Abstract
Introduction: Interferon γ release assays (IGRAs) are used in the diagnosis of latent TB, but up to 6.1% yield an indeterminate test result (ITR; Diel Chest 2009). IGRAs are not currently used for diagnosis of active TB (Sester ERJ 2011). We determined the indications for T-Spot.TB and frequency of ITRs in our routine practice.
Methods: Patient records were reviewed for all T-Spot.TB tests performed in Glasgow (May 07 - June 08). Data was collected on patient demographics, clinical assessment, reasons for request and final diagnosis.
Results: T-Spot.TB was performed on 303 patients (see table 1). The rate of ITRs on first testing was 55/303 (18.2%). Almost half were performed for active TB (45%), and symptoms suggestive of active TB increased the likelihood of ITRs. Frequency of ITRs varied between hospital (2-34%) and specialty (0-40%) (data not shown). Female sex, Asian race, ex or non-smoking status, excess alcohol and age >75 favoured an ITR. Immunosuppressive drugs had no effect, although patients with ITR had a slightly lower lymphocyte count. Of the 26 tests repeated, 14 were negative, 6 positive and 6 ITR. Overall 35/303 (11.5%) of patients had an ITR. On follow up 31/35 had no TB, and 4/35 latent, presumed clinical or confirmed TB.
Conclusions: ITRs were more common than in other studies, and may be influenced by patient factors and system failures. Inappropriate testing was common and may be minimised by further educating staff requesting and performing tests.
- © 2011 ERS
