COW Week 4 Answer

This patient should have been started on argatroban 2 days ago when HIT was suspected and should stay in the hospital for minimum 2 weeks on an argatroban drip. Fonadaprinux can be used off-label for outpatient management but this is not FDA approved. Coumadin is not appropriate as HIT is a very hypercoagulable state requiring a “true” anticoagulant. Coumadin does not inhibit activated clotting factors and has also been associated with a purpura fulminans kind of syndrome in this setting. Up to 50% of patients with HIT develop thrombosis.

Words of Wisdom from Dr. Rosove:

This patient has heparin induced thrombocytopenia (HIT). HIT develops anywhere from day 4 to 14 of de novo therapy. It takes that long for IgG antibodies to the heparin-platelet factor 4 complex to develop. Thrombocytopenia can occur earlier than day 4, even immediately, upon exposure to unfractionated heparin (UFH) if there has been a recent exposure to any glycosaminoglycan anticoagulant, GAG, (UFH, LMWH, or fondaparinux) such that antibodies are already present. This patient was exposed to heparin recently which is why her platelets dropped so quickly.

HIT patients must be anticoagulated for a minimum of two weeks (3 months per Board Review), even if there is full recovery of the platelet count, no evident thrombosis, and no need for longer-term anticoagulation. By two weeks, nearly all of the acute risk has passed. If there is evidence of thrombosis then one must be anti-coagulated for 3-6months. The only FDA-approved anticoagulants for HIT are argatroban, bivalirudin, and lepirudin (the first two are on our formulary), but these are IV infusions, thus requiring inpatient care. Therefore fondaparinux SQ is often given off-label to allow outpatient management. Fondaprinux may perpetuate antibody formation but is virtually incapable of causing HIT. Rivaroxaban or dabigatran could also serve in the same capacity since they are not GAGs, but neither have been tested and thus should not be used at this time.

HIT is a preventable problem. By far it occurs more frequently with UFH than LMWH, and HIT due to fondaparinux is practically reportable. Therefore, whenever there is a reasonable choice of which anticoagulant to use, UFH is best avoided altogether. In the case of unstable angina and percutaneous coronary interventions, there are legitimate alternatives to UFH.

A positive HAPA, no matter how strongly positive, only permits a diagnosis of HIT, it does not make a diagnosis since the majority of patients who are antibody positive do not have HIT. However, the negative predictive value of HAPA is nearly perfect.

ACCP 2012 Guidelines: HIT 

HIT Clinical Review