D antigen is a protein found on the surface of red blood cells. It is often known as the Rh factor and indicates your blood type. People are either D (Rh) negative or D (Rh) positive. Absence of the D antigen is identified as D or Rh negative. D positive is easily identified whereas it is difficult to check and confirm the presence of the D negative. Rh negativity becomes an issue during pregnancy when you have Rh negative while your baby has Rh positive. It can cause haemolytic disease to the baby which consequently leads to anemia and sometimes even death. Du Test test is performed on the blood sample to measure the level of Weak D Antigen in the blood. It confirms Rh Negativity and is also administered during and after Rh negativity treatment.