Flow cytometry offers a powerful platform for detecting and characterizing CTCs among millions of leukocytes. With proper panel design and rare-event analysis principles, reliable CTC data can be produced.
Standard CTC Panel
- CD45 (FITC): leukocyte negative selection — CD45-negative cells are CTC candidates
- CK (PE): cytokeratin — epithelial cell marker
- EpCAM (APC): epithelial cell adhesion molecule
- DAPI: nuclear staining — confirms intact cells
- Viability dye: excludes dead cells
Rules of Rare-Event Analysis
- Sufficient total events: 500,000–1,000,000 leukocytes must be collected
- Confusion matrix: the specificity of the CD45−/CK+ definition must be verified with spike-in controls
- LOD determination: the background level must be established with healthy-donor negative controls
- Dual-positive controls: EpCAM+/CK+ and CD45−/DAPI+ cells must be interpreted together
Gating Strategy
Typical CTC gating: FSC/SSC cell selection → singlet discrimination → viability → CD45 negative selection → CK and EpCAM positive detection. Every step is verified with controls.
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Rx-only — prescription screening test. Galleri® is not a diagnostic test. A positive result does not mean a cancer diagnosis; a negative result does not rule out cancer. The test does not replace the routine cancer screenings recommended by your physician. Galleri® does not detect all cancers.