reasons: Selleng K and Greinacher A: Intensiv up-2-date 2005;1:

Adapted from Warkentin TE, Kelton JG. Am J Med. 1996;101:502–507. Occurrence of symptomatic thrombosis after stopping heparin in patients confirmed to have isolated HIT Cumulative thrombotic event-rate (%) Days after isolated HIT recognized 52.8% N = year retrospective study

Odds ratios for risk of thrombosis Prothrombin anomaly 2.0 Lupus anticoagulant 5.4 Factor V Leiden6.6 Protein S deficiency 10.9 Dysfibrinogenaemia 11.3 Protein C deficiency14.4 Antithrombin deficiency24.1 HIT Warkentin TE. Can J Cardiol 1995;11(Suppl. C):29C-34C Warkentin TE. Thromb Res; 2003; 110:73-82

Management of HIT – treatment Danaparoid – Xa/IIa inhibitor (anti-Xa >> anti-IIa) Direct thrombin inhibitor (DTI): Lepirudin Argatroban Bivalirudin Suitable alternative non-heparin antithrombotic therapies are: * 7th. ACCP Conference 2004 Chest 126: 311S-337S

HIT – summary & conclusions 1.HIT is a potentially fatal side effect of heparin that is more common with UFH than LMWH 2.HIT is a clinico-pathologic syndrome: its diagnosis is based on compatible clinical features and presence of HIT antibodies 3.Antibodies against PF4/heparin are formed commonly during heparin treatment; HIT occurs in the subset of patients with strong platelet- activating IgG antibodies

4.Binding of HIT antibodies to PF4/heparin complexes on the platelet surface results in platelet activation, thrombocytopenia and increased risk of arterial thrombosis 5.Platelet, monocyte, and endothelial cell activation results in a hypercoagulable state, and increased risk of venous thrombosis 6.HIT-associated thrombosis occurs in some patients 1 – 2 days before platelet counts decrease HIT – summary & conclusions

7.Platelet count monitoring is important to diagnose isolated HIT and thus has the potential to prevent thrombosis 8.Recognizing a relative decrease of platelet count is important since platelets do not always fall below 150 x 10 9 /L 9.Platelet count monitoring is recommended in most patients receiving UFH and in some patients receiving LMWH. HIT – summary & conclusions

9.Heparin should be stopped immediately in all situations where HIT is strongly suspected 10.Due to the high risk of thrombosis in patients with HIT anticoagulation with a non-heparin anticoagulant should be started even in the absence of overt thrombosis 11.Danaparoid provides an option for anticoagulation in either prophylactic or therapeutic doses HIT – summary & conclusions

Heparin-Induced Thrombocytopenia (HIT)