For effective treatment of a disease, early diagnosis and understanding its pathophysiology is very important. Using conventional method of diagnosis (serum and urine analysis), early detection is not possible. Recombinant DNA technology, polymerase chain reaction (PCR) and Enzyme linked Immuno sorbent Assay (ELISA) are some of the techniques that serves the purpose of early diagnosis. Very low concentratin of pathogen (bacteria, viruses) can be defectd in early stage by amplication of their nucleic acid by PCR. PCR is now routinely used to detect HIV in suspected AIDS patients. It is being used to detect mutations in genes in suspected cancer patients too. It is powerful technique to identify many other genetic disorder.

ELISA is based on the principle of antigen-antibody interaction. Infection by pathogen can be detected by the presence of antigens (proteins, glycoproteins) or by detecting the antibodies synthesised against the pathogen. Hybridoma technology is also used to produce monoclonal antibody to detect microscopic pathogens.