HIT

Question 1

HIT results from an autoantibody directed against endogenous platelet factor 4 (PF4) in complex with heparin, it Usually requires exposure of _____ for several days

Answer 1

heparin

Question 2

HIT’s autoantibody activates platelets and can cause _____.

Answer 2

catastrophic arterial and venous thrombosis

Question 3

mortality rate of HIT

Answer 3

2-20%

Question 4

Once HIT antibodies bind to PF4 on platelet surface, their Fc region is captured by Fc receptors on surface of same or adjacent platelets.
This creates a positive feedback loop of further ______.

Answer 4

platelet activation

Question 5

HIT: Thrombocytopenia is Mainly caused by ?

Answer 5

removal of IgG-coated platelets by macrophages of the reticuloendothelial system (e.g., spleen, liver, bone marrow)

Question 6

HIT: Thrombosis potential causes

Answer 6

o Release of procoagulant substances from activated platelets
o Release of platelet microparticles (i.e., fragments derived from the platelet membrane) that can catalyze clot formation
o Endothelial cell activation
o Endothelial cell injury induced by binding of HIT antibodies to heparan sulfate on endothelial cell surfaces, leading to increased tissue factor and thrombin generation
o Endothelial cell release of adhesion molecules (e.g., interleukin-6, von Willebrand factor)
o Activation of monocytes by HIT antibodies
o Alteration of other aspects of the coagulation cascade by HIT antibodies (e.g., reduced generation of activated protein C)

Question 7

what heparin dose is needed for HIT to occur?

Answer 7

HIT can occur with any heparin dose, schedule, and administration route

Question 8

Ultralarge complexes form most efficiently with what kind of heparin?

Answer 8

unfractionated heparin

Question 9

HIT IS Reported in up to WHAT PERCENT of patients exposed to heparin for more than four days?

Answer 9

5%

Question 10

Risk factors for HIT

Answer 10

Ð	UFH (~3%) v. LMWH (<1%) in surgical patients (not proved in medical patients)
Ð	Higher doses
Ð	Female gender
Ð	Surgery
Ð	Older age

Question 11

most common manifestation of HIT

Answer 11

thrombocytopenia

Question 12

thrombocytopenia occurs when platelet count is

Answer 12

<150,000/microL or

A platelet count drop of >50% of baseline

Question 13

is bleeding common with Thrombocytopenia

Answer 13

• Bleeding is rare because the platelet count nadir typically does not drop below 20,000/microL

Question 14

HIT- Thrombocytopenia Onset typically occurs _____ after the initiation of heparin therapy

Answer 14

5 to 10 days

Question 15

Early onset of HIT (i.e., thrombocytopenia within the first 24 hours of exposure) may be seen if the patient has been exposed to heparin in the previous one to three months and has circulating______.

Answer 15

HIT antibodies

Question 16

• The resolution of thrombocytopenia following withdrawal of heparin typically occurs within__.

Answer 16

7 days

Question 17

Delayed-onset HIT: rarely (but with increasing frequency) thrombocytopenia and thrombosis can occur___ after heparin has been withdrawn (need thorough medication history in patients developing S/Sx)

Answer 17

1-2 weeks

Question 18

HIT: Thrombosis

Occurs in up to what percentage of individuals with HIT

Answer 18

50%

Question 19

Common sites of venous thrombosis include______.

Answer 19

leg veins, cardiac vessels, and skin

Question 20

Arterial thrombosis has been reported in the ______.

Answer 20

heart, central nervous system, limbs, and internal organs

Question 21

• Complications of thrombosis include ?

Answer 21

skin necrosis, limb gangrene (sometimes requiring amputation), and organ infarction

Question 22

Acute systemic anaphylactic reactions have been described in patients with HIT, and these can be fatal. Affected patients may have what symptoms?

Answer 22

fever, respiratory compromise, and/or hypertension

Question 23

HIT: Monitoring

Answer 23

• Frequent (daily or every 2d) PLT count
• If at high risk ) then enzyme immunoassays for antibodies to PF4-heparin complexes or heparin-dependent platelet activation can be ordered
• EIAs should be ordered before treatment if patient is high risk but should NOT delay therapy

Question 24

____ has the potential to prevent thrombotic events, which are the major cause of morbidity and mortality in patients with HIT

Answer 24

early intervention

Question 25

HIT: Treatment Overview

Answer 25

1. Stop and avoid all heparin products- forever
2. Give a non-heparin alternative anticoagulant
3. Postpone warfarin pending substantial PLT count recovery
4. Test for HIT antibodies
5. Investigate for lower limb DVT
6. Avoid prophylactic PLT transfusion

Question 26

To reduce thrombotic complications, administer a different, non-vitamin K-dependant anticoagulant such as _______.

Answer 26

argatroban, bivalirudin, or fondaparinux until PLT >150/mcL

Question 27

Warfarin should not be used as the initial anticoagulant since warfarin therapy may increase the risk of?

Answer 27

increase the risk of venous limb gangrene in patients with deep vein thrombosis through its rapid lowering of protein C levels

Question 28

Warfarin should be started in a patient with HIT only when both of the following have been accomplished

Answer 28

o The patient has been stably anticoagulated with an alternative anticoagulant
o The platelet count has increased to at least 150,000/microL

Question 29

• The starting dose of warfarin should be a low maintenance dose of ≤5 mg/day rather than a high initial or loading dose (e.g., ≥10 mg/day), to minimize the transient hypercoagulable state induced by the rapid decline in______

Answer 29

protein C levels

Question 30

Warfarin must be monitored by the prothrombin time (PT) with international normalized ratio (INR)
The target range for anticoagulation should be an INR in the range of ___ to ____.

There should be a minimum of ___ of overlapping therapy before the alternative anticoagulant is discontinued

Answer 30

2.0 to 3.0

5 days

Question 31

• Patients diagnosed with HIT based on clinical and laboratory data should avoid ____ for life

Answer 31

heparin

Question 32

Sources of heparin include

Answer 32

o Heparin flushes (e.g., for arterial lines or heparin locks)
o Heparin-bonded catheters
o Heparin-containing medications (e.g., some forms of prothrombin complex concentrates [PCCs])
o LMWHs (e.g., enoxaparin, dalteparin, tinzaparin) and UFH