Immunoassays: ELISA, CLIA and Ligand-Binding Methods

ELISA and CLIA immunoassay analyzer in the laboratory

Immunochemical (ligand-binding) analysis is based on the specific antigen-antibody reaction and is used to quantify substances present at extremely low concentrations: hormones, tumor markers, infectious disease markers, drugs and proteins. The two most common formats are the enzyme-linked immunosorbent assay (ELISA) and the chemiluminescent immunoassay (CLIA).

Principle of Ligand-Binding Assays

The method is based on highly specific binding of an antibody to an antigen (ligand). To detect the reaction, a label (an enzyme, a luminophore or a fluorophore) is attached to one of the components. The signal intensity is proportional to the analyte concentration.

Main formats:

ELISA: enzyme label, color reaction, photometric measurement
CLIA: chemiluminescent label, light emission measurement, high sensitivity
FIA: fluorescent label
Immunochromatography: rapid tests (POCT)

Reaction Formats

Format	Principle	Application
Sandwich	Two antibodies "sandwich" the antigen	Large molecules (hormones, proteins)
Competitive	The analyte competes with a labeled antigen	Small molecules (steroids, drugs)
Indirect	Detection of antibodies in the sample	Infectious disease serology

Clinical Applications

Endocrinology: thyroid hormones, cortisol, insulin, reproductive hormones
Tumor markers: PSA, CA-125, CEA, AFP
Infectious disease serology: hepatitis, HIV, TORCH
Cardiac markers: troponins, BNP/NT-proBNP
Therapeutic drug monitoring: drug concentrations

In large laboratories, CLIA is gradually replacing classic ELISA thanks to its higher sensitivity, wider dynamic range and full automation on closed-system analyzers.

Frequently Asked Questions

How is CLIA better than ELISA?

CLIA offers higher sensitivity, a wider dynamic range and full automation, whereas ELISA is simpler and cheaper for small volumes.

What is the sandwich method?

A format in which the antigen is bound between two antibodies. It is used for large molecules and provides high specificity.

Can antibodies be detected?

Yes, the indirect format is used for serological diagnosis of infections: it detects the patient's antibodies to the pathogen.

Choosing an Immunoassay Analyzer

KombiMED GmbH is an independent partner for procurement and market access for laboratory equipment from Europe. We will help you choose an immunoassay analyzer (ELISA/CLIA) that matches your laboratory's tasks and volume, and we provide delivery, commissioning and staff training.

See also:

Analytical Methods in Clinical Chemistry: an overview
Flow Cytometry in Clinical Diagnostics
Immunoturbidimetry and Nephelometry for Protein Analysis
Contact KombiMED: equipment selection