Dalteparin Discontinuation Based on Platelet Count
Dalteparin should be immediately discontinued if the platelet count falls below 100,000/mm³ or drops by 50% or more from baseline, particularly between days 4-14 of therapy, as this raises concern for heparin-induced thrombocytopenia (HIT). 1, 2, 3
Critical Platelet Thresholds for Action
Stop dalteparin immediately when:
- Platelet count falls below 100,000/mm³ 1, 2, 4
- Platelet count decreases by ≥50% from baseline, even if still above 100,000/mm³ 3, 5
- New thrombosis develops during therapy, regardless of platelet count 1, 2
- Unexplained clinical deterioration occurs (recurrent thrombosis, skin necrosis, acute systemic reactions) 6, 3
Monitoring Requirements for Dalteparin
For patients at >1% risk of HIT:
- Obtain baseline platelet count before starting dalteparin 1, 3
- Monitor platelet counts every 2-3 days from day 4 to day 14 of therapy 1, 6
- Continue monitoring until dalteparin is discontinued 1
For patients with recent heparin exposure (within 100 days):
- Obtain baseline platelet count and repeat at 24 hours after starting dalteparin 3
- Monitor every 2-3 days from day 4-14, as rapid-onset HIT can occur due to preformed antibodies 1, 7
For patients at <1% risk of HIT:
- Routine platelet monitoring is not required 1
Immediate Management After Stopping Dalteparin
Once HIT is suspected and dalteparin stopped:
Do NOT wait for laboratory confirmation - the thrombotic risk is too high 6, 8
Initiate alternative anticoagulation immediately with one of the following 1, 6:
Avoid warfarin until platelet count recovers to ≥150,000/mm³ to prevent venous limb gangrene 1, 8, 7
Do NOT give platelet transfusions unless active bleeding or high-risk invasive procedure, as they paradoxically worsen thrombosis 1, 8
Critical Timing Considerations
The typical window for HIT development is days 5-14 after starting dalteparin 1. However, important exceptions include:
- Rapid-onset HIT (within 24 hours to 5 days) occurs in patients with heparin exposure in the preceding 3 months due to preformed antibodies 1, 7
- Delayed-onset HIT can occur up to several weeks after stopping dalteparin 2, 7
Common Pitfalls to Avoid
Never continue dalteparin while awaiting HIT antibody test results - the mortality and morbidity from thrombotic complications are too high 6, 8. The median platelet nadir in HIT is 50,000-60,000/mm³, but severe thrombocytopenia with disseminated intravascular coagulation can occur 7.
Do not switch to low-molecular-weight heparin (LMWH) or unfractionated heparin as alternatives, as cross-reactivity occurs in the majority of HIT cases 1, 3. All heparin products, including heparin flushes for IV lines, must be discontinued 1, 2.
Avoid starting warfarin prematurely (before platelet recovery to ≥150,000/mm³), as this increases the risk of venous limb gangrene and skin necrosis 1, 8. If warfarin was already started when HIT is diagnosed, administer vitamin K 1, 7.