Flow cytometry is a widely used technique for quantifying cell populations in a sample, providing both absolute and relative cell counts. This analysis is essential in immunology, cancer research, hematology, and microbiology, where accurate counting of specific cell subsets is critical.
Flow cytometers measure cells based on light scattering (forward scatter [FSC] and side scatter [SSC]) and fluorescence signals from labeled markers. To determine cell counts, the following methods are commonly employed:
Relative Counting (%)
The percentage of a specific cell subset within a parent population (e.g., %CD4+ T cells among total lymphocytes) is useful for immunophenotyping but does not provide absolute numbers.
Absolute Cell Count in Microliters or Cells per Milliliter:
This method determines the exact number of cells in a given volume. It requires a reference standard, such as beads with a known count. Additionally, some cytometers perform volume-based measurements.