white blood cell (WBC) count and differential count, a two-component blood test that first counts the total number of WBCs (leukocytes) in 1 cubic millimeter of peripheral venous blood and then measures the percentage of each type of leukocyte present in the same specimen (the differential count). The WBC and differential count are routinely measured as part of a complete blood count and, when done serially, have both diagnostic and prognostic value.
