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Indeterminate IGRA — SCE Infectious Diseases MCQ

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EasyTuberculosisIndeterminate IGRASCE Infectious Diseases

A 45-year-old man with Crohn disease on Infliximab is screened for latent TB before treatment. His IGRA is indeterminate. Chest X-ray is normal. He is asymptomatic. What does an indeterminate IGRA result mean?

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Correct answer: D — The test did not produce a valid result — the positive control (mitogen) failed, usually due to immunosuppression or poor sample handling; the test should be repeated or Mantoux test used as an alternative

An indeterminate IGRA result means the test is invalid — the mitogen (positive control) tube failed to produce an adequate response. This most commonly occurs in immunosuppressed patients (whose lymphocytes cannot mount an IFN-gamma response to any antigen, including the positive control). It can also result from technical issues (sample handling errors). Management: repeat the IGRA (may still be indeterminate in immunosuppressed), perform a Mantoux test as an alternative, or — if both are unreliable — make a clinical decision about latent TB treatment based on risk assessment (country of origin, exposure history).

Reference: NICE NG33 2016 – TB; UKHSA 2024 – IGRA guidance