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==Definition==
==Definition==

Revision as of 15:36, 2 January 2014

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Karol Gema Hernandez, M.D. [2], Rim Halaby, M.D. [3]

Definition

Heparin induced thrombocytopenia (HIT) is an antibody-mediated adverse drug reaction that predisposes to elevated risks of arterial and venous thromboembolism.

  • Typical-onset HIT: within 5 to 10 days following the initiation of heparin
  • Early-onset HIT: within 24 hours following the initiation of heparin
  • Delayed-onset HIT: up to 3 weeks following the cessation of heparin[1]


  • HITT: Heparin induced thrombocytponia with thrombosis
  • Isolated HIT: Heparin induced thrombocytponia without evidence of thrombosis[1]

Causes

Life Threatening Causes

Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.

Common Causes

Screening for HIT

 
 
Asses the risk of HIT
 
 
 
 
 
 
 
 
 
 
 
 
Patient Population (Minimum of 4-d Exposure)Incidence of HIT, %
Postoperative patients
Heparin, prophylactic dose1-5
Heparin, therapeutic dose1-5
Heparin, flushes0.1-1
LMWH, prophylactic or therapeutic dose0.1-1
Cardiac surgery patients1-3
Medical patients
Patients with cancer1
Heparin, prophylactic or therapeutic dose0.1-1
LMWH, prophylactic or therapeutic dose0.6
Intensive care patients0.4
Heparin, flushes< 0.1
Obstetrics patients <0.1
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Risk <1%
 
Risk >1%
 
 
 
 
 
 
 
 
 
 
❑ Do not monitor platelet count
 
❑ Monitor platelet count every 2 or 3 days from day 4 to day 14 (or until heparin is stopped)

Algorithm based on the 2012 ACCP evidence based clinical practice guidelines.[1]

Diagnostic Approach to HIT

 
 
 
Thrombocytopenia
❑ Platelet count <150,000/mm3, OR
❑ >30-50% decrease decrease of platelet from baseline
❑ Recent heparin or LMWH use in the previous 5- 14 days
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Characterize the symptoms (if present):
❑ Arterial thromboembolism
❑ Venous thromboembolism
❑ Unusual manifestations:

- Skin necrosis at SC heparin injection sites
- Transient global amnesia

❑ Absence of petechiae and/or significant bleeding
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Suspicion of HIT
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Low clinical probability
 
 
 
Intermediate/high clinical probability
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Unlikely HIT
❑ Consider alternative diagnoses
❑ Continue heparin
 
 
 
❑ Discontinue heparin
❑ Begin alternative anticoagulation
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
❑ Order anti PF4 antibodies
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Moderately/strongly positive test
 
Weakly positive test
Plus
High clinical probability
 
Weakly positive test
PLUS
Intermediatre clinical probability
 
Negative
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
❑ Order functional assay
 
 
 
 
 
Unlikely HIT
❑ Consider alternative diagnoses
❑ Continue heparin
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Positive test
Likely HIT
 
Negative test
HIT undetermined
 
 
 
 
 
 
 
 


The most studied functional assays are serotonin release assay (SRA) and Heparin induced platelet activation assay (HIPA).[2]

The diagnostic algorithm is based on "How I treat heparin-induced thrombocytopenia" from Blood (2012).[2]

Special Considerations

Shown below is a table summarizing the appropriate choice of anticoagulation therapy in special situations.[1]

Special situations Acute HIT or subacute HIT (normal platelets and positive antibodies) Past medical history of HIT
Cardiac surgery Urgent cardiac surgery: Use bivalirudin
Non urgent cardiac surgery: Delay the surgery until HIT has resolved and antibodies are negative
Negative antibodies: Use heparin (short term)
Positive antibodies: Use bivalirudin
PCI Use bivalirudin or argatraban Use bivalirudin or argatraban
Renal replacement therapy Use argatroban or danaproid Use regional citrate
Pregnancy Use danaproid -

Do's

  • In case of severe thrombocytopenia among patients with HIT, administer platelet transfusions when the patient is bleeding or when performing procedures associated with an elevated risk of bleeding.[1]

References

  1. 1.0 1.1 1.2 1.3 1.4 Linkins LA, Dans AL, Moores LK, Bona R, Davidson BL, Schulman S; et al. (2012). "Treatment and prevention of heparin-induced thrombocytopenia: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines". Chest. 141 (2 Suppl): e495S–530S. doi:10.1378/chest.11-2303. PMC 3278058. PMID 22315270.
  2. 2.0 2.1 Cuker A, Cines DB (2012). "How I treat heparin-induced thrombocytopenia". Blood. 119 (10): 2209–18. doi:10.1182/blood-2011-11-376293. PMID 22246036.