Dr. Weber treated us to a fun and informative case where a patient who was POD5 from CABG was readmitted and developed heparin-induced thrombocytopenia.
What is Heparin-induced thrombocytopenia (HIT)?
HIT is a specific type of drug-induced thrombocytopenia. In HIT, antibodies form against an antigenic complex between platelet factor 4 (PF4) and heparin. Antibodies directed against this complex then can activate platelets via their Fc receptors. This process results in thrombocytopenia but this is also why some patients can present with thrombosis.
Who gets HIT?
Risk factors include the following:
-Heparin treatment for more than 4 days
-Recent Surgery
-Treatment with unfractionated instead of low-molecular-weight heparin
Uh oh... my NSTEMI patient has a falling platelet count.
First, use the 4T score to determine the probability of HIT.
If your score is 0 to 3, do nothing. It’s almost certainly not HIT. If your score is higher, you should send testing.
Diagnostic testing involves both serologic testing for anti-heparin/PF4 antibodies and functional assays to determine platelet activation, of which the serotonin release assay is the gold standard.
Because testing takes a while and this can be deadly, you should presumptively treat while awaiting the test.
1. Stop all heparin products- don’t forget flushes, heparin locks, and lovenox.
2. Start therapy with argatroban therapy.
3. Order diagnostic testing.
Other pearls:
Baseline Doppler ultrasound studies of all four extremities should be obtained: the risk of thrombosis in HIT is more than 30%.
Warfarin can be used for treatment but it cannot be started until the platelet count normalizes because of the risk of developing warfarin skin necrosis.
Do NOT give platelets unless critical.
Anticoagulation should be continued at least until the platelet count is greater than 150,000/µL in patients without thrombosis.
Patients with thrombosis should complete the course of anticoagulation needed to treat their clot.
References:
MKSAP 17
Cuker A, Gimotty PA, Crowther MA, Warkentin TE. Predictive value of the 4Ts scoring system for heparin-induced thrombocytopenia: a systematic review and meta-analysis. Blood. 2012 Nov 15;120(20):4160-7.
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