CD45 is a haematopoietic marker which is expressed on all leukocytes with variable intensity. It is absent on erythroid cells and non-haematopoietic cells. The difference in fluorescence intensity between leukocytes, in combination with different side scatter properties, can be used to distinguish various leukocyte lineages.

The analysis of SSc against CD45 expression provides a simple, reproducible method for distinguishing the major cell lines in peripheral blood and bone marrow specimens. In this example, the various lineages are labelled.