Immunohaematology studies the reactions that take place between antigens present on blood cells and antibodies present in plasma. Patients undergoing transfusion therapy are tested for their ABO and RhD blood groups and the presence of any antibodies that may cause a reaction between their plasma and donor red cells. A range of tests are available to use to detect and identify antibodies in the patient's plasma from simple tube and gel tests to more complex absorption and elution techniques as well as advanced molecular techniques. These same tests will also identify if the antigen is present on the patient's red cells. For patients with haematological conditions such as auto immune haemolytic anaemia, a wide range of immune-haematological techniques are used to identify and resolve the diagnostic problems in these patients. Molecular techniques are increasingly used in immunohaematology to determine the antigen profile of patients, resolve complex problems and large scale red cell typing.