Overview
IGRAs incubate whole blood or PBMCs with ESAT-6/CFP-10 peptides and measure interferon-γ as evidence of T-cell sensitization to M. tuberculosis complex antigens.
Clinical Importance
Screen for latent TB infection, especially in BCG-vaccinated persons where TST specificity is reduced
TB infection testing before immunosuppression in selected pathways
Specimen Requirements
- Specimen: whole blood collected in manufacturer-specific tubes (QuantiFERON) or lithium heparin for T-SPOT per kit
- Handling: mix tubes correctly; incubate within validated time windows; do not refrigerate before incubation unless kit allows
- Stability: strict timing; delayed incubation invalidates many IGRA collections
Analytical Method
Antigen, nil, and mitogen controls are incubated; IFN-γ is measured by ELISA (QuantiFERON) or enumerated as spots (T-SPOT). Results: positive, negative, or indeterminate based on kit algorithms.
Instruments Used
Automated analyzers
- ELISA processors for QuantiFERON IFN-γ measurement
- Automated immunoassay platforms validated for IGRA readouts
- ELISPOT readers for T-SPOT
Manual methods
- Manual ELISA and ELISPOT workflows per manufacturer
Reference Values
Assay cutoffs, units, and reference intervals are method- and manufacturer-specific. Always interpret against the performing laboratory report (CLSI EP28-A3c for quantitative intervals where applicable). Serologic patterns require clinical correlation and current guideline algorithms (WHO/CDC/society guidance as adopted locally).
Interpretation is categorical per manufacturer algorithm (not a traditional reference interval). Indeterminate results require clinical review and often repeat.
Interpretation
Common Causes of Increased Results
- Positive IGRA . M. tuberculosis infection (latent or active) possible; does not distinguish latent vs active TB
Common Causes of Decreased Results
- Negative IGRA; lower likelihood of infection; false negatives possible in immunocompromise
- Indeterminate; failed mitogen or high nil; repeat/investigate immune status
Clinical Significance
- Latent TB infection screening
- Pre-biologic/immunosuppression TB risk assessment
Factors Affecting Results
Pre-analytical
- Incorrect tube filling/mixing
- Incubation delay beyond kit limits
Analytical
- ELISA technical errors
- Borderline values near cutoffs
Post-analytical
- Using IGRA alone to diagnose active TB
Advantages and Limitations
Advantages
- Not confounded by BCG vaccination like TST
- Single visit blood test
Limitations
- Cannot separate latent from active TB
- Indeterminates in immunocompromised patients
- Cost and strict preanalytics
Clinical Pearls
IGRA positive means immunology remembers TB antigens; chest imaging and clinical exam decide latent vs active.
References
Authoritative textbooks, guidelines, and reviews supporting this laboratory test reference. Verify reference intervals, critical limits, and method details against institutional protocols and current guideline editions.
Textbooks
- McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods (verify current edition). Chapters on clinical immunology and serology.
- Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics (verify current edition). Immunoassay and protein chapters.
CLSI and Professional Guidelines
- Centers for Disease Control and Prevention. Laboratory testing recommendations for infectious disease serology and related algorithms (verify current CDC guidance for the pathogen).
- Clinical and Laboratory Standards Institute. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory. CLSI document EP28-A3c (verify current edition).
- Clinical and Laboratory Standards Institute. Immunoassay and related method evaluation documents (e.g., EP05, EP06, EP07, EP17; verify current editions relevant to the assay).
- College of American Pathologists. Accreditation and proficiency testing expectations for immunology/serology (verify current CAP checklist requirements).
- International Federation of Clinical Chemistry and Laboratory Medicine (IFCC). Recommendations relevant to protein and immunoassay measurands (verify current IFCC documents).
WHO Publications
- World Health Organization. Laboratory and diagnostic guidance for serologic and immunologic testing (verify current WHO publication for the analyte/assay).
Frequently Asked Questions
Common questions about using this Interferon-Gamma Release Assay (IGRA) laboratory test Medical Laboratory Library reference in Medical Laboratory Science education.
What is the Interferon-Gamma Release Assay (IGRA) laboratory test reference used for?
This Medical Laboratory Library page summarizes the clinical importance of Interferon-Gamma Release Assay (IGRA). Review the Clinical Importance section for why the test is ordered in laboratory medicine practice.
Where can I find Interferon-Gamma Release Assay (IGRA) specimen requirements?
See the Specimen Requirements section on this page for specimen information related to Interferon-Gamma Release Assay (IGRA). Confirm collection details against your laboratory protocol.
Where are Interferon-Gamma Release Assay (IGRA) reference values listed?
See the Reference Values section on this Laboratory Library page. Reference ranges can vary by method and population, so verify intervals with your laboratory.
How do I interpret Interferon-Gamma Release Assay (IGRA) results?
Use the Interpretation section for laboratory interpretation framing, including increased and decreased result patterns when provided. Do not treat educational text as a patient-specific diagnosis.
What analytical method is used for Interferon-Gamma Release Assay (IGRA)?
See the Analytical Method section for principle and method notes. Method details may differ by instrument and institutional SOP.
Are related laboratory tests linked from Interferon-Gamma Release Assay (IGRA)?
Yes. The Related Laboratory Tests section lists connected references for continued lookup in the Medical Laboratory Library.
How can I continue learning after reading Interferon-Gamma Release Assay (IGRA)?
Use Continue learning links on this page for related Academy lessons, medical laboratory quizzes, or laboratory case studies when available for this Immunology & Serology topic.
What are the clinical pearls for Interferon-Gamma Release Assay (IGRA)?
See the Clinical Pearls section for concise laboratory practice notes associated with Interferon-Gamma Release Assay (IGRA). Apply pearls alongside institutional protocols.
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