In an asymptomatic adult with normal urea, phosphate, anion gap, calcium, and red‑cell distribution width but an elevated hemoglobin of 174 g/L, what is the most likely diagnosis and recommended management?

Elevated Hemoglobin in an Asymptomatic Adult

In an asymptomatic adult with hemoglobin 174 g/L and otherwise normal laboratory values, the most likely diagnosis is polycythemia (either primary polycythemia vera or secondary erythrocytosis), and immediate evaluation should include repeat complete blood count, peripheral blood smear, JAK2 mutation testing, and serum erythropoietin level to distinguish between these entities. 1

Interpretation of Laboratory Values

Your laboratory results show:

• Hemoglobin 174 g/L (17.4 g/dL): This exceeds the WHO threshold of 130 g/L for men and 120 g/L for women, confirming polycythemia 2
• Normal urea (7.5): Rules out significant renal dysfunction as a secondary cause
• Normal phosphate (0.79): No evidence of metabolic bone disease
• Normal anion gap (14): Within the modern reference range of 3-11 mmol/L using ion-selective electrode methods, though at the upper limit 3
• Normal RDW CV (11.4%): This is well below 12.7%, making iron deficiency highly unlikely 4
• Normal calcium (2.57): No evidence of hypercalcemia-related disorders

The combination of elevated hemoglobin with normal RDW is particularly significant, as iron deficiency typically causes RDW elevation (>13.2% in prelatent deficiency, >14.0% in latent deficiency) 4. Your normal RDW effectively excludes iron deficiency as a contributing factor 5.

Immediate Diagnostic Workup

Order the following tests immediately:

• Repeat complete blood count with red cell indices and reticulocyte count to confirm the elevation and assess bone marrow response 1
• Peripheral blood smear examination to identify morphologic abnormalities and rule out concurrent conditions 1
• JAK2 V617F mutation testing as this mutation is present in >95% of polycythemia vera cases 1
• Serum erythropoietin level to distinguish primary (low EPO) from secondary (high EPO) causes 1
• Oxygen saturation measurement to exclude hypoxia-driven erythrocytosis 1

Differential Diagnosis Priority

Primary polycythemia vera is the most concerning diagnosis requiring urgent evaluation, as untargeted hematocrit management significantly increases cardiovascular risk 1. The CYTO-PV trial demonstrated a 3.91-fold increased risk of cardiovascular events when hematocrit is maintained at 45-50% versus <45% 1.

Secondary causes to evaluate include:

• Chronic hypoxemia (sleep apnea, chronic lung disease, high altitude residence)
• Renal pathology (renal artery stenosis, polycystic kidney disease, renal tumors producing erythropoietin)
• Testosterone therapy or anabolic steroid use 1
• Smoking-related carboxyhemoglobinemia
• Dehydration or spurious polycythemia (Gaisböck syndrome)

Management Algorithm

If polycythemia vera is confirmed:

• Target hematocrit <45% in all patients through phlebotomy, as this is the single most important intervention to reduce thrombotic risk 1
• Initiate cytoreductive therapy if: age >60 years, previous thrombotic event, poor tolerance to phlebotomy, symptomatic or progressive splenomegaly, severe disease-related symptoms, or extreme thrombocytosis (>1500 × 10⁹/L) or leukocytosis (>15 × 10⁹/L) 1
• First-line cytoreductive options: hydroxyurea or recombinant interferon alpha at any age; ruxolitinib for hydroxyurea-resistant or intolerant patients 1

If secondary erythrocytosis is confirmed:

• Address the underlying cause (treat sleep apnea, optimize oxygenation, discontinue testosterone if applicable)
• Consider phlebotomy only if hematocrit remains >54% despite treating the underlying condition 1

Critical Pitfalls to Avoid

Do not dismiss elevated hemoglobin as "relative polycythemia" without proper evaluation, as this delays diagnosis of potentially serious conditions requiring specific management 1.

Do not assume the patient is asymptomatic – specifically inquire about: headaches, dizziness, visual disturbances, pruritus after bathing (aquagenic pruritus, highly specific for polycythemia vera), erythromelalgia (burning pain in extremities), early satiety or abdominal fullness (suggesting splenomegaly), and history of thrombotic events 1.

Do not wait for symptoms to develop before initiating evaluation, as the first manifestation of polycythemia vera can be a catastrophic thrombotic event 1.

Recognize that normal anion gap does not exclude early kidney disease – the traditional anion gap may not elevate until eGFR <45 ml/min per 1.73 m², though albumin-adjusted measurements show changes earlier 6. However, your normal urea makes significant renal dysfunction unlikely.