A blood cell is a cellular component of blood, including red blood cells and white blood cells. Red blood cells transport oxygen using hemoglobin; white blood cells participate in the immune system. The usual blood-count categories also include platelets, which in humans are cell fragments rather than complete nucleated biological cells.[ref]
Blood Tests by the National Heart Lung and Blood Institute. Complete blood count, red cells, white cells, platelets and haemoglobin
Conversely, a mature human red blood cell is a whole specialized biological cell without a cell nucleus; possessing a cell nucleus is not a universal test for membership.The Coulter counter connects cell counting to electric current. Wallace H. Coulter's patent passes a diluted suspension through a narrow conducting path between electrodes. A particle changes the electric current as it passes, yielding a countable pulse. The known sampled volume and dilution convert counts to an estimate for the original sample; simultaneous passage of particles can mask events.[ref]
Means for counting particles suspended in a fluid by Wallace H. Coulter. US2656508A, description of Figs.1–4 and 6–7; dilution and masking
For a synthetic arithmetic example, count 5,000 cells in of a sample diluted by a factor of 1,000. The original sample then contains an estimated cells per microlitre. This illustrates counting and dilution, not a clinical reference range. A pulse alone does not establish which cell type produced it; the preparation and classification method must specify that.
