IGRA Interpretation: QuantiFERON/T-SPOT results do not differentiate between Latent and Active TB. Requires clinical correlation.
Select Lab Result
Note: IGRA is preferred for BCG-vaccinated patients and those unlikely to return for TST reading.
Guidelines & Evidence
Clinical Details
Section 1
Results
Positive
Indicates infection. Follow-up with clinical assessment and CXR to rule out active disease.
Negative
LTBI unlikely. Note: False negatives can occur in severe immunosuppression or early after exposure (<8 weeks).
Indeterminate / Borderline
["High Nil: Background IFN-γ too high (recent illness, technical error).","Low Mitogen: Poor immune response (immunosuppression).","Action: Repeat test or perform TST."]
Section 2
IGRA vs TST
Advantages of IGRA
["No BCG Interference: Does not react to BCG vaccine (unlike TST).","Single Visit: No need for reading at 48-72h.","High Specificity: Better for screening BCG-vaccinated populations."]
