Heparin induced thrombocytopenia Flashcards
Scoring system used for HIT + what’s included
4T Thrombocytopenia (Nadir >20K) Timing of platelet count fall Thrombosis No other cause for thrombocytopenia
Clinical features of Type 2 HIT
onset 5 to 10 days after heparin exposure + mean nadir platelet count 60k (those are only really 2 specific variables)
Management
Stop heparin → switch to therapeutically dosed argatroban, fondaparinux, or rivaroxaban (argatroban typically because of shorter duration) (ASH)
IF using warfarin → wait until platelet count recovers to > 150,000/µL, then start warfarin for 3-6 months
Bilateral Lower extremity US for DVT
Options + preferred AC for HIT
argatroban, fondaparinux, or rivaroxaban (argatroban typically because of shorter duration)
Tests used for HIT testing
1) ELISA for HIT antibody
2) Serotonin release assay -
How does serotonin release assay work
Functional assay – Measures ability of patient serum to activate test platelets in the presence of heparin
Type 1 HIT pathophys + clinical course + clinical relevance
- not antibody mediated, direct effect on platelets
- mild drop within a few days of starting heparin.
- The typical platelet count nadir is approximately 100,000/microL.
- not considered clinically significant, no thrombosis, and patients can be managed expectantly without discontinuation of heparin.
Type 2
Antibody mediated, more severe.
when do you send SGRA?
Intermediate probability of HIT
Management of type 1 HIT
- observe
- Don’t need to stop heparin.
why you can’t use warfarin instead
leads to a prothrombotic state
NPV of 4T’s score
100% for low score!
When to test for HIT
intermediate or high probability based off of 4T’s score
Problem with Elisa testing for HIT
- high false positive rate
Elisa interpretation — what OD confirms HIT? What is indeterminate?
- OD less than 0.6 = negative
- OD between 0.6 and 1.9 = indeterminate
*4T’s high probability and OD greater than 1.5 also confirms HIT - OD greater than 2.0 = HIT confirmed
OD = optical density
