Blood testing. Sample of blood from a potential blood donor being tested for anaemia. The blood is dropped into the blue copper sulphate solution. If the drop floats, it indicates low levels of haemoglobin, meaning that the person may be anaemic and that a blood donation could be potentially harmful to them. Haemoglobin is the red-coloured pigment in red blood cells that is involved in oxygen transport. If blood is removed from a person with anaemia, the remaining blood may not be sufficient to deliver oxygen to the body's cells. Donated blood is given to patients in transfusions to replace lost blood, for example during surgical procedures or after accidents.