In flow cytometry, which physical property is assessed by forward scatter?

• A. Cell size
• B. Cell granularity
• C. Fluorescence intensity
• D. Cell viability

Answer: (A)

Forward scatter reflects how big the cell is. In flow cytometry, the laser light that scatters in the forward direction increases with the cell’s size, so larger cells produce a stronger forward-scattered signal. This property is commonly used to distinguish small cells from larger ones and to gate populations by size, such as separating lymphocytes from monocytes or granulocytes. In contrast, side scatter correlates with internal complexity or granularity, fluorescence intensity comes from labeled antibodies or dyes, and viability is determined by dyes that indicate live versus dead cells. So the property assessed by forward scatter is cell size.