What clinical and laboratory findings would suggest a myeloproliferative process?

Clinical and Laboratory Indicators of Myeloproliferative Neoplasms

A myeloproliferative process is indicated by persistent unexplained cytosis (elevated blood counts), specific molecular mutations (JAK2, CALR, MPL, or BCR-ABL1), and characteristic bone marrow findings showing clonal proliferation of one or more myeloid lineages. 1

Key Diagnostic Features

Peripheral Blood Abnormalities

The hallmark presentation involves persistent elevation of one or more blood cell lines:

• Polycythemia: Hemoglobin >16.5 g/dL (men) or >16 g/dL (women) 1
• Thrombocytosis: Platelet count ≥450 × 10⁹/L 1
• Leukocytosis: Elevated white blood cell count with full spectrum of granulocytes (mature and immature) 2
• Eosinophilia: May indicate PDGFRA/PDGFRB/FGFR1-associated neoplasms 3

Critical morphologic clues on blood smear include:

• Teardrop erythrocytes (dacrocytes) suggesting myelofibrosis 4
• Leukoerythroblastosis (immature granulocytes and nucleated red cells) 2
• Left-shifted granulocytic maturation 4

Molecular Markers (Essential for Diagnosis)

The 2016 WHO criteria mandate molecular testing 1:

For Philadelphia-negative MPNs:

• JAK2 V617F mutation (most common across PV, ET, PMF) 1
• JAK2 exon 12 mutations (polycythemia vera without V617F) 3
• CALR exon 9 mutations (essential thrombocythemia and myelofibrosis) 1
• MPL mutations (thrombocythemia and myelofibrosis) 1

For Philadelphia-positive disease:

• BCR-ABL1 fusion gene confirms chronic myeloid leukemia 3

Bone Marrow Findings

Bone marrow biopsy is mandatory despite molecular findings, as no mutation is disease-defining 4:

• Hypercellularity for age with trilineage growth (panmyelosis) in polycythemia vera 3
• Megakaryocyte proliferation with large, mature, pleomorphic forms 1
• Reticulin or collagen fibrosis (grade 2-3) in overt myelofibrosis 1
• Prominent granulocytic hyperplasia in CML 2

Supporting Laboratory Features

Additional findings that strengthen the diagnosis:

• Subnormal serum erythropoietin in polycythemia vera 3
• Reduced leukocyte alkaline phosphatase (LAP) in CML 2
• Increased or normal LAP in agnogenic myeloid metaplasia 2
• Splenomegaly (palpable or imaging-confirmed) 1

Diagnostic Algorithm

1. Identify persistent cytosis on complete blood count
2. Examine peripheral blood smear for morphologic clues (teardrop cells, left shift, dysplasia)
3. Order molecular testing for JAK2 V617F, CALR, MPL, and BCR-ABL1 based on phenotype 1
4. Perform bone marrow biopsy with morphologic evaluation and cytogenetics 4
5. Measure erythropoietin level if polycythemia present 3
6. Consider Next Generation Sequencing panel for triple-negative cases or prognostic assessment (ASXL1, EZH2, TET2, IDH1/2, SRSF2) 5

Critical Pitfalls to Avoid

Do not diagnose MPN based solely on molecular findings—reactive processes can coexist with clonal markers, and bone marrow morphology remains essential for definitive classification 4. The presence of JAK2, CALR, or MPL mutations is not disease-defining; integration with histology and clinical features is mandatory 1.

Exclude reactive causes before concluding neoplastic process: infection, inflammation, iron deficiency (masked polycythemia), hypoxia, or secondary thrombocytosis must be ruled out 4.

Recognize overlap syndromes—myelodysplastic/myeloproliferative neoplasms share features of both categories and require careful morphologic assessment to distinguish from classic MPNs 3.