In a 75-year-old woman with elevated red blood cell count, hemoglobin, hematocrit, high mean platelet volume (13.2 fL), and absolute monocyte count of 1,134/µL, what diagnostic workup and initial management are recommended?

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Workup for Suspected Myeloproliferative Neoplasm

This presentation of erythrocytosis (elevated RBC, hemoglobin, hematocrit), elevated mean platelet volume (13.2 fL), and absolute monocytosis (1,134/µL) in a 75-year-old woman requires immediate JAK2 mutation testing to evaluate for polycythemia vera (PV), followed by bone marrow biopsy if mutation-positive, as this constellation strongly suggests a Philadelphia chromosome-negative myeloproliferative neoplasm.

Diagnostic Algorithm

First-Line Testing (Immediate)

JAK2 mutation screening is the critical first step 1, 2:

  • Test for JAK2V617F mutation (found in ≥95% of PV cases)
  • If negative, test for JAK2 exon 12 mutations (found in 2-4% of PV patients)
  • Use whole blood or purified granulocytes with detection sensitivity of ≥1%

Serum erythropoietin (EPO) level 3:

  • Subnormal EPO strongly supports PV diagnosis (minor criterion per WHO)
  • Helps distinguish clonal from secondary erythrocytosis
  • Essential for differentiating PV from other causes of erythrocytosis

Interpretation Based on JAK2 Results

If JAK2-positive:

  • Proceed to bone marrow biopsy with reticulin staining 1, 2
  • Look for trilineage myeloproliferation with pleomorphic, mature megakaryocytes
  • Assess for reticulin fibrosis (grade on 0-3 scale)
  • The elevated MPV (13.2 fL, above typical normal of ~11 fL) and monocytosis suggest active myeloproliferation

PV diagnosis requires 1, 2:

  • Both major criteria: (1) Hemoglobin >16.5 g/dL in women or >18.5 g/dL in men, AND (2) JAK2 mutation
  • Plus one minor criterion: bone marrow trilineage myeloproliferation OR subnormal serum EPO

If JAK2-negative:

  • Consider CALR and MPL mutations (found in ~60-80% of JAK2-negative ET/PMF cases) 2
  • Evaluate for secondary causes of erythrocytosis 3:
    • Cardiopulmonary disease (central hypoxia)
    • Renal artery stenosis (peripheral hypoxia)
    • EPO-producing tumors (renal cell carcinoma, hemangioblastoma)
    • Medication review: testosterone, erythropoiesis-stimulating agents, SGLT2 inhibitors
  • Consider hereditary erythrocytosis if longstanding history or family history present

Additional Baseline Studies

  • Complete metabolic panel with lactate dehydrogenase (LDH)
  • Ferritin level (iron deficiency common in PV; affects hematocrit-to-hemoglobin ratio) 4
  • Peripheral blood smear review for leukoerythroblastosis, blast cells
  • Abdominal imaging (ultrasound or CT) to assess spleen size

Risk Stratification if PV Confirmed

Age >60 years alone places this patient in high-risk category 2:

  • High risk = age >60 years OR previous thrombosis
  • This patient's age (75 years) mandates cytoreductive therapy consideration

Additional thrombotic risk factors to assess 2:

  • Cardiovascular risk factors (hypertension, diabetes, hyperlipidemia, smoking)
  • Previous thrombotic events
  • Leukocytosis (WBC >15 × 10⁹/L associated with worse outcomes)

Initial Management Considerations

If PV is confirmed:

Cytoreductive therapy is indicated given high-risk status (age >60):

  • Hydroxyurea is first-line cytoreductive agent
  • Target hematocrit <45% in all patients (associated with reduced thrombotic risk)

Aspirin 81-100 mg daily unless contraindicated 2:

  • Reduces thrombotic risk
  • Contraindications: active bleeding, severe thrombocytopenia, acquired von Willebrand syndrome

Phlebotomy to achieve hematocrit target:

  • However, note that phlebotomy alone (without cytoreduction) may paradoxically increase thrombotic risk in PV compared to chemotherapy 5
  • Iron deficiency from phlebotomy can worsen symptoms and increase thrombosis risk 4

Cardiovascular risk optimization:

  • Control hypertension, diabetes, hyperlipidemia
  • Smoking cessation

Critical Pitfalls to Avoid

  1. Do not assume elevated hematocrit alone determines thrombotic risk 5: Thrombosis in erythrocytosis involves multiple factors beyond viscosity, including clonal myeloproliferation effects on platelets and leukocytes

  2. Do not diagnose "idiopathic erythrocytosis" prematurely 3: This diagnosis requires exhaustive evaluation including complete mutation screening and exclusion of all secondary causes

  3. Do not use indiscriminate phlebotomy in non-clonal erythrocytosis 3: Evidence for benefit is lacking and may cause harm through iron deficiency

  4. Do not overlook the monocytosis (1,134/µL): While reference ranges vary, this is at the upper limit and supports active myeloproliferation; monitor for progression to myelofibrosis

  5. The elevated MPV (13.2 fL) is significant: This suggests qualitative platelet abnormalities typical of MPNs and may contribute to thrombotic risk independent of platelet count 6

Monitoring for Disease Progression

If PV confirmed, assess for progression to post-PV myelofibrosis by monitoring for 2:

  • Development of anemia or loss of phlebotomy requirement
  • Leukoerythroblastic blood picture
  • Progressive splenomegaly (≥5 cm increase)
  • Constitutional symptoms (>10% weight loss, night sweats, fever >37.5°C)
  • Bone marrow fibrosis grade ≥2 on repeat biopsy if clinically indicated

References

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