ELISA is stand for Enzyme-linked immunosorbent assay. It is an immunological or serological test to check antigen present in the serum. It have 2 types Direct ELISA or Sandwich ELISA Test and Indirect ELISA test. For Direct ELISA test, it is used to diagnose various microbial infections (such as HIV, Hepatitis A and C, Cholera Vibrio, Helicobacter pylori,...), cancer and other immunological disorders. Different from Direct ELISA, Indirect ELISA is used to diagnosed Hantavirus, rubella virus, toxoplasma.... Procedure of Sandwich ELISA Pour known antigen of specific antibodies on well containing micro titer plate and wait for 2-3 hours or over night then wash with buffer to remove unbound antibodies. Add patient serum specimen on the well and wait for 1-2 hours and then wash with buffer. Add Enzyme labelled (linked or conjugated) antibodies on the well and wash with buffer. Finally, add the substrate (colorless substance) on the well and wait for 1-2 hours to observe the react