What are the implications of elevated red blood cell (RBC) count, hemoglobin, and hematocrit in a 50-year-old female?

Evaluation of Elevated Red Blood Cell Parameters in a 50-Year-Old Female

The elevated red blood cell count (5.55), hemoglobin (16.9), and hematocrit (50.5) in this 50-year-old female strongly suggest polycythemia vera and require prompt hematologic evaluation to rule out this myeloproliferative disorder.

Initial Assessment of Elevated Red Blood Cell Parameters

These laboratory values exceed the normal range for a female patient and warrant investigation for:

1. Polycythemia vera (PV) - a clonal myeloproliferative disorder
2. Secondary polycythemia - hypoxia-driven or hypoxia-independent
3. Relative polycythemia - due to plasma volume contraction

Laboratory Interpretation

The patient's values are significantly elevated:

• RBC count: 5.55 (elevated)
• Hemoglobin: 16.9 g/dL (elevated)
• Hematocrit: 50.5% (elevated)

These values exceed the 95th percentile for females and meet the first major criterion for polycythemia vera according to WHO diagnostic criteria 1.

Diagnostic Approach

First-Line Testing

1. Complete blood count with peripheral blood smear - already shows elevated parameters
2. JAK2 V617F mutation testing - present in approximately 95% of PV cases
3. Serum erythropoietin level - typically low in PV

Second-Line Testing

1. Bone marrow biopsy and aspiration - necessary for definitive diagnosis
2. JAK2 exon 12 mutation testing - if JAK2 V617F is negative but PV still suspected

Differential Diagnosis

1. Polycythemia Vera

• Clonal myeloproliferative disorder
• Characterized by increased red cell mass independent of erythropoietin
• Associated with JAK2 mutations in >95% of cases 1

2. Secondary Polycythemia

• Hypoxia-driven causes:
  • Chronic lung disease
  • Sleep apnea
  • High altitude
  • Smoking (carbon monoxide exposure)
• Hypoxia-independent causes:
  • Renal tumors
  • Hepatocellular carcinoma
  • Uterine leiomyoma
  • Pheochromocytoma 2

3. Relative Polycythemia

• Due to plasma volume contraction
• Causes include dehydration, diuretics, severe burns 2

Clinical Implications and Management

Immediate Concerns

• Thrombotic risk - elevated hematocrit increases blood viscosity and thrombosis risk
• Hyperviscosity symptoms - headache, dizziness, visual disturbances, fatigue

Management Approach

If polycythemia vera is confirmed:

1. Therapeutic phlebotomy - indicated when hemoglobin >20 g/dL and hematocrit >65% with symptoms of hyperviscosity 2

   • Target hematocrit <45%
   • Initial schedule: 300-500 mL every 2-3 days until target achieved

2. Low-dose aspirin (81-100 mg daily) - for all patients without contraindications to reduce thrombotic risk 1

3. Cytoreductive therapy - for high-risk patients (age >60 years and/or history of thrombosis)

   • First-line options: hydroxyurea, interferon-α
   • Second-line: ruxolitinib for those intolerant/resistant to hydroxyurea 1

Monitoring

• Regular CBC monitoring every 2-3 months initially, then every 3-6 months once stable
• Assess for disease progression, thrombotic and bleeding complications

Common Pitfalls to Avoid

1. Overlooking masked PV - where increased plasma volume conceals elevated red cell mass 1

2. Attributing findings solely to dehydration - without investigating underlying causes

3. Neglecting bone marrow examination - essential for definitive diagnosis

4. Performing unnecessary repeated phlebotomies - can lead to iron deficiency, decreased oxygen-carrying capacity, and stroke risk 2

5. Misinterpreting laboratory artifacts - certain conditions like paraproteinemias can cause falsely elevated hemoglobin readings 3

This patient requires prompt referral to a hematologist for comprehensive evaluation and management of her elevated red blood cell parameters, with particular focus on ruling out polycythemia vera.