What labs should I order before starting heparin (unfractionated heparin) subcutaneously?

Laboratory Tests Required Before Starting Subcutaneous Heparin

Before starting subcutaneous unfractionated heparin therapy, a baseline complete blood count (CBC) with platelet count and activated partial thromboplastin time (aPTT) should be obtained. 1

Essential Pre-Heparin Laboratory Tests

• Complete Blood Count (CBC)

  • Hemoglobin and hematocrit (to establish baseline for monitoring bleeding risk)
  • Platelet count (critical for HIT risk assessment)

• Coagulation Profile

  • Activated Partial Thromboplastin Time (aPTT)
  • Prothrombin Time (PT)/International Normalized Ratio (INR) if patient is on or will transition to warfarin

• Renal Function

  • Serum creatinine and creatinine clearance (especially important if renal dysfunction is suspected)

Risk Assessment for Heparin-Induced Thrombocytopenia (HIT)

The American Society of Hematology (ASH) recommends different monitoring approaches based on HIT risk 2:

• Low-risk patients (<0.1% risk of HIT): No routine platelet monitoring needed
• Intermediate-risk patients (0.1%-1.0% risk of HIT): Monitor platelet count every 2-3 days from day 4 to day 14
• High-risk patients (>1.0% risk of HIT): Monitor platelet count at least every other day from day 4 to day 14

Monitoring During Heparin Therapy

After initiating subcutaneous heparin:

• Monitor hemoglobin, hematocrit, and platelet count every 2-3 days up to at least day 14, then every 2 weeks thereafter 2
• For subcutaneous heparin, tests for adequacy of dosage are best performed on samples drawn 4-6 hours after injection 1

Special Considerations

• Previous Heparin Exposure: If the patient has received heparin in the previous 30 days, platelet count monitoring should begin on day 0 (the day heparin is initiated) 2

• Contraindications to Check For:

  • Active major bleeding (>2 units transfused in 24h)
  • Severe thrombocytopenia (platelets <50,000/mcL)
  • Recent spinal anesthesia/lumbar puncture
  • Intracranial or spinal lesions at high risk for bleeding 2

Common Pitfalls to Avoid

1. Failure to obtain baseline labs: Always obtain baseline values before starting therapy to allow for meaningful comparison during treatment.

2. Overlooking HIT risk assessment: HIT is a serious complication with significant morbidity and mortality. Risk stratification is essential for determining monitoring frequency.

3. Inadequate monitoring schedule: Following the recommended monitoring schedule based on risk stratification is crucial for early detection of complications.

4. Missing renal function assessment: Renal dysfunction may affect heparin clearance and increase bleeding risk, making baseline assessment important.

By following these laboratory testing guidelines before initiating subcutaneous heparin therapy, you can establish appropriate baselines, identify contraindications, and develop a monitoring plan that optimizes efficacy while minimizing the risk of adverse events.