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

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

to assess the potential usefulness of measuring exhaled nitric oxide (eNO).

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.

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.

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.