Heparin Induced Thrombocytopenia (hit) Guideline

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Heparin Induced Thrombocytopenia (HIT) Guideline

This document is intended as a guideline only and should not replace sound clinical judgment

Please refer providers to the HIT Powerplan for questions regarding HIT and HIT antibodies as it will walk the provider through the 4T scoring and HIT treatment options.
Also, the Anticoagulation Pharmacist can serve as a resource and should be notified of potential HIT patients via Quantifi and/or a phone call.

  1. Evaluation of HIT

    1. Patients should be evaluated via the Warkentin’s (modified) 4T’s scoring system1

4 T’s

2 points

1 point

No points


platelet count fall >50%

platelet count fall 30-50%

platelet count fall <30%


CLEAR onset on days 5-10

platelet fall <1 day with prior heparin exposure <30 days

UNCLEAR onset on days 5-10, OR > 10days

Platelet fall < 1day with prior heparin exposure 30-100 days



new confirmed thrombosis

skin necrosis at heparin injection sites acute systemic reaction following heparin administration

progressive thrombosis

non-necrotizing skin lesions at heparin injection sites

unconfirmed thrombosis


other causes of Thrombocytopenia


possible reason


UNMH risk strata: 0-3 = low, 4-5 = intermediate, 6-8 = high

      1. Low risk patients (score = 0-3)

        1. Change to fondaparinux if possible (CrCl >30 ml/min, no epidural, etc)

        2. If fondaparinux is not feasible, continue UFH or LMWH and continue to monitor platelets

      2. Moderate risk patients (score = 4-5)

        1. If no evidence of thrombosis:

          1. Give fondaparinux treatment dose x 1 dose (will provide 24 hrs of anticoagulation while awaiting heme consult)

        2. Evidence of new thrombosis

          1. Start fondaparinux or bivalirudin

          2. Obtain baseline aPTT/INR, CBC, chem7

      3. High risk patients (score=6-8): start fondaparinux or bivalirudin

      4. For all moderate and high risk patients:

        1. Discontinue all heparin, low molecular weight heparins, and warfarin products. (including flushes and coated catheters)

        2. Obtain Hematology/Oncology consult

        3. Document adverse reaction to heparin in patient’s medical chart. (remove allergy if results are negative)

        4. Avoid any intramuscular injections

        5. Order ELISA Heparin PF-4 test

        6. Obtain baseline aPTT/INR, CBC, chem7

    1. Other possible HIT scoring schemes can be found in Appendix I

  1. Laboratory evaluation of HIT

    1. ELISA

      1. Available at TriCore, run Monday, Wednesday and Friday afternoons with results available late afternoon

      2. Test is very sensitive but non-specific – If positive, patient may have HIT but test cannot confirm diagnosis.

    2. SRA (Serotonin Release Assay)

      1. Send out test, returns in approximately 7-10 days

      2. Test is very specific for HIT – if positive it will confirm diagnosis, if negative patient unlikely to have HIT

  1. Drug therapy for HIT

    1. Do not wait for HIT panel confirmation prior to starting therapy

    2. Orders for patients with suspected HIT should be entered under the HIT Powerplan

    3. Fondaparinux

      1. Considerations:

        1. Will not break down active clots, therefore patients with active clots may need to be switched to bivalirudin. This determination should be made by hematology

        2. Contraindicated if CrCl<30 ml/min (beyond 1x dose) or if spinal or epidural anesthesia

      2. Treatment dosing: ≤ 50 kg use 5 mg SubQ daily

75-100 kg use 7.5 mg SubQ daily

≥ 100 kg use 10 mg SubQ daily

Prophylactic dosing: 2.5 mg SubQ daily

      1. Monitoring: Chem7 daily, CBC

    1. Bivalirudin (***Only formulary direct thrombin inhibitor***)

      1. Considerations:

        1. Shortest elimination half-life of DTI’s

          1. Eliminated via blood proteases, thus less dependent on renal or hepatic elimination

          2. Mainly renally cleared, but can be dose adjusted

            1. t½ of bivalirudin increases as CrCl decreases

        2. Least expensive DTI

        3. If patient has had epidural/intrathecal/spinal procedure, consult with anesthesia prior to starting anticoagulation

      2. Initial dosing:

        1. CrCl >60 ml/min: 0.15 mg/kg/hr

        2. CrCl 30-60 ml/min: 0.08 mg/kg/hr

        3. CrCl < 30 ml/min: 0.05 mg/kg/hr

        4. Dialysis: 0.02 mg/kg/hr

      3. Monitoring:

        1. aPTT

          1. 2 hours after initiation or resumption of infusion

          2. 2 hours after any dose or rate change

          3. Once 2 consecutive aPTTs in range, change to qam aPTT

        2. Labs: daily CBC, chem7

      1. Titration of dose:

        aPTT (seconds)

        Dose adjustment



        Increase rate by 20%

        New rate= current rate x 1.2


        (1.5-2.5x mean normal)



        Hold infusion for 1 hour then restart at 50% less than previous rate

        New rate= current rate x 0.5

  1. Long-term anticoagulation

    1. Warfarin should not be Initiated until platelets recover to baseline or after platelets are >150,000

    2. Recommended treatment duration (not based on strong evidence, usually recommended by Hematology)

      1. If no thrombotic event: 1-3 months

      2. If thrombotic event: 3-6 months

    3. Collaborative practice with Hematology

      1. Hematology should write at least 1 clinical note delineating duration and appropriateness of therapy

      2. Thereafter, they may choose to sign off and turn dosing of medications over the anticoagulation service.

Please direct providers to use the HIT Powerplan in Powerchart. Educational inservice may be required.

Document originated by: Pree Sarangarm, PharmD

Reviewed by: David Garcia, MD; Richard D’Angio, PharmD; Allison Burnett, PharmD


  1. Lo GK, Juhl D, Warkentin TE, Sigouin CS, Eichler P, Greinacher A. Evaluation of pretest clinical score (4 T’s) for the diagnosis of heparin-induced thrombocytopenia in two clinical settings. J Thromb Haemost 2006; 4: 759–65.

  2. Lillo-Le Louët A, Boutouyrie P, Alhenc-Gelas M, Le Beller C, Gautier I, Aiach M, Lasne D. Diagnostic score for heparin-induced thrombocytopenia after cardiopulmonary bypass. J Thromb Haemost 2004; 2: 1882–8.

  3. Cuker A, Arepally G, Crowther MA, Rice L, Datko F, Hook K, Propert KJ, Kuter DJ, Ortel TL, Konkle BA, Cines DB. The HIT Expert Probability (HEP): Score: a novel pre-test probability model for heparin-induced thrombocytopenia based on broad expert opinion. J Thromb Haemost 2010; 8:2642-50.

Appendix I: Other HIT Scoring Schemes:

  1. HIT Expert Probability (HEP) Score3

    1. Has not been prospectively validated and is not yet recommended for clinical use

Clinical Feature



Magnitude of fall in platelet count (measured from peak to nadir since heparin exposure)

< 30%






Timing of fall in platelet count

For patients in whom typical onset HIT is suspected:

Fall begins < 4 days after heparin exposure


Fall begins 4 days after heparin exposure


Fall begins 5-10 days after heparin exposure


Fall begins 11-14 days after heparin exposure


Fall begins > 14 days after heparin exposure


For patients with previous heparin exposure in the last 100 days in whom rapid onset HIT is suspected:

Fall begins < 48 hours after heparin exposure


Fall begins > 48 hours after heparin exposure


Nadir platelet count

≤ 20 × 109 L−1


> 20 × 109 L−1


(select no more than one)

For patients in whom typical onset HIT is suspected:

New VTE or ATE > 4 days after heparin exposure


Progression of pre-existing VTE/ATE while receiving heparin


For patients in whom rapid onset HIT is suspected:

New VTE or ATE after heparin exposure


Progression of pre-existing VTE /ATE while receiving heparin


Skin necrosis

Skin necrosis at subcutaneous heparin injection sites


Acute systemic reaction

Acute systemic reaction after intravenous heparin bolus



Presence of bleeding, petechiae, or extensive bruising


Other causes of thrombocytopenia (select all that apply)

Presence of a chronic thrombocytopenic disorder


Newly initiation non-heparin med known to cause thrombocytopenia


Severe infection


Severe DIC (fibrinogen < 100 mg/dL and D-dimer > 5 mcg/ml)


Indwelling intra-arterial device (IABP, VAD, ECMO)


Cardiopulmonary bypass within previous 96 hrs


No other apparent cause


VTE=venous thromboembolism; ATE=arterial thromboembolism; DIC=disseminated intravascular coagulation

    1. Score interpretation:

      1. Score may be interpreted 2 ways, however this will change the specificity and sensitivity.

      2. > 2 = positive for HIT; < 2 = negative for HIT
        (Sensitivity 1.00 [0.56 – 1.00], Specificity 0.60 [0.45 - 0.75])

      3. > 5 = positive for HIT; < 5 = negative for HIT
        (Sensitivity 0.86 [0.42 – 0.99], Specificity 0.88 [0.74-0.96])

  1. Score for HIT in Cardiopulmonary Bypass2


    Clinical Scenario


    Platelet count time course

    Pattern A ((Platelet count begins to recover after CPB, but then begins to fall again > 4 days after CPB)


    Pattern B (Thrombocytopenia occurs immediately after CPB and persists for > 4 days without recovery)


    Time from CPB to index date

    ≥5 days


    <5 days


    CBP Duration

    <118 minutes


    ≥118 minutes


    1. Score interpretation:

      1. < 2 = low probability of HIT

      2. > 2 = high probability of HIT

UNMH Inpatient Pharmacy Anticoagulation Services Last updated July 2012

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