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CC Jan 2016 Heparin-Induced Thrombocytopenia

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echoecho's version from 2016-03-27 23:27

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Question Answer
Heparin-induced thrombocytopenia (HIT) occurs in about 1 in ______ hospital inpatients, although the incidence varies by the type of patient?5000
What patient group have a greater risk than medical patients?Surgical patients (espeically those undergoing cardiac or orthopedic surgery)
What gender have a higher risk?women have a higher risk then men
Which has a much higher risk for HIT (unfractionated heparin (UFH) vs low-molecular weight heparin (LMWH)?unfractionated heparin (UFH) has a higher risk
Paradoxically, HIT results in a _______ state, with a relatively high risk of what?prothromobotic; venous or arterial thrombosis
What is the pathogenesis of HIT?1) involves the binding of antibodies to complexes of platelet factor 4 (PF4) and heparin 2) the binding of these antibodies induces platelet activation, with release of large amounts of thrombin and other procoagulant factors 3) antibody binding also facilitates the clearance of platelets by the reticuloendothelial cells
*** Why is accurate dx of HIT critical?because underdiagnosis and overdiagnosis can expose patients to significant harm
In the absence of treatment, ____ ______ has been reported in 17-55% of patients with HIT and ____ ______ (including CVA and MI) occurs in 3-10% of HIT patients?venous thrombosis; arterial thrombosis
The nonheparin anticoagulants used to treat HIT are expansive and place patients at a risk of what?bleeding
What helps to determint he likelihood that thrombocytopenia is due to HIT?1) timing of the thrombocytopenia 2) degree of thrombocytopenia
In HIT, the platletes start to fall ____ to _____ days after exposure to heparin?5; 10
However the anti-PF4 antibodies responsible for HIT can persist in the circulation for up to _____ days?100
What is the sequelae of the above question?so an earlier onset can be seen in patients with a previous exposure to heparin within this time frame
The platelet count usually falls by > ____% from baseline, with a typical nadir in the range of what?50%; 40,000 to 80,000/mm3
What scoring system incorporates these and other factors to give a clinical estimate of the likelihood of HIT?4T scoring system
The 4T scoring system depends on what 4 characteristics?1) degree of thrombocytopenia 2) the timing 3) the presence or absence of thrombosis 4) likelihood of alternative causes of thrombocytopenia
Comment on the assays for anti-PF4 antibodies and why this test should not be ordered if the clinical suspicion is low?1) are highly sensitive for HIT but have low specificity particularly at lower concentrations
What other tests can be used which are highly specific, but their availability is limited?functional assays
*** In patients with high clinical suspicion for HIT, what should be done?1) all heparin products should be discontinued 2) a nonheparing anticoagulation should be started
Given the high risk of thrombosis, discontinuation of heparin alone is not sufficient. The American College of Chest Physicians recomends 3 nonheparin anticoagulants, list these and list which are in the US?1) Argatroban (Acova) is the only one available in the US 2) fondaparinux (Arixtra) for pregnant patients 3) bivalirudin (Angiomax) is for patients requirng urgent cardiac surgery
What transfusions should be avoided, as bleeding is rare in HIT, and what do these transfusion increase the risk of?1) platelet transfusion 2) thrombosis
*** Why should Warfarin not be used initially?because it inhibits the sysnthesis of proteins C and S and can exacerbate the risk of thrombosis
*** When can patients be transitioned to Warfarin use?after the platelet count has stabilized at a level > 150,000 but the tratment with an alternative anticoagulant should continue for a minimum of 5 days of overlap
Why does altnerative anticoagulants such as argatroban give a false impression that the full warfarin effect has been achieved in < 5 days and prompts early discontinuation?false positive elevated prothrombin times leading to increased risk of thrombosis
Anticoagulation should be continued for ____ weeks in patients with a simple HIT and up to ____ months if HIT is associated with a confirmed thrombotic event?4 weeks; 4 months
Explain the 4T Scoring system for HIT as to acute thrombocytopenia?2 points = platelt count decrease of > 50% AND nadir > 20,000; 1 point = platelet count decrease of 30-50% OR nadir 10,000 - 19,000; 0 points = platelet count decrease of < 30% OR nadir < 10,000
Explain the 4T Scoring system for HIT as to timing of onset?2 points = day 5-10 or day 1 if recent (last 100 days) prior heparin exposure; 1 point = after day 10 or unclear heparin exposure; 0 points = before or on day 4 with no recent heparin exposure
Explain the 4T Scoring system for HIT as to thrombosis (or other sequelae)?2 points = new thrombosis, skin necrosis or anaphylactoid reaction after heparin bolus; 1 point = progressive or recurrent thrombosis; 0 point = none
Explain the 4T Scoring system for HIT as to other causes of thrombocytopenia?2 points = none; 1 point = possible; 0 point = definite
Explain the 4T Scoring system for HIT as to scoring?1) high score = 6-8 points 2) intermediate score = 4-5 points 3) low score 0-3 points
*** SUMMARY = The risk of HIT is higher in what gender and what patient type? Heparin type?1)women; surgical patients (compared to medical patients) 2) higher risk for HIT if unfractionated heparin (UFH) is used compared to LMWH (low molecular weight heparin)
*** SUMMARY = Paradoxically, HIT results in a _______ state, with a relatively high ris of what?prothrombotic; venous or arterial thrombosis
*** SUMMARY = What 2 characteristics of the thrombocytopenia help to determin the likelihood of thrombocytopenia being due to HIT?1) timing of thrombocytopenia 2) degree of thrombocytopenia
*** SUMMARY = Anticoagulation should be continued for ___ weeks in patients with simple HIT and up to ___ months if HIT is associated with a confirmed thrombotic event?4 weeks; 4 months
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