Role of whole-blood interferon-gamma release assay in the diagnosis of smear-negative tuberculosis
Abstract:SETTING: Hong Kong Chest Clinics.
OBJECTIVES AND METHODS: To conduct a prospective study investigating the role of a whole-blood interferon-gamma release assay, QuantiFERON®-TB Gold In-Tube (QFT-GIT), in the diagnosis of smear-negative tuberculosis (TB). The QFT-GIT result was compared with the final confirmed diagnosis after 12 months.
RESULTS: Of 262 smear-negative subjects, 188 had active TB, 167 (88.8%) of whom were QFT-GIT-positive; 74 had inactive/non-TB, 30 (40.5%) of whom were QFT-GIT-negative. The positive (PPV) and negative predictive values for active TB were respectively 79.1% and 58.8%. For this target group with high TB prevalence (71.8%), a positive test increased the chance of active disease by only 7.3%. Despite a positive likelihood ratio (LR) of 1.49, the negative LR was 0.28, making the diagnosis of active TB much less likely after a negative test. Although sensitivity and specificity showed no difference across different age groups, the PPV decreased (P < 0.001) with increasing age, likely reflecting the increased prevalence of competing diagnoses.
CONCLUSION: In an area with a high prevalence of latent TB infection, a positive QFT-GIT test does not add much to confirm the diagnosis of smear-negative TB, while a negative test indicates a need for further investigation.
Document Type: Regular Paper
Affiliations: 1: Tuberculosis and Chest Service, Centre for Health Protection, Department of Health, Hong Kong, China 2: Tuberculosis Reference Laboratory, Public Health Laboratory Centre, Centre for Health Protection, Hong Kong, China 3: Tuberculosis and Chest Unit, Grantham Hospital, Hong Kong, Special Administrative Region, China
Publication date: December 1, 2010
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