Chemiluminescent Immunoassay (CLIA)
Definition
A non-radioactive immunoassay that uses enzyme-catalysed chemiluminescent reactions to generate the detection signal. CLIA instruments measure light output in relative light units. It achieves sensitivity comparable to RIA in most clinical and forensic applications, without the regulatory and disposal requirements of radioactive materials. CLIA is the current dominant format on automated immunoassay analysers.
- Signal
- Enzyme-catalysed chemiluminescent reaction
- Measured as
- Relative light units
- Sensitivity vs RIA
- Comparable in most applications
- Advantage over RIA
- No radioactive material, no disposal regulation
- Status
- Dominant format on automated analysers
Common questions
Why did CLIA replace radioimmunoassay in most forensic and clinical labs?+
CLIA achieves similar sensitivity to RIA without requiring a licensed radioactive materials programme, specialised waste disposal, or a limited-shelf-life radiolabelled reagent, which made it far cheaper and simpler to run on high-throughput automated platforms.
What does CLIA output need to be paired with for forensic reporting?+
Like other immunoassay screens, a CLIA result is presumptive. A positive screen for a drug class must still be confirmed by a chromatographic-mass spectrometric method before being reported as an identification.
Related terms
- Calibration Curve
- In RIA, a set of standards containing known concentrations of unlabelled analyte that are run alongside test samples. Bound radioactivity is measured...
- Competitive Binding Assay
- An immunoassay format in which labelled and unlabelled forms of the same analyte compete for a fixed, limiting number of antibody binding...
- Cross-Reactivity
- The capacity of an antibody raised against one analyte to bind structurally related compounds. In RIA, cross-reactivity is the main driver of...
- Iodine-125 (125I)
- The radioisotope most commonly used in RIA. It emits gamma radiation, has a half-life of approximately 60 days, and can be covalently...
- Tritium (3H)
- A radioactive hydrogen isotope used as an alternative label in RIA, particularly for small organic molecules such as steroids and drugs where...