Diagnostic Criteria for Heparin-Induced Thrombocytopenia (HIT)
- Heparin exposure >5 days
- Relative thrombocytopenia: decrease in platelet count by 50% from baseline OR absolute thrombocytopenia: decrease in platelet count to less than 100 to 150 x 109/L
- Absence of other causes of thrombocytopenia
- Development of new thrombosis, or extension of pre-existing thrombosis, while receiving heparin therapy
- Confirmation by laboratory testing
- Return to normal platelet count when heparin is discontinued
Serology tests to determine HIT (listed in order of greatest to lowest sensitivity)
- Serotonin release assay
- Heparin/PF 4 ELISA
- Platelet aggregation
Estimating the Pretest Probability of HIT: The “Four T’s”
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Points (0, 1, or 2 for Each of 4 Categories: Maximum Possible Score = 8) |
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2 |
1 |
0 |
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Thrombocytopenia |
>50% Platelet fall to nadir >/= 20 |
30–50% Platelet fall, or nadir 10-19 |
<30% Platelet fall, or nadir <10 |
|
Timing* of onset of platelet fall (or other sequelae of HIT) |
Days 5–10, or </= day 1 with recent heparin (past 30 days) |
>Day 10 or timing unclear; or <day 1 with recent heparin (past 31–100 days) |
<Day 4 (no recent heparin) |
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Thrombosis or other sequelae |
Proven new thrombosis; skin necrosis; or acute systemic reaction after intravenous UFH bolus |
Progressive or recurrent thrombosis; erythematous skin lesions; suspected thrombosis (not proven) |
None |
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OTher cause(s) of platelet fall |
None evident |
Possible |
Definite |
UFH, Unfractionated heparin
Pretest probability score: 6–8 indicates high; 4–5, intermediate; and 0–3, low.
*First day of immunizing heparin exposure considered day 0.
References:
- Warkentin TE, Aird WC, Rand JH. Platelet-endothelial interactions: sepsis, HIT, and antiphospholipid syndrome. Hematology (Am Soc Hematol Educ Program). 2003;:497-519. [Medline]
- Warkentin TE, Cook DJ. Heparin, low molecular weight heparin, and heparin-induced thrombocytopenia in the ICU. Crit Care Clin. 2005 Jul;21(3):513-29. [Medline]
- Greinacher A. CLINICAL PRACTICE. Heparin-Induced Thrombocytopenia. N Engl J Med. 2015 Jul 16;373(3):252-61. [Medline]
Created: Sep 22, 2005.
Update: Sep 28, 2016.
