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Cytogenetics

Prepare Accurate Karyograms

The karyogram is the formalized visual output of the cytogenetic analysis. It is constructed by capturing digital images of metaphase spreads and arranging the chromosomes according to international standards

Select Representative Images

  • Technical Quality
    • Resolution: Select the cell with the best banding (longest chromosomes). High resolution proves the ability to detect subtle defects
    • Spreading: Select cells with minimal overlaps (avoids digital artifacts) and intact metaphase plates
    • Contrast: Avoid “puffy” or “black” chromosomes
  • Diagnostic Relevance
    • Representative: The image must match the diagnosis. If the patient is reported as Normal (46,XY), do not karyotype a random broken cell (45,X)
    • Abnormal: Select cells that clearly display the specific abnormality (e.g., breakpoints of a translocation)
    • Mosaicism: Select representative cells from both the normal and abnormal populations

Arrange Chromosomes Using an Approved Format

  • ISCN Layout
    • Grouping: Chromosomes are arranged in Groups A through G based on size and centromere position
    • Orientation: p-arm (short) at the top; q-arm (long) at the bottom. Centromeres aligned horizontally
    • Homologs: Normal pairs are placed side-by-side
  • Abnormalities
    • Derivative Chromosomes: Placed to the right of their normal homolog (e.g., Normal 9, then Derivative 9). This allows direct comparison
    • Markers: Unidentified chromosomes are placed at the end, after Sex Chromosomes
  • Verification: Automated software classifiers often misidentify chromosomes (especially C-group). The laboratory scientist must manually verify every assignment

Prepare Appropriate Number of Karyograms

  • Standard Rule: A minimum of 2 Karyograms is standard for almost all cases
  • Scenario Specifics
    • Normal: 2 Normal Karyograms
    • Clonal Abnormal: 2 Abnormal Karyograms (visually proving clonality)
    • Mosaic/Evolution: 1 Karyogram of Clone A + 1 Karyogram of Clone B (visually proving the existence of multiple lines)
  • Goal: The set of images must serve as definitive visual proof of the reported ISCN string