Discuss briefly the process of indirect ELISA.

ELISA is short form for Enzyme Linked Immuno sorbent Assay.
* Indirect Elisa is a process that is used to detect antibodies. HIV test is an example for Indirect Elisa.
* In this method serum of a suspected patient is added to an antigen coated microtitre plate.
* Primary antibodies in the serum bind to the antigen.
* Enzyme linked secondary antibody is then added to this antigen antibody complex, followed by enzyme substrate.
* The resulting reaction between enzyme and enzyme substrate produces a colour change.
* The colour change is read by a spectrophotometer.
* If there is no change in the colour, the test result is negative. If there is change in the colour, the test result is positive.