Baseline CBC Should Be Obtained Before Starting Heparin Therapy
Yes, a complete blood count (CBC) should be obtained before starting heparin therapy to establish a baseline platelet count. 1 This is essential for monitoring potential heparin-induced thrombocytopenia (HIT), a serious complication that can lead to thrombosis and increased mortality.
Rationale for Baseline CBC Testing
- A baseline platelet count is necessary to detect relative changes that may indicate HIT development
- The American Society of Hematology specifically recommends obtaining a baseline platelet count before starting heparin therapy or as soon as possible after the first injection 1
- This baseline value serves as the reference point for detecting the ≥50% platelet count drop that is a key diagnostic criterion for HIT
Risk-Stratified Monitoring Approach
The frequency of subsequent platelet monitoring should be based on patient risk factors:
High-Risk Patients (>1% HIT risk)
- Surgical and trauma patients receiving unfractionated heparin (UFH)
- Monitor platelet counts every 2-3 days from day 4 to day 14 2, 1
Intermediate-Risk Patients (0.1-1% HIT risk)
- Medical and obstetric patients receiving UFH
- Patients receiving postoperative LMWH
- Monitor platelet counts every 2-4 days from day 4 to day 14 2, 1
Low-Risk Patients (<0.1% HIT risk)
Special Considerations
Recent heparin exposure: For patients who received heparin within the previous 100 days, obtain a baseline platelet count and a repeat count 24 hours after starting heparin 2, 1, 3
- These patients may have circulating HIT antibodies that can cause rapid-onset HIT with re-exposure 4
Acute reactions: For patients who develop acute inflammatory reactions (fever, chills) or cardiorespiratory symptoms within 30 minutes of IV heparin bolus, perform an immediate platelet count 2
Monitoring Parameters
The complete baseline laboratory assessment should include:
- Complete blood count with platelet count
- Activated partial thromboplastin time (aPTT)
- Prothrombin time (PT)/INR if patient will transition to warfarin
- Serum creatinine and creatinine clearance 1
Warning Signs Requiring Immediate Action
Monitor for these key indicators that should prompt immediate HIT evaluation:
- Platelet count drop ≥50% from baseline
- New thrombotic events while on heparin
- Skin necrosis or unusual reactions after heparin injection 1
Clinical Pitfalls to Avoid
- Don't start warfarin in patients with suspected HIT until platelet count has substantially recovered (usually to at least 150 × 10^9/L) 5
- Don't delay testing if HIT is suspected - immediately discontinue all heparin products and initiate alternative anticoagulation 1
- Don't ignore mild thrombocytopenia - even moderate drops in platelet count can indicate HIT, with a median nadir of approximately 50-60 × 10^9/L 6
By obtaining a baseline CBC before starting heparin therapy and following appropriate monitoring protocols, clinicians can identify HIT early and prevent potentially life-threatening thrombotic complications.