Pathology

Pathology/C/1

Diagnostic methods of hematology (biopsy, flow cytometry, histochemical, cytogenetic, molecular diagnosis)

血液学の診断法（生検・フローサイトメトリー等）

タグ
Score / スコアHigh-yield / ポイント

1. Big picture (what you actually do in hematopathology)

In hematologic/lymphoid disorders, diagnosis is integrative:

Clinical picture + morphology + phenotype + genotype → a defined ENTITY.

So the “tests” are chosen to answer four questions:

  1. What cells are abnormal and how do they look?

  2. Which lineage / stage are they?

  3. Is there clonality / a defining genetic lesion?

  4. What is the extent (blood vs marrow vs node)?

2. Sampling sites (where the information comes from)

1) Peripheral blood

  • Quantitative: CBC (Hb, Hct, WBC, platelets), differential count
  • Qualitative: peripheral smear morphology (blasts? left shift? dysplasia? hemolysis features?)

2) Bone marrow

Two complementary specimens:

  • Bone marrow aspirate (cytology)
    • Fluid sample; best for cell details, differential counts, iron stain, cytochemistry, flow
  • Core / trephine biopsy (histology)
    • Solid sample; best for overall architecture
    • Cellularity, fibrosis, focal infiltrates, granulomas, metastatic deposits, pattern of involvement

3) Lymph node

  • Aspirate (cytology): quick look, sometimes limited
  • Excisional biopsy (histology): best for architectural patterns (follicular vs diffuse, sinus involvement, etc.)

3. Cytochemistry (enzyme stains) — “what do these blasts do?”

  • Enzymatic reactions used mainly in acute leukemias:
    • MPO (myeloperoxidase)
    • SBB (Sudan Black B)
    • NaAc (naphthol AS-D chloroacetate esterase)
  • Helps separate myeloid vs lymphoid differentiation when morphology is unclear.

4. Flow cytometry — immunophenotype on cell suspension

Definition: technique that detects/measures physical and chemical characteristics of a population of cells/particles.

  • Uses antibodies to define lineage and maturation stage.
  • Typical use: leukemias/lymphomas in blood/marrow/aspirates.

5. Immunohistochemistry (IHC) — immunophenotype in tissue sections

  • Antibodies applied on histologic samples (biopsy).
  • Helps classify lymphomas and identify cell lineage in tissue.

Lineage-specific markers (examples)

  • Granulocytes: CD33, CD13, CD15
  • Erythroid: Glycophorin A
  • Megakaryocytes: CD64 (as listed in the notes)
  • Monocytes: CD14
  • B-cells: CD19, CD20, CD49a
  • T-cells: CD3, CD2, CD5, CD4/CD8
  • NK cells: CD56, granzyme B, TIA-1

Markers suggesting acute leukemia / immaturity

  • CD34, TdT

6. Cytogenetics

Two main “levels”:

  • Metaphase cytogenetics (karyotype): large chromosomal abnormalities
  • Interphase FISH: targeted detection of
    • numeric changes (e.g., trisomy)
    • deletions (e.g., del(5q))
    • translocations (e.g., t(14;18))
    • amplifications (e.g., c-MYC)

7. Molecular diagnostics

  • Detects lesions at DNA/RNA level:
    • translocations / fusion genes
    • point mutations (e.g., JAK2 V617F)
    • expression profiling
    • gene sequencing

💡 High-yield: Hematopathology diagnosis is integrated: morphology (blood/marrow/node) + immunophenotype (flow/IHC) + genetics (karyotype/FISH/molecular) → final ENTITY.