The CD34 Flow Cytometry test is used to detect and quantify hematopoietic stem and progenitor cells in blood, bone marrow, or mobilized peripheral blood. CD34 is a transmembrane glycoprotein expressed on early hematopoietic and progenitor cells, as well as endothelial progenitor cells. This marker is critical for evaluating stem cell populations for transplantation, monitoring bone marrow recovery, and assessing certain hematologic disorders.