Regarding Chemiluminescent assays, which statement is true?

Appeared in: AIIMS CRE, SNO-2024

Explanation

Chemiluminescent immunoassays (CLIA) use an enzyme label to trigger a light-producing chemical reaction.
Alkaline phosphatase (ALP) is a commonly used enzyme catalyst in CLIA, along with horseradish peroxidase (HRP).
The enzyme cleaves a chemiluminescent substrate, causing it to emit photons of light, which are then measured.
The amount of light produced is directly proportional to the concentration of the analyte being measured.

Option A: This statement is incorrect. CLIA uses light-emitting chemical reactions for detection. The use of radioactive isotopes is the defining characteristic of Radioimmunoassay (RIA).
Option C: This is incorrect. The light produced in a CLIA reaction is measured automatically by a sensitive instrument called a luminometer, which uses a photomultiplier tube. It does not involve manual observation in a darkroom.
Option D: This statement is incorrect. A major advantage of CLIA is its superior sensitivity compared to conventional colorimetric ELISA. It can detect analytes in the femtogram range.

Visual 1: Diagram: A flowchart illustrating the principle of a sandwich CLIA, showing the capture antibody, antigen, enzyme-labeled detection antibody, addition of substrate, and subsequent light emission measured by a luminometer.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Principles of Chemiluminescent Immunoassays (CLIA) as background academic context rather than a clinical decision trigger.
CLIA is a cornerstone of modern clinical diagnostics, used for quantifying hormones (e.g., thyroid hormones), vitamins (e.g., Vitamin D), tumor markers (e.g., PSA), and infectious disease markers (e.g., HIV, Hepatitis).
Nurses should understand that the high sensitivity of CLIA allows for earlier detection and more precise monitoring of diseases compared to older methods.
What if a test required detecting an extremely low level of a hormone? CLIA would be preferred over ELISA due to its higher sensitivity and wider dynamic range, providing a more accurate result.

How to Approach the Question

This is a factual recall question that asks you to identify the true statement about a specific laboratory technique.
First, identify the core subject: Chemiluminescent assays (CLIA).
Systematically evaluate each option based on your knowledge of immunoassays.
Eliminate options that describe other techniques. For example, 'radioactive isotopes' points to RIA, not CLIA.
Compare the features of CLIA to similar techniques like ELISA to assess claims about sensitivity.
Select the option that accurately describes a fundamental component or principle of CLIA, such as the role of catalytic enzymes.

Concept Tested & Keywords

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Practise the full AIIMS CRE, SNO-2024

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