Heparin-Induced Thrombocytopenia Management (ASH 2018)

Algorithm Steps

1. ▶

   Start

   Suspected HIT

   Platelet count drop or thrombosis in patient on heparin

   1. ◆

      Decision

      Appropriate Timing?

      Typical onset 5-10 days after heparin start (or sooner if prior exposure)

      • Typical onset: Day 5-10 of heparin exposure
      • Rapid onset: <24h if heparin in past 100 days
      • Delayed onset: Days after stopping heparin (rare)
      1. ●

         Action

         Calculate 4Ts Score

         Clinical probability assessment

         • Thrombocytopenia: >50% fall or nadir 20-100k (2), 30-50% fall or nadir 10-19k (1), <30% fall or nadir <10k (0)
         • Timing: Day 5-10 or ≤1d if recent heparin (2), after day 10 or unclear (1), ≤4d without recent (0)
         • Thrombosis: New thrombosis, skin necrosis, anaphylactoid (2), progressive/recurrent (1), none (0)
         • Other causes: None apparent (2), possible (1), definite (0)
         1. ◆

            Decision

            4Ts Score Result

            Risk stratification

            1. ●

               Action

               Score 0-3: Low Probability

               HIT unlikely (<5%)

               • Continue heparin if indicated
               • Seek other causes of thrombocytopenia
               • No HIT testing typically needed
               • Reassess if clinical picture changes
               1. ✓

                  Outcome

                  HIT Managed

                  Appropriate anticoagulation, platelet recovery monitoring

            2. ●

               Action

               Score 4-5: Intermediate

               HIT possible (~14%)

               • STOP all heparin (including flushes, coated catheters)
               • Start alternative anticoagulant
               • Send PF4/heparin immunoassay
               • Await results before confirming/excluding
               1. ⚠

                  Warning

                  STOP ALL HEPARIN

                  Including flushes, coated catheters, LMWH

                  1. ●

                     Action

                     Start Alternative Anticoagulant

                     Therapeutic dosing if thrombosis or high probability

                     • Argatroban: 2 mcg/kg/min IV (reduce in hepatic dysfunction)
                     • Bivalirudin: 0.15-0.2 mg/kg/hr IV (adjust for renal)
                     • Fondaparinux: 7.5mg SQ daily (off-label, weight-based)
                     • DOACs: After platelet recovery, can transition
                     • Avoid warfarin until platelets >150k
                     1. ◆

                        Decision

                        Laboratory Results

                        Immunoassay and/or functional assay

                        1. ●

                           Action

                           HIT Confirmed

                           Positive immunoassay + functional assay or high-titer immunoassay

                           • Continue alternative anticoagulation
                           • Duration: Minimum 4 weeks (no thrombosis) or 3 months (with thrombosis)
                           • Transition to warfarin after plt >150k (overlap 5+ days)
                           • DOACs increasingly used post-acute phase
                           • Document HIT allergy in medical record
                        2. ●

                           Action

                           HIT Excluded

                           Negative immunoassay or negative functional assay

                           • Can resume heparin if needed
                           • Seek other causes of thrombocytopenia
                           • Consider functional assay if immunoassay indeterminate
            3. ⚠

               Warning

               Score 6-8: High Probability

               HIT likely (~64%)

               • STOP all heparin immediately
               • Start alternative anticoagulant at therapeutic dose
               • Send PF4/heparin immunoassay + functional assay (SRA)