Main idea: Nitric oxide levels are higher in allergic rhinitis, particularly when using high aspiration flows and in younger patients, who often perceive this condition as a source of disability.
Nasal nitric oxide (nNO) is considered a biomarker of nasal inflammation. The objective of the study was to perform a systematic review with meta-analysis and meta-regressions on the association between nitric oxide levels and allergic rhinitis (AR).
Results: Overall, 39 articles were included: 30 containing data on nitric oxide measured by nasal aspiration (1881 patients with allergic rhinitis and 1337 without allergic rhinitis) and 12 assessing nitric oxide by nasal exhalation (525 patients with allergic rhinitis and 350 controls). Compared with controls, allergic rhinitis presented significantly higher nitric oxide values both during nasal aspiration and nasal exhalation. Sensitivity and subgroup analyses confirmed that the results of the evaluated outcomes were not affected by the presence of clinical confounding factors (asthma, nasal polyps, inhaled corticosteroids, smoking history). It is valid for both perennial and seasonal diseases during exposure to allergens. For the aspiration method meta-regression indicated that older age and a better pulmonary function were associated with a lower difference in nitric oxide levels between patients with allergic rhinitis and controls, whereas an increasing aspiration flow was associated with a high effect size.