[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Biochemistry](https://durgical.com/en/biochemistry/) › ELISA (enzyme-linked immunosorbent assay)

[Biochemistry](https://durgical.com/en/biochemistry/) · Topic

# ELISA (enzyme-linked immunosorbent assay)

ELISA detects and measures antibodies or antigens in a sample using an enzyme that makes colour when the antibody binds its target.

Updated 2026-11-01

## Key facts

- Antigen or antibody is fixed to a plate; the sample is added and washed; an enzyme-linked secondary antibody (peroxidase, alkaline phosphatase) makes colour with its substrate.
- Colour intensity is proportional to the amount of what is being measured (read in a spectrophotometer).
- Indirect: looks for the patient's antibodies (e.g. anti-HIV). Sandwich: looks for antigens (e.g. p24 antigen, dengue NS1). Competitive: small molecules.
- It is very sensitive: ideal for screening. A reactive result is confirmed with another test.
- It is a protein (immunology) technique, not a nucleic acid one.

## In detail

- Indirect ELISA steps: coat the plate with antigen → block → patient serum → wash → enzyme-labelled anti-human IgG → wash → substrate → read.
- Sandwich ELISA uses two antibodies against the same antigen: one captures it on the plate and the other, labelled, detects it.
- Fourth-generation HIV tests combine antibodies and p24 antigen, which shortens the window period.
- Chemiluminescence immunoassays work the same way, but the signal is light instead of colour.
- Lateral-flow rapid tests (cassettes) are a simplified version of the same principle.

**Also called**
Enzyme immunoassay (EIA)

## Clinical notes

- Screening for HIV, hepatitis B and C and syphilis in blood banks and prenatal care.
- In dengue: NS1 antigen in the first days of fever and IgM after day five.
- Measuring hormones, tumour markers and autoantibodies in the clinical laboratory.

## Related conditions

- [HIV infection and AIDS](https://durgical.com/en/conditions/hiv-infection-and-aids/)
- [Dengue](https://durgical.com/en/conditions/dengue/)
- [Viral hepatitis](https://durgical.com/en/conditions/viral-hepatitis/)

## Related

- [Southern, Northern and Western blots](https://durgical.com/en/biochemistry/topics/southern-northern-and-western-blots/)
- [Polymerase chain reaction (PCR)](https://durgical.com/en/biochemistry/topics/polymerase-chain-reaction/)

## Test yourself

Think of the answer, then tap the question to see it.

## Which type of ELISA detects viral antigens such as dengue NS1?

Sandwich ELISA: one antibody captures the antigen on the plate and another, enzyme-labelled, detects it.

## Why does a reactive HIV ELISA need a confirmatory test?

It is very sensitive but can give false positives; it is confirmed with a more specific test.

## What creates the measurable signal in an ELISA?

The enzyme on the detection antibody, which turns a colourless substrate into a coloured product.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/biochemistry/topics/elisa/)

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [ELISA blood test: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003332.htm) (MedlinePlus, US National Library of Medicine, 2026); [Screening and diagnosis for HIV: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003538.htm) (MedlinePlus, US National Library of Medicine, 2026); [Dengue Fever Test: MedlinePlus Medical Test](https://medlineplus.gov/lab-tests/dengue-fever-test/) (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

[← All of biochemistry](https://durgical.com/en/biochemistry/)

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/biochemistry/topics/elisa/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/topics/elisa/