Measurement of exhaled nitric oxide as a potential screening tool for pulmonary tuberculosis

BACKGROUND: There is a need for low-technology, inexpensive screening tools for active tuberculosis (TB) case finding.

OBJECTIVE: To assess the potential usefulness of measuring exhaled nitric oxide (eNO).

DESIGN: Cross-sectional comparison in Hanoi, Viet Nam, comparing 90 consecutive smear-positive, culture-confirmed TB patients presenting at a referral hospital with office workers (no X-ray confirming TB) at this hospital (n = 52) and at a construction firm (n = 84). eNO levels were analysed using a validated handheld analyser.

RESULTS: eNO levels among TB patients (median 15 parts per billion [ppb], interquartile range [IQR] 10–20) were equal to those among construction firm workers (15 ppb, IQR 12–19, P = 0.517) but higher than those among hospital workers (8.5 ppb, IQR 5–12.5, P < 0.001). Taking the hospital workers as the comparison group, best performance as a diagnostic tool was at a cut-off of 10 ppb, with sensitivity 78% (95%CI 68–86) and specificity 62% (95%CI 47–75). Test characteristics could be optimised to 84% vs. 67% by excluding individuals who had recently smoked or consumed alcohol.

CONCLUSION: While eNO measurement has limited value in the direct diagnosis of pulmonary TB, it may be worth developing and evaluating as a cost-effective replacement of chest X-ray in screening algorithms of pulmonary TB where X-ray is not available.