MODEL RELEASED. Counting blood cells. Female technician analysing blood using a Coulter counter (at right). Blood samples stand in tubes in a rack in front of her. The Coulter counter counts and measures the sizes of red, white and platelet blood cells in any given sample and displays the results on a computer screen (at centre). 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.