Algorithm for evaluating and treating suspected HIT

HIT: heparin-induced thrombocytopenia; PLT: platelet count; DIC: disseminated intravascular coagulation; ELISA: enzyme-linked immunosorbent assay; OD: optical density; SRA: serotonin release assay; HIPA: heparin-induced platelet aggregation.
* There may be extremely rare cases in which an individual with a low probability 4 Ts score has HIT.
¶ Warfarin is a reasonable choice for anticoagulation in HIT, but it must not be started until the individual is stably anticoagulated with a non-heparin agent and their platelet count has recovered; initiation of warfarin creates a transient prothrombotic state.

• For patients receiving warfarin who develop HIT or who have an intermediate or high probability 4 Ts score and are awaiting the results of definitive laboratory testing, warfarin should be reversed with vitamin K (and no additional warfarin should be given).
• Refer to UpToDate for details on the timing of warfarin reversal relative to the initiation of the non-heparin anticoagulant.

Δ Options for initial anticoagulation include:

• Parenteral agents such as argatroban, bivalirudin, danaparoid, fondaparinux.
• A direct oral anticoagulant (dabigatran, apixaban, rivaroxaban, edoxaban).

Refer to UpToDate for important considerations related to administration route, half-life, use in renal and hepatic failure, and monitoring. Rarely, an anticoagulant may be omitted in an individual at high risk of bleeding. However, thrombocytopenia is not a contraindication to anticoagulation as it is expected to resolve rapidly upon heparin discontinuation.
◊ In most centers, an immunoassay (eg, ELISA) is ordered first because it is performed in-house and has a faster turnaround time. Some centers may follow a different protocol (eg, initial SRA or HIPA). Clinicians should be familiar with the practices of their institution.