What is the indication for low‑dose aspirin in patients with polycythemia (especially polycythemia vera) who have no contraindications to antiplatelet therapy?

Indication for Aspirin in Polycythemia Vera

All patients with polycythemia vera (PV) should receive low-dose aspirin (81-100 mg daily) unless they have contraindications to antiplatelet therapy 1, 2, 3.

Primary Indication and Evidence Base

Low-dose aspirin is indicated for thromboprophylaxis in PV patients. The landmark ECLAP trial demonstrated that aspirin 100 mg daily significantly reduced the combined endpoint of nonfatal myocardial infarction, nonfatal stroke, pulmonary embolism, major venous thrombosis, or cardiovascular death (relative risk 0.40,95% CI 0.18-0.91, P=0.03) without significantly increasing major bleeding risk 4. This applies to patients with no clear indication or contraindication to aspirin therapy.

Risk Stratification and Treatment Algorithm

All Risk Categories

• Low-dose aspirin (81-100 mg daily) is recommended for both low-risk and high-risk PV patients 2, 3
• Combine with therapeutic phlebotomy to maintain hematocrit <45% 2, 3

High-Risk Patients (age ≥60 years OR prior thrombosis)

• Add cytoreductive therapy (hydroxyurea preferred) to aspirin and phlebotomy 2, 3

Low-Risk Patients

• Aspirin and phlebotomy alone are typically sufficient 2, 3

Specific Clinical Scenarios

Microvascular symptoms (erythromelalgia, visual disturbances, transient neurological symptoms) are highly responsive to aspirin and represent a strong indication for treatment 5, 6.

Thrombosis prevention: Aspirin addresses both arterial and venous thrombotic risk, which affects 16% (arterial) and 7% (venous) of patients at or before diagnosis 3.

Critical Contraindications to Assess

Before prescribing aspirin, evaluate for:

• Acquired von Willebrand disease: Particularly in patients with extreme thrombocytosis (platelet count ≥1000 × 10⁹/L), which increases bleeding risk 2, 3
• Active bleeding or history of major bleeding 7
• Severe allergic reactions to aspirin (hives, facial swelling, asthma) 7
• Active peptic ulcer disease or gastrointestinal bleeding 7
• Age >60 years with prior ulcers or bleeding problems requires careful risk-benefit assessment 7

Important Caveats

Pregnancy: Aspirin should be avoided, especially in the last trimester, unless specifically directed by a physician due to risks to the fetus and delivery complications 7.

Bleeding risk monitoring: While the ECLAP trial showed no significant increase in major bleeding (relative risk 1.62,95% CI 0.27-9.71), minor bleeding showed a non-significant trend toward increase 4, 8. Monitor for bleeding symptoms, particularly mucocutaneous and gastrointestinal bleeding.

Hematocrit control is essential: Aspirin efficacy is optimized when hematocrit is maintained <45% through phlebotomy, as demonstrated in the CYTO-PV trial 1, 2.

Essential Thrombocythemia Context

The evidence for aspirin in essential thrombocythemia (ET) is less robust than in PV, being largely extrapolated from the ECLAP study in PV patients 2. Guidelines suggest aspirin "could be considered" for low-risk ET patients, but the recommendation is weaker and requires careful assessment of bleeding risk, particularly in patients with acquired von Willebrand disease 2.