ELISA test is used for the detection of
A) Antibodies
B) Viral disease
C) AIDS
D) All of the above

Hint: It is a laboratory test which detects antibodies in the blood.

Complete answer:
ELISA test is used to detect antibodies, viral diseases, and AIDS.
ELISA known as Enzyme-linked immunosorbent assay is used to measure the concentration of a compound (usually antibodies or antigens) in solution, used commonly in laboratories. Ag-Ab interaction is monitored by enzyme measurement. The principal to ELISA is similar to RadioImmunoAssay (RIA) but depends on an enzyme rather than a radioactive label. In this technique, various antigen-antibody combinations are used (where one must be enzyme-labeled either antigen or antibody), and enzyme activity is measured colorimetrically. For quantitative assessment, the enzyme activity is measured using a substrate that changes color when modified by the enzyme. Light absorption of the product formed after substrate addition is measured and converted to numeric values.ELISA is of four types:
- Direct ELISA
- Indirect ELISA
- Sandwich ELISA
- Competitive ELISA


Fig: Schematic diagram showing different types of ELISA

So, the correct answer is ‘All of the above’.

Note: A modification of the ELISA called ELISPOT (enzyme-linked immunospot assay) refers to ELISA-like capture and measurement of proteins secreted by cells. Proteins are plated in PVDF-membrane-backed microplate wells. It is a "sandwich" assay in which the proteins are captured on the surface as they are secreted by the cells in the plate, and detection is with a precipitating substrate. ELISPOT is similar to western blot in that the result is spots on a membrane surface.