What do standard forward and side scatter measurements estimate?

Standard forward and side scatter measurements are critical parameters in flow cytometry that primarily provide information about cell size and granularity. Forward scatter measures the light that is scattered in the forward direction as cells pass through the laser beam, which correlates with the size of the cells. Larger cells scatter more light in this direction, leading to a higher forward scatter signal.

Meanwhile, side scatter measures the light that is scattered at a right angle to the direction of the laser beam, which provides an indication of the internal complexity or granularity of the cells. Cells with more granules or complex internal structures, such as leukocytes, will scatter more light to the sides than simpler cells.

Together, these scatter measurements offer a powerful means to differentiate between various cell types based on their physical characteristics, making them foundational for the analysis of heterogeneous cell populations. Other options, such as cell viability, DNA content, and surface marker expression, involve specific staining techniques or assays that go beyond standard scatter analysis.