Skip to main content

Cytogenetics

Selection, Analysis, & Documentation

The cytogenetic workflow transforms raw biological material into a precise clinical diagnosis through a series of rigorous selection, analysis, and documentation steps

Select & Analyze Suitable Metaphases

  • Select, Count, and Analyze
    • Scan slides for metaphases with optimal Spreading: (no overlaps) and Resolution (400–550 bands)
    • Count: 20 cells to detect numerical aneuploidy
    • Analyze: (Karyotype) 5–20 cells band-for-band to detect structural defects
  • Review Previous Results
    • Compare with prior karyotypes to detect Disease Progression: (Clonal Evolution) or Remission
    • Check parental studies in prenatal cases to distinguish de novo vs. familial defects
  • Sample Size
    • Constitutional: 20 Count / 5 Analyze
    • Oncology: 20 Count / 20 Analyze
    • Mosaicism: Extend count to 30–50 cells if a single abnormal cell is found
  • Culture Rule: Analyze cells from at least 2 independent cultures to rule out in vitro artifacts (Pseudomosaicism)
  • Troubleshooting
    • Poor Banding: Report “Limited Resolution.”
    • Random Loss: Ignore inconsistent losses (broken cells)

Prepare Accurate Karyograms

  • Image Selection
    • Select representative images that match the diagnosis (e.g., if reported as Mosaic, show both cell lines)
    • Choose the highest resolution, non-overlapping cell available
  • Format (ISCN Layout)
    • Arrange chromosomes in Groups A–G based on size/centromere
    • Orientation: p-arm Up, q-arm Down
    • Abnormalities: Place derivative/deleted chromosomes to the right of their normal homolog
  • Number of Images
    • Standard: 2 Karyograms
    • Mosaic/Evolution: 1 of each clone

Evaluate Abnormalities & Clinical Implications

  • Constitutional (Germline)
    • Numerical: Trisomy 21 (Down), 13, 18, 45,X (Turner), 47,XXY (Klinefelter)
    • Structural: Microdeletions (DiGeorge), Balanced Translocations (Infertility risk)
  • Acquired (Somatic/Cancer)
    • Diagnosis: t(9;22) (CML), t(15;17) (APL)
    • Prognosis: del(5q) (Good), Monosomy 7 (Poor), Complex (Poor)
  • Artifacts & Variants
    • Culture Artifact: Single cell abnormality (pseudomosaicism)
    • Normal Variants: inv(9), 1qh+, prominent satellites. Benign; do not report as pathologic

Use an Established Format (ISCN)

  • Structure: <Total>,<Sex>,<Abnormality>[<Cells>]
  • Examples
    • Normal: 46,XY[20]
    • Abnormal: 46,XY,t(9;22)(q34;q11.2)[20]
    • Mosaic: 45,X[15]/46,XX[5]
  • Key Symbols: + (Gain), - (Loss), t (Translocation), del (Deletion), inv (Inversion), der (Derivative)
  • Preliminary Results: Interim reports (usually FISH) for urgent cases (APL). Must be labeled “Preliminary.”