HIT Flashcards
HIT type 1
see acute drop in platelets within 48 hours and mild transient effect of heparin on platelets.
Plts rarely drop less than <100K and recovers spontaneously regardless of stopping heparin or continuing it.
normalization is quick and not tx is needed.
is HIT type 1 clinically significant?
no, because not associated with VTE
heparin should not be discontinued with HIT type 1
HIT type 2 is
clinically relevant and an immune mediated disorder that causes platelet aggregation and thrombosis and this disorder results in thrombocytopenia 5 to 10 days after heparin exposure
4 t score is based of probability for HIT type 2
worse things would be degree of thrombocytopenia (50% or nadir <20K)
timing of drop (onset 5-10 days or <1 day if prior heparin exposure in last 30 days)
thrombosis (confirmed new thrombosis, skin necrosis or reaction after IV heparin bolus)
AND most importantly no apparent cause for these symptoms
which antibiotic can cause thrombocytopenia?
ceftriaxone and zosyn
When does HIT 2 see changes in thrombocytopenia
5-14 days after heparin therapy or within 24 hrs of heparin re exposure (rapid onset HIT)
highest risk factors for HIT 2 is
type of heparin exposure (highest risk is unfractionated heparin)
duration of tx
gender (higher in women)
trauma severity (higher risk in surgical pts)
When to suspect HIT2?
platelets decrease >50% from baseline 5-14 days after starting heparin and new onset unexplained thrombocytopenia and thrombosis after heparin treatment
4T score for HIT evaluation stand for
thrombocytopenia
timing
thrombosis
and oTher causes
Diagnosis of HIT 2 is confirmed with
serotonin release assays (preferred) and heparin induced platelet aggregation assays and solid phase immunoassays with ELISA for heparin PF4 complexes.
Management of suspected HIT2
all forms of heparin must be stopped (including low molecular weight heparin like enoxaparin)
Should get alternate form of rapid acting AC as they are high risk for thrombosis like argatroban, bivalirudin or fondaparinux
Clinical observation without alternate AC therapy is only recommended in
high bleeding risk pts. HIT increases risk for thrombosis and compression stockings do not treat acute thrombus or effectively prevent future ones.
After HIT2 is done what should be done in terms of AC?
transition AC into a vitamin K antagonist or alternate AC for 3 months.
initial treatment with warfarin is usually contraindicated as rapidly dropping protein C can cause a prothrombotic state.
Usually hold off on warfarin until non heparin anticoagulant is started and recovers a platelet count of 150K
When to start warfarin after a suspected HIT pt?
Usually hold off on warfarin until non heparin anticoagulant is started and recovers a platelet count of 150K
initial treatment with warfarin is usually contraindicated as rapidly dropping protein C can cause a prothrombotic state.
what is delayed onset HIT
immune mediated due to high titer antibodies against heparin PF4 copmlexes in the absence of circulating heparin.
arise 5-19 dyas after heparin cessation and so most pts present as outpatinet
