In a 54-year-old male smoker (≈20 cigarettes/day) with markedly elevated hemoglobin (182 g/L) and hematocrit (0.565) and otherwise normal full blood count, what is the most likely diagnosis and recommended management?

Smoking-Related Secondary Polycythemia

This is smoking-related secondary polycythemia (smoker's polycythemia), and the primary management is immediate smoking cessation with close monitoring of blood counts.

Diagnosis

The presentation is classic for smoker's polycythemia in a heavy smoker (20 cigarettes/day):

• Elevated hemoglobin (182 g/L) and hematocrit (0.565) with otherwise normal CBC parameters
• Normal MCV (96 fL) rules out macrocytosis as a contributing factor 1
• Normal white cell and platelet counts argue against primary myeloproliferative neoplasm

Key Pathophysiology

Chronic cigarette smoking causes polycythemia through two mechanisms 2:

1. Carbon monoxide exposure elevates carboxyhemoglobin (COHb) levels, typically 3-5% in smokers but can reach 5.6% with one pack/day 3. As a general rule, COHb rises approximately 2.5% per pack smoked daily 3
2. Left-shifted oxygen-hemoglobin dissociation curve from elevated COHb reduces tissue oxygen delivery, stimulating compensatory erythrocytosis 2
3. Contrary to traditional belief, EPO levels are actually lower in smokers despite elevated hematocrit 4

Diagnostic Workup Required

Measure carboxyhemoglobin level using laboratory CO-oximetry (not pulse oximetry, which cannot differentiate COHb) 3. COHb levels ≥10% in smokers are considered outside expected physiological range 3.

Rule out primary polycythemia vera by checking:

• JAK2 V617F mutation (should be negative in smoking-related polycythemia) 5, 6
• Serum erythropoietin level (typically subnormal in PV, but paradoxically lower in smokers) 5, 4

Management Algorithm

Immediate Action

1. Counsel on smoking cessation - this is the definitive treatment 2
2. Offer pharmacotherapy: varenicline (first-line), bupropion, or nicotine replacement therapy 7, 8
3. Assess for symptoms of hyperviscosity: headache, fatigue, syncope (reported in smoker's polycythemia) 2

Monitoring Strategy

• Recheck CBC in 4-6 weeks after smoking reduction/cessation
• In documented cases, hemoglobin and hematocrit normalize with smoking cessation 2
• Red cell volume decreases markedly in patients who successfully quit 2

Phlebotomy Considerations

Phlebotomy is NOT routinely indicated unless:

• Hemoglobin >20 g/dL AND hematocrit >65% with symptomatic hyperviscosity 9
• Evidence of dehydration must be excluded first 9
• If performed, always replace with equal volume of saline/dextrose 9

Avoid repeated routine phlebotomies - these deplete iron stores, create microcytic red cells with reduced oxygen-carrying capacity, and paradoxically increase stroke risk 9.

Critical Pitfalls to Avoid

1. Do not assume this is polycythemia vera without checking JAK2 mutation - smoking is a common and reversible cause 2, 6
2. Do not rely on pulse oximetry - standard devices cannot detect carboxyhemoglobin and will show falsely normal SpO2 even with COHb levels of 25% 3
3. Do not perform aggressive phlebotomy - this causes more harm than benefit in secondary polycythemia 9
4. Do not ignore cardiovascular risk factors - manage hypertension, lipids, and consider antiplatelet therapy if indicated for cardiovascular disease 10, 11

Expected Outcomes

With successful smoking cessation 2:

• Symptoms (fatigue, headache) resolve completely
• Elevated red cell volume decreases markedly
• Low plasma volume increases (if present)
• Normalization typically occurs within weeks to months

The prognosis is excellent with smoking cessation, making this a highly treatable condition that directly impacts both morbidity and quality of life.