What are the key lab findings in diagnosing and managing myelofibrosis?

Key Laboratory Findings in Myelofibrosis

The diagnosis of myelofibrosis requires a comprehensive panel of laboratory tests including complete blood count with differential, bone marrow examination, molecular testing for JAK2, CALR, and MPL mutations, and cytogenetic studies to accurately identify the disease and stratify risk. 1

Essential Diagnostic Laboratory Tests

Blood Tests

• Complete blood count (CBC) with differential

  • Anemia (common finding in overtly fibrotic MF) 1
  • Leukoerythroblastosis (immature WBCs and nucleated RBCs in peripheral blood) 1
  • Variable leukocyte count (can be increased, normal, or decreased)
  • Variable platelet count (can be increased, normal, or decreased)
  • Peripheral blood smear showing teardrop-shaped red cells (dacryocytes) 1
  • Anisopoikilocytosis (abnormal RBC size and shape) 2

• Chemistry Panel

  • Elevated serum lactate dehydrogenase (LDH) - key minor criterion 1
  • Comprehensive metabolic panel with uric acid 1
  • Liver function tests 1

Bone Marrow Studies

• Bone marrow aspirate and biopsy with trichrome and reticulin stain (essential) 1

  • Megakaryocyte proliferation and atypia (major criterion) 1
  • Reticulin and/or collagen fibrosis (in overtly fibrotic MF) 1
  • Hypercellularity with granulocytic proliferation (in prefibrotic MF) 1
  • Decreased erythropoiesis 1

• Bone marrow cytogenetics (karyotype ± FISH) 1

  • Prognostically important abnormalities:
    • Very high-risk: -7, inv(3), i(17q), +21, +19, 12p- and 11q- 3
    • Favorable: normal karyotype or isolated +9, 13q-, 20q-, 1q abnormalities, loss of Y 3

Molecular Testing

• JAK2 V617F mutation (found in ~60% of MF cases) 1, 4
• CALR mutation testing (if JAK2 negative) 1, 4
• MPL mutation testing (if JAK2 and CALR negative) 1, 4
• Additional molecular testing for high-risk mutations:
  • ASXL1, SRSF2, and U2AF1-Q157 (predict inferior survival) 3
  • RAS/CBL mutations (predict resistance to ruxolitinib therapy) 3

Additional Supportive Tests

• Serum erythropoietin (EPO) level 1
• Serum iron studies 1
• Coagulation tests to evaluate for acquired von Willebrand disease 1
• CD34 assessment by immunohistochemistry (helpful for blast quantification) 1

Risk Stratification Laboratory Parameters

• Hemoglobin <10 g/dL
• Leukocytes >25 × 10^9/L
• Circulating blasts ≥1%
• Platelet count <100 × 10^9/L

Diagnostic Pitfalls and Considerations

1. Distinguishing prefibrotic from overtly fibrotic MF:

   • Prefibrotic MF may present with thrombocytosis and minimal fibrosis, resembling essential thrombocythemia 1
   • Careful assessment of megakaryocyte morphology is crucial 1

2. Excluding other conditions:

   • BCR-ABL1 testing to rule out chronic myeloid leukemia 1
   • Excluding myelodysplastic syndromes with fibrosis 1
   • Ruling out reactive causes of bone marrow fibrosis 1

3. Triple-negative cases:

   • About 8-10% of MF cases lack JAK2, CALR, and MPL mutations 4, 3
   • Diagnosis relies more heavily on morphologic criteria in these cases

4. Monitoring disease progression:

   • Regular monitoring of blood counts every 3-6 months 1
   • Repeat bone marrow examination when clinically indicated 1

Management-Related Laboratory Monitoring

• Assessment of symptom burden using MPN Symptom Assessment Form (MPN-SAF) 1
• Human leukocyte antigen (HLA) testing if considering allogeneic hematopoietic cell transplant 1
• Regular monitoring of blood counts during treatment 1
• Monitoring response to therapy using the 2013 IWG-MRT and ELN Response Criteria 1

The laboratory evaluation of myelofibrosis is complex and requires integration of multiple parameters. The diagnosis cannot be made on any single test but requires a constellation of findings, with bone marrow morphology and molecular testing being particularly important.