What are the recommended initial diagnostic steps and first‑line management for a patient with suspected myeloproliferative disease (e.g., polycythemia vera, essential thrombocythemia, primary myelofibrosis)?

Myeloproliferative Disease: Initial Diagnostic Steps and First-Line Management

Begin with complete blood count, peripheral blood smear, JAK2 V617F mutation testing, and bone marrow biopsy with aspirate to establish the specific diagnosis among polycythemia vera, essential thrombocythemia, or primary myelofibrosis, then initiate risk-stratified therapy focused on preventing thrombohemorrhagic complications. 1

Initial Diagnostic Algorithm

Step 1: Laboratory Evaluation

Complete blood count with differential is mandatory to identify the predominant cell line elevation:

• Polycythemia vera: Hemoglobin ≥18.5 g/dL (men) or ≥16.5 g/dL (women), or sustained increase of ≥2 g/dL from baseline even within normal ranges 1, 2
• Essential thrombocythemia: Sustained platelet count ≥450 × 10⁹/L on repeat testing 1, 3
• Primary myelofibrosis: Leukoerythroblastosis, anemia, elevated lactate dehydrogenase, and splenomegaly 1

Peripheral blood smear examination must assess:

• Leukocytosis (present in ~49% of PV cases, often >10 × 10⁹/L) 2
• Platelet morphology and count (frequently >400 × 10⁹/L in PV; ≥450 × 10⁹/L in ET) 1, 2
• Presence of nucleated red blood cells and immature granulocytes suggesting myelofibrosis 2

Step 2: Molecular Testing

JAK2 V617F mutation testing is first-line and diagnostic:

• Present in >95% of polycythemia vera cases 2, 4, 5
• Present in ~50-60% of essential thrombocythemia cases 3, 4, 5
• Present in ~50% of primary myelofibrosis cases 3, 6

If JAK2 V617F is negative, proceed sequentially:

• JAK2 exon 12 mutation testing (for suspected PV) 2
• CALR and MPL mutation analysis (for suspected ET or PMF) 3, 4, 5

Step 3: Exclude Secondary Causes

Before confirming primary myeloproliferative disease, rule out reactive conditions:

• Iron studies (ferritin, serum iron, TIBC) to exclude iron deficiency causing secondary thrombocytosis or masking PV 2, 3
• Serum erythropoietin level: Low or inappropriately normal supports PV diagnosis (>90% specificity); high suggests secondary polycythemia 2, 3
• BCR-ABL1 testing to exclude chronic myeloid leukemia 1, 3
• Infection screening (HIV, hepatitis C, Helicobacter pylori, parvovirus, cytomegalovirus) as these can cause reactive thrombocytosis 7, 3

Step 4: Bone Marrow Examination

Bone marrow biopsy with aspirate is mandatory before initiating cytoreductive therapy and essential for distinguishing between entities: 1

Polycythemia vera findings:

• Hypercellularity for age with trilineage growth (panmyelosis) 1, 2
• Prominent erythroid, granulocytic, and megakaryocytic proliferation 1

Essential thrombocythemia findings:

• Proliferation mainly of megakaryocytic lineage with increased numbers of enlarged, mature megakaryocytes with deeply lobulated and hyperlobulated nuclei 1
• No significant increase or left shift of neutrophil granulopoiesis or erythropoiesis 1
• Absent or minimal reticulin fibrosis 1, 7

Primary myelofibrosis findings:

• Megakaryocyte proliferation and atypia with aberrant nuclear/cytoplasmic ratio, hyperchromatic, bulbous or irregularly folded nuclei, and dense clustering 1, 3
• Reticulin and/or collagen fibrosis (or prefibrotic cellular-phase disease) 1, 3
• Marked hypercellularity with prominent granulocyte proliferation and left-shifted forms 1

Critical pitfall: Distinguishing essential thrombocythemia from prefibrotic primary myelofibrosis is essential, as the latter has worse prognosis with higher rates of myelofibrotic transformation and inferior survival 1, 4, 5

Formal Diagnostic Criteria Application

Polycythemia Vera (WHO 2008 Criteria)

Diagnosis requires both major criteria plus one minor criterion, OR the first major criterion plus two minor criteria: 1

Major criteria:

• Hemoglobin ≥18.5 g/dL (men) or ≥16.5 g/dL (women), or other evidence of increased RBC volume 1
• Presence of JAK2 V617F or JAK2 exon 12 mutation 1

Minor criteria:

• Bone marrow biopsy showing hypercellularity with trilineage growth 1
• Serum erythropoietin below normal reference range 1
• Endogenous erythroid colony formation in vitro 1

Essential Thrombocythemia (WHO 2008 Criteria)

All four criteria must be met: 1

1. Sustained platelet count ≥450 × 10⁹/L 1
2. Bone marrow biopsy showing proliferation mainly of megakaryocytic lineage with increased numbers of enlarged, mature megakaryocytes; no significant increase or left shift of neutrophil granulopoiesis or erythropoiesis 1
3. Not meeting WHO criteria for PV, PMF, CML, MDS, or other myeloid neoplasm 1
4. Demonstration of JAK2 V617F or other clonal marker (CALR, MPL), or in absence of clonal marker, no evidence for reactive thrombocytosis 1

Primary Myelofibrosis (WHO 2008 Criteria)

All three major criteria and two minor criteria required: 1

Major criteria:

• Presence of megakaryocyte proliferation and atypia, usually accompanied by reticulin and/or collagen fibrosis 1
• Not meeting WHO criteria for PV, CML, MDS, or other myeloid neoplasm 1
• Demonstration of JAK2 V617F or other clonal marker (MPL W515K/L), or in absence of clonal marker, no evidence of secondary bone marrow fibrosis 1

Minor criteria:

• Leukoerythroblastosis 1
• Increased serum lactate dehydrogenase 1
• Anemia 1
• Splenomegaly 1

First-Line Management by Disease and Risk Category

Polycythemia Vera

Risk stratification divides patients into two categories: 1, 4, 5

• High risk: Age >60 years OR prior thrombosis history 1, 4, 5
• Low risk: Age ≤60 years AND no prior thrombosis history 1, 4, 5

Low-risk polycythemia vera management:

• Phlebotomy to maintain hematocrit <45% (based on CYTO-PV study showing reduced cardiovascular death and major thrombosis) 1, 4, 5
• Aspirin 81-100 mg once daily for vascular symptoms, unless contraindications exist 1, 4, 5
• Manage cardiovascular risk factors aggressively 1
• Monitor every 3-6 months for indications of cytoreductive therapy or disease progression 1

High-risk polycythemia vera management:

• Phlebotomy to maintain hematocrit <45% 1, 4, 5
• Aspirin 81-100 mg once or twice daily 1, 4, 5
• Cytoreductive therapy with hydroxyurea as first-line agent 4, 5
• Second-line options: Interferon-α or busulfan if hydroxyurea fails or is not tolerated 4, 5

Indications for cytoreductive therapy in initially low-risk patients:

• New thrombosis or disease-related major bleeding 1
• Frequent/persistent need for phlebotomy with poor tolerance 1
• Symptomatic or progressive splenomegaly 1
• Symptomatic thrombocytosis 1
• Progressive leukocytosis 1
• Progressive disease-related symptoms (pruritus, night sweats, fatigue) 1

Essential Thrombocythemia

Risk stratification uses four categories: 4, 5

• Very low risk: Age ≤60 years, no thrombosis history, JAK2 wild-type 4, 5
• Low risk: Age ≤60 years, no thrombosis history, JAK2 mutation present 4, 5
• Intermediate risk: Age >60 years, no thrombosis history, JAK2 wild-type 4, 5
• High risk: Thrombosis history present OR age >60 years with JAK2 mutation 4, 5

Very low-risk essential thrombocythemia:

• Observation without therapy may be appropriate 4, 5

Low-risk essential thrombocythemia:

• Aspirin 81 mg once or twice daily 4, 5

Intermediate-risk essential thrombocythemia:

• Cytoreductive therapy is not mandatory but consider based on individual factors 4, 5
• Aspirin therapy recommended 4, 5

High-risk essential thrombocythemia:

• Cytoreductive therapy with hydroxyurea as first-line agent 4, 5
• Aspirin 81 mg once or twice daily 4, 5
• Second-line options: Interferon-α or busulfan 4, 5

Primary Myelofibrosis

Management is more complex and depends on prognostic scoring systems incorporating age, anemia, leukocytosis, blast cells, and constitutional symptoms. 8 Specific first-line therapy recommendations require risk stratification beyond the scope of initial diagnostic management, but JAK2 inhibitors (ruxolitinib) have transformed treatment for symptomatic disease. 1

Critical Pitfalls to Avoid

Verify adequate hydration before diagnosing polycythemia vera, as dehydration is the most common cause of falsely elevated hematocrit. 2

Check MCHC and iron studies if <32%, as iron deficiency can mask true erythrocytosis in PV by normalizing hemoglobin levels. 2, 3

Do not diagnose essential thrombocythemia without bone marrow examination to exclude prefibrotic primary myelofibrosis, which has significantly worse prognosis. 1, 4, 5

Perform bone marrow biopsy before initiating cytoreductive therapy to rule out disease progression to myelofibrosis. 1

Extreme thrombocytosis (≥1,000 × 10⁹/L) paradoxically increases bleeding risk due to acquired von Willebrand disease; platelet counts >1,500 × 10⁹/L mandate cytoreductive therapy. 2

Leukocytosis >15 × 10⁹/L is a risk factor for inferior survival and increased thrombotic risk in PV. 2

Secondary thrombocytosis rarely causes thrombosis even at very high platelet counts and does not require antiplatelet therapy; treat the underlying condition instead. 3