MODEL RELEASED. Counting blood cells. Male technician analysing blood using a Coulter counter. Blood samples are seen in purple-topped tubes along the front of the machine. The Coulter counter counts and measures the sizes of red, white and platelet blood cells in any given sample and displays the results on computer monitors (upper left & right). A low count of red blood cells is a sign of anaemia. Similarly high numbers of immature, small white blood cells indicate leukaemia. The Coulter counter can also estimate the haemoglobin content of red blood cells.