Classification: Type 1 vs. Type 2
|
Type 1 |
Type 2 |
|
|---|---|---|
|
Frequency |
10-20% |
1-3% |
|
Timing |
1-4 days |
5-10 days (and even longer) |
|
Nadir of platelet count |
100,000 |
30-55,000 |
|
Antibody mediated |
No |
Yes |
|
Thromboembolic events |
None |
30-80% |
|
Hemorrhagic events |
None |
Rarely |
|
Management |
Observe |
Discontinue heparin and start alternate anticoagulant. |
Evaluate the pre-test probability of HIT: unfortunately, the laboratory tests to diagnose HIT take at least a few days to come back. Therefore, use the following clinical scoring system (4-T score) to determine the pre-test probability of HIT and the appropriate management plan. Remember to periodically re-assess, as new information can change pre-test probability (e.g. positive blood cultures).
|
Clinical Factor |
2 points |
1 point |
0 points |
|---|---|---|---|
|
Thrombocytopenia |
Nadir 20-100, or >50% platelet fall |
Nadir 10-19 or 30-50% platelet fall |
Nadir <10, or <30% platelet fall |
|
Timing of onset of platelet fall |
Day 5-10, or ≤ day 1 with recent heparin (past 30 days) |
> day 10 or timing unclear (but fits with HIT) |
≤ day 1 (no recent heparin) |
|
Thrombosis or other sequelae |
Proven thrombosis, skin necrosis, or acute systemic reaction following bolus of heparin IV |
Progressive, recurrent, or silent thrombosis; erythematous skin lesions |
None |
|
Other cause of platelet fall |
None evident |
Possible |
Definite |
Initial Management
- Based on the total pre-test probability score, come up with a management plan (total score 0 to 8):
- Score 0-3: continue heparin; no need for further testing.
- Score 4-5: physician judgment; consider laboratory testing.
- Score 6-8:
- Perform laboratory testing for confirmation (see below).
- Stop all heparin, including heparin flushes and heparin-coated catheters. Give alternative, non-heparin anticoagulant (direct thrombin inhibitor or non-heparin factor Xa inhibitor).
- Avoid warfarin until platelet count >100,000/μL. Warfarin starting dose should be low and therapy should be overlapped with a direct thrombin inhibitor for a minimum of 5 days.
Laboratory Diagnosis
- Based on your pre-test probability score, seek further laboratory testing starting with a platelet factor 4 antibody assay (“HIT” antibodies). Proceed as follows:
|
Pretest Score |
PF4Ab NEGATIVE |
PF4Ab POSITIVE |
|---|---|---|
|
6-8 |
Send Serotonin Release Assay |
STOP. HIT confirmed |
|
4-5 or recent CABG |
STOP. No HIT |
Send Serotonin Release Assay |
|
0-3 |
No testing indicated |
No testing indicated |
Treatment
- Includes stopping all heparin products (including heparin flushes and heparin-coated catheters) and instituting alternate anticoagulation, to prevent thrombotic complications. Choices include bivalirudin, lepirudin, or argatroban (direct thrombin inhibitors).
- With liver disease best choices are lepirudin, danaparoid, or fondaparinux and with renal disease can use argatroban or lower doses of lepirudin. See section Hematology/Oncology: IV Direct Thrombin Inhibitors.
Key Points
- Type I is a nonimmune phenomenon and limited while Type II is an antibody-mediated disorder including HIT and requires treatment.
- If HIT is suspected, assess the pretest probability to guide management.
- Complications include arterial or venous thromboses; often occur at sites of pre-existing pathology.
Alving BM. How I treat heparin-induced thrombocytopenia and thrombosis. Blood 2003;101:31-37.
Rice L, Attisha WK, Drexler A, et al. Delayed-onset heparin-induced thrombocytopenia. Ann Intern Med 2002;136:210-215.
UCSF Comprehensive Hemostasis and Antithrombotic Service (CHAS) guidelines, 2004