Interferon gamma release assay (IGRA)

An interferon-gamma release assay (IGRA) is a blood test that detects immune sensitization to Mycobacterium tuberculosis by measuring interferon-gamma released by T cells after exposure to TB-specific antigens. It helps identify latent or active TB infection, is more specific than the tuberculin skin test and unaffected by BCG vaccination, but cannot alone distinguish latent from active disease and needs clinical follow-up.

The IGRA (interferon‑gamma release assay) is a blood test that detects immune sensitization to Mycobacterium tuberculosis. It measures interferon‑gamma released by T cells after exposure to TB‑specific antigens, helping identify latent TB infection and support tuberculosis screening, especially in people vaccinated with BCG. It cannot reliably distinguish latent from active TB and must be interpreted with clinical assessment and other tests.

India prohibited IGRA tests because they perform inconsistently in high TB-burden settings: poor sensitivity and predictive value, inability to distinguish latent infection from active disease, and risk of false negatives or positives that can delay or misdirect treatment. High cost and limited added benefit over established diagnostics (sputum microscopy/GeneXpert) led authorities to advise against routine use for diagnosing or screening TB.

A positive IGRA means you likely have been infected with Mycobacterium tuberculosis but does not distinguish latent from active disease. Next steps: clinical assessment (symptom review), chest X‑ray and sputum tests if symptomatic to rule out active TB. If active TB, start full multi‑drug treatment and public health measures; if latent TB, consider preventive therapy to lower the risk of progression, especially if immunosuppressed.

IGRA test costs vary by country and provider. In the United States it commonly ranges about $50–$200; in the United Kingdom private testing is roughly £80–£150 (NHS testing is free for eligible patients); in India typical private-lab prices are about ₹2,000–₹3,500. Prices depend on lab, clinic, and insurance or public-health coverage—check the testing facility for exact fees.

If you test positive for TB, your clinician will order further tests (chest X‑ray and sputum samples) to determine active versus latent infection. Active TB requires multi‑drug treatment—usually a six‑month regimen—plus isolation until noninfectious and public‑health notification/contact screening. Latent TB is treated with preventive therapy to reduce progression risk. Regular follow‑up monitors treatment response and medication side effects.