What is the appropriate workup and management for a patient with elevated hemoglobin and hematocrit and a decreasing white blood cell count?

Workup and Management of Elevated Hemoglobin/Hematocrit with Decreasing WBC

First, exclude spurious laboratory results by repeating the complete blood count with proper technique, as overfilled collection tubes can falsely elevate hemoglobin/hematocrit and lower white blood cell counts 1.

Initial Diagnostic Workup

Once spurious results are excluded, proceed with the following systematic evaluation:

Essential Laboratory Tests

• JAK2V617F mutation testing - This is the critical first step, as JAK2 mutations are present in >95% of polycythemia vera (PV) cases and can be positive even when hemoglobin appears normal 2
• Serum erythropoietin level - Typically low or inappropriately normal in PV 3
• Iron studies (serum iron and ferritin) - Iron deficiency can mask PV by preventing full expression of erythrocytosis, creating "masked PV" with hemoglobin levels below typical diagnostic thresholds 4, 3
• Complete metabolic panel to assess renal function and exclude secondary causes 3

Additional Evaluation

• Bone marrow biopsy with morphology assessment - Required if JAK2 is positive or clinical suspicion remains high, looking for hypercellularity with trilineage growth characteristic of PV 2
• Abdominal imaging to evaluate for splenomegaly, which may indicate underlying myeloproliferative neoplasm 2
• Thrombophilia workup if there is any history of thrombosis, particularly in unusual sites like portal vein thrombosis 2

Critical Diagnostic Considerations

Masked Polycythemia Vera

Be aware that 15-35% of PV patients present with hemoglobin levels below traditional diagnostic thresholds (males <18.5 g/dL, females <16.5 g/dL) due to iron deficiency or plasma volume expansion 4. These masked PV patients:

• Are more frequently male 4
• Present with higher platelet counts 4
• Have increased bone marrow reticulin fibrosis 4
• Show worse overall survival compared to overt PV (p=0.011 by WHO criteria, p=0.0019 by BCSH criteria) 4
• Risk factors for inferior survival include age >65 years and WBC >15 × 10⁹/L 4

Unusual Presentations

PV can present with completely normal hemoglobin and hematocrit, particularly when complicated by thrombosis or blood loss 2. The decreasing WBC in your patient warrants investigation for myeloproliferative neoplasm even if other counts appear borderline or normal 2.

Management Algorithm

If Polycythemia Vera is Confirmed

Immediate Management (All Patients)

Maintain hematocrit strictly below 45% through phlebotomy - The CYTO-PV trial demonstrated that hematocrit <45% versus 45-50% reduced cardiovascular death and major thrombotic events from 9.8% to 2.7% (HR 3.91,95% CI 1.45-10.53) 5

• Induction phase: Remove 300-450 mL weekly or twice weekly until target hematocrit is reached 5
• Maintenance phase: Same volume per phlebotomy, with intervals determined by hematocrit levels 5
• Daily low-dose aspirin for all patients to reduce thrombotic risk 5

Risk Stratification for Cytoreductive Therapy

High-risk patients (age >60 years OR prior thrombotic event) require cytoreductive therapy 5:

First-line cytoreductive options 5:

• Hydroxyurea at any age, though use cautiously in young patients due to uncertain long-term leukemogenic risk 5
• Recombinant interferon-alpha (rIFNα) as alternative first-line at any age 5

Additional indications for cytoreduction 5:

• Poor tolerance to phlebotomy
• Symptomatic or progressive splenomegaly
• Severe disease-related symptoms
• Platelet count >1500 × 10⁹/L
• Leukocyte count >15 × 10⁹/L (particularly relevant given your patient's decreasing WBC - monitor trend closely)
• Iron deficiency with detrimental symptoms (pica, mouth paresthesia, esophagitis, restless legs) that worsens hematocrit when iron is supplemented 5

Second-Line Therapy

Ruxolitinib (JAK1/JAK2 inhibitor) is FDA and EMA approved for PV patients with inadequate response to or intolerance of hydroxyurea 5.

Cardiovascular Risk Management

Aggressively manage all cardiovascular risk factors including hypertension, hyperlipidemia, and smoking cessation, as thrombotic complications are the primary cause of morbidity and mortality 5.

Key Clinical Pitfalls

• Do not dismiss the diagnosis based on "normal" hemoglobin levels - masked PV exists and carries worse prognosis 4
• Do not target hematocrit of 45-50% - this range significantly increases thrombotic risk compared to <45% 5
• Do not overlook iron deficiency - it can mask the full erythrocytosis of PV and requires careful management 4, 3
• Do not ignore unusual site thrombosis - this mandates extensive workup including JAK2 analysis even with normal blood counts 2