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.
I.
Evaluation of HIT
A. Patients should be evaluated via the Warkentin’s (modified) 4T’s scoring system1
4 T’s
Thrombocytopenia
2 points
platelet count fall >50%
1 point
platelet count fall 30-50%
Timing
CLEAR onset on days 5-10
platelet fall <1 day with
prior heparin exposure <30
days
Thrombosis
new confirmed thrombosis
skin necrosis at heparin
injection sites acute
systemic reaction following
heparin administration
none
UNCLEAR onset on days 510, OR > 10days
Platelet fall < 1day with
prior heparin exposure 30100 days
progressive thrombosis
non-necrotizing skin lesions
at heparin injection sites
unconfirmed thrombosis
other causes of
Thrombocytopenia
possible reason
No points
platelet count fall
<30%
Onset <day 4 without
previous exposure to
heparin
none
definite
UNMH risk strata: 0-3 = low, 4-5 = intermediate, 6-8 = high
i.
Low risk patients (score = 0-3)
a. Change to fondaparinux if possible (CrCl >30 ml/min, no epidural, etc)
b. If fondaparinux is not feasible, continue UFH or LMWH and continue to monitor platelets
ii. Moderate risk patients (score = 4-5)
a. If no evidence of thrombosis:
(a) Give fondaparinux treatment dose x 1 dose (will provide 24 hrs of anticoagulation while
awaiting heme consult)
b. Evidence of new thrombosis
(a) Start fondaparinux or bivalirudin
(b) Obtain baseline aPTT/INR, CBC, chem7
iii. High risk patients (score=6-8): start fondaparinux or bivalirudin
iv. For all moderate and high risk patients:
a. Discontinue all heparin, low molecular weight heparins, and warfarin products. (including flushes
and coated catheters)
b. Obtain Hematology/Oncology consult
c. Document adverse reaction to heparin in patient’s medical chart. (remove allergy if results are
negative)
d. Avoid any intramuscular injections
e. Order ELISA Heparin PF-4 test
f. Obtain baseline aPTT/INR, CBC, chem7
g.
B. Other possible HIT scoring schemes can be found in Appendix I
UNMH Inpatient Pharmacy Anticoagulation Services
Last updated July 2012
II. Laboratory evaluation of HIT
A. ELISA
i. Available at TriCore, run Monday, Wednesday and Friday afternoons with results available late
afternoon
ii. Test is very sensitive but non-specific – If positive, patient may have HIT but test cannot confirm
diagnosis.
B. SRA (Serotonin Release Assay)
i. Send out test, returns in approximately 7-10 days
ii. Test is very specific for HIT – if positive it will confirm diagnosis, if negative patient unlikely to have
HIT
III. Drug therapy for HIT
A. Do not wait for HIT panel confirmation prior to starting therapy
B. Orders for patients with suspected HIT should be entered under the HIT Powerplan
C. Fondaparinux
i. Considerations:
a. 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
b. Contraindicated if CrCl<30 ml/min (beyond 1x dose) or if spinal or epidural anesthesia
ii. 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
iii. Monitoring: Chem7 daily, CBC
D. Bivalirudin (***Only formulary direct thrombin inhibitor***)
i. Considerations:
a. Shortest elimination half-life of DTI’s
(a) Eliminated via blood proteases, thus less dependent on renal or hepatic elimination
(b) Mainly renally cleared, but can be dose adjusted
(i) t½ of bivalirudin increases as CrCl decreases
b. Least expensive DTI
c. If patient has had epidural/intrathecal/spinal procedure, consult with anesthesia prior to starting
anticoagulation
ii. Initial dosing:
a. CrCl >60 ml/min: 0.15 mg/kg/hr
b. CrCl 30-60 ml/min: 0.08 mg/kg/hr
c. CrCl < 30 ml/min: 0.05 mg/kg/hr
d. Dialysis: 0.02 mg/kg/hr
iii. Monitoring:
a. aPTT
(a) 2 hours after initiation or resumption of infusion
(b) 2 hours after any dose or rate change
(c) Once 2 consecutive aPTTs in range, change to qam aPTT
b. Labs: daily CBC, chem7
UNMH Inpatient Pharmacy Anticoagulation Services
Last updated July 2012
iv. Titration of dose:
aPTT (seconds)
<45
45-75
(1.5-2.5x mean
normal)
>75
Dose adjustment
Increase rate by 20%
Calculation
New rate= current rate x
1.2
AT GOAL= NO CHANGE
Hold infusion for 1 hour then restart at 50%
less than previous rate
New rate= current rate x
0.5
IV. Long-term anticoagulation
A. Warfarin should not be Initiated until platelets recover to baseline or after platelets are >150,000
B. Recommended treatment duration (not based on strong evidence, usually recommended by Hematology)
i. If no thrombotic event: 1-3 months
ii. If thrombotic event: 3-6 months
C. Collaborative practice with Hematology
i. Hematology should write at least 1 clinical note delineating duration and appropriateness of therapy
ii. 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
References:
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.
UNMH Inpatient Pharmacy Anticoagulation Services
Last updated July 2012
Appendix I: Other HIT Scoring Schemes:
I. HIT Expert Probability (HEP) Score3
A. Has not been prospectively validated and is not yet recommended for clinical use
Clinical Feature
Presentation
Score
Magnitude of fall in platelet count
< 30%
-1
(measured from peak to nadir since
30-50%
+1
heparin exposure)
>50%
+3
Timing of fall in platelet count
For patients in whom typical onset HIT is suspected:
Fall begins < 4 days after heparin exposure
-2
Fall begins 4 days after heparin exposure
+2
Fall begins 5-10 days after heparin exposure
+3
Fall begins 11-14 days after heparin exposure
+2
Fall begins > 14 days after heparin exposure
-1
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
+2
Fall begins > 48 hours after heparin exposure
-1
Nadir platelet count
≤ 20 × 109 L−1
-2
9 −1
> 20 × 10 L
+2
Thrombosis
For patients in whom typical onset HIT is suspected:
(select no more than one)
New VTE or ATE > 4 days after heparin exposure
+3
Progression of pre-existing VTE/ATE while
+2
receiving heparin
For patients in whom rapid onset HIT is suspected:
New VTE or ATE after heparin exposure
+3
Progression of pre-existing VTE /ATE while
+2
receiving heparin
Skin necrosis
Skin necrosis at subcutaneous heparin injection
+3
sites
Acute systemic reaction
Acute systemic reaction after intravenous heparin +2
bolus
Bleeding
Presence of bleeding, petechiae, or extensive
-1
bruising
Other causes of thrombocytopenia
Presence of a chronic thrombocytopenic disorder -1
(select all that apply)
Newly initiation non-heparin med known to cause -2
thrombocytopenia
Severe infection
-2
Severe DIC (fibrinogen < 100 mg/dL and D-dimer > -2
5 mcg/ml)
Indwelling intra-arterial device (IABP, VAD, ECMO) -2
Cardiopulmonary bypass within previous 96 hrs
-1
No other apparent cause
+3
VTE=venous thromboembolism; ATE=arterial thromboembolism; DIC=disseminated intravascular coagulation
A. Score interpretation:
i. Score may be interpreted 2 ways, however this will change the specificity and sensitivity.
ii. > 2 = positive for HIT; < 2 = negative for HIT
(Sensitivity 1.00 [0.56 – 1.00], Specificity 0.60 [0.45 - 0.75])
iii. > 5 = positive for HIT; < 5 = negative for HIT
(Sensitivity 0.86 [0.42 – 0.99], Specificity 0.88 [0.74-0.96])
UNMH Inpatient Pharmacy Anticoagulation Services
Last updated July 2012
II. Score for HIT in Cardiopulmonary Bypass2
Variables
Clinical Scenario
Platelet count time
Pattern A ((Platelet count begins to recover after CPB, but then
course
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
≥5 days
date
<5 days
CBP Duration
<118 minutes
≥118 minutes
A. Score interpretation:
i. < 2 = low probability of HIT
ii. > 2 = high probability of HIT
UNMH Inpatient Pharmacy Anticoagulation Services
Last updated July 2012
Points
2
1
2
0
1
0