What is the management for elevated hematocrit (hyper viscosity) in smokers?

Management of Elevated Hematocrit in Smokers

The primary intervention for elevated hematocrit (hyperviscosity) in smokers is complete smoking cessation, which can lead to normalization of hematocrit within days to weeks. For patients with significantly elevated hematocrit (>65%) or symptomatic hyperviscosity, therapeutic phlebotomy should be considered, targeting a hematocrit below 45% to reduce thrombotic risk 1.

Pathophysiology

• Smoking causes elevated hematocrit through:
  • Carbon monoxide exposure, which binds to hemoglobin with 200-250 times greater affinity than oxygen 1
  • Smokers typically have carboxyhemoglobin (COHb) levels of 3-5%, with levels rising approximately 2.5% per pack smoked daily 1
  • Heavy smokers can have COHb levels exceeding 10%, especially with underlying lung disease 1
  • Smoking creates a relatively hypercoagulable state with increased hematocrit and fibrinogen levels 2

Diagnostic Approach

1. Measure carboxyhemoglobin levels - elevated in smokers (>3-4% in light smokers, often higher in heavy smokers) 1
2. Complete blood count - to confirm elevated hematocrit/hemoglobin 1
3. Rule out other causes of secondary polycythemia:
   • Arterial blood gas to assess for hypoxemia
   • Serum erythropoietin level
   • Evaluation for underlying conditions like COPD 1

Treatment Algorithm

Step 1: Smoking Cessation

• Provide pharmacological support including nicotine replacement therapy, bupropion, and varenicline 1
• Offer behavioral interventions and counseling to support cessation 1

Step 2: Therapeutic Phlebotomy

• For patients with hematocrit >65% or symptomatic hyperviscosity 1, 3
• Remove 350-500 mL of blood per session 1
• Target hematocrit below 45% to reduce thrombotic risk 1
• Avoid aggressive phlebotomy in patients with cyanotic heart disease due to risk of stroke 3
• For COPD patients, graded phlebotomy to a hematocrit range of 55-60% may improve exercise tolerance and cardiac function 3

Step 3: Manage Underlying Conditions

• For secondary polycythemia due to chronic hypoxemia (e.g., COPD), initiate long-term oxygen therapy (LTOT) when hematocrit >55% with chronic hypoxemia 1
• Administer oxygen for at least 15 hours daily, adjusting flow to maintain SaO2 ≥90% 1

Step 4: Thrombosis Prevention

• Consider low-dose aspirin (81-100 mg daily) for patients without contraindications to reduce thrombotic risk 1, 3

Monitoring and Follow-up

• After phlebotomy, check hematocrit in 1-2 weeks 1
• Monitor iron status periodically in patients undergoing regular phlebotomy to prevent iron deficiency 1
  • Avoid inappropriate phlebotomies that can lead to iron deficiency, as microcytosis due to iron deficiency is a strong independent predictor for cerebrovascular events 3
• Complete blood count every 2-4 weeks initially, then every 3 months once stable 1
• Annual cardiovascular risk assessment 1
• Evaluate for symptoms of hyperviscosity (headache, dizziness, visual disturbances) 1

Special Considerations

Polycythemia Vera vs. Secondary Polycythemia

• If polycythemia vera is suspected (rather than smoking-induced secondary polycythemia), evaluate using WHO diagnostic criteria 1
• For confirmed polycythemia vera, consider cytoreductive therapy with hydroxyurea for high-risk patients 3

Medications for Specific Conditions

• For post-renal transplant erythrocytosis, both angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor inhibitors are effective in lowering hematocrit levels 3
• ACE inhibition has also been shown to reduce hematocrit levels in COPD-associated secondary polycythemia 3
• Theophylline has been shown to lower hematocrit levels in COPD 3

Potential Pitfalls and Caveats

1. Avoid iron deficiency - Do not perform routine phlebotomies without monitoring iron status 1, 3
2. Recognize smoking as cause of erythrocytosis - Contrary to common belief, smoking is actually associated with lower erythropoietin levels despite causing erythrocytosis 4
3. Consider thrombotic risk - Smokers have increased tissue factor expression in atherosclerotic plaques, increasing thrombogenicity 5
4. Avoid dehydration - Can worsen hyperviscosity 3
5. Recognize symptoms of hyperviscosity - Headache, visual disturbances, fatigue, and dizziness may indicate need for more aggressive management 6

By following this structured approach, the elevated hematocrit in smokers can be effectively managed to reduce morbidity and mortality associated with hyperviscosity.