Interpretation of IGRA test results:
Positive: M. tuberculosis infection is likely.
Negative: M. tuberculosis infection is unlikely, but cannot be excluded (especially if a patient is at high risk or has symptoms)
Indeterminate (QFT only) or Invalid (T-Spot only): The test did not provide enough information. Indeterminate and Invalid results indicate the test should be recollected for repeat testing.
Note
Indeterminate or Invalid results may be due to:
- low lymphocyte count, reduced lymphocyte activity, or inability of the patient's cells to release IFN-g. (Immune status factors.)
- nonspecific IFN-g circulating in the patient's blood or to the presence of heterophile effects.
- occurrence in patients with very low CD4 counts.
- preanalytic, analytic, or postanalytic errors (technical factors).
Borderline or Equivocal (T-Spot only): Borderline results indicate the test result is valid but should be repeated with a new specimen. A TST may also be useful in this case.
