Nitric oxide measurement levels greater than 20 ppb are indicative of an acute asthma attack with airway hyperreactivity. Clinical nitric oxide measurements primarily reflect the state of the eosinophil inflammatory response present in the airways of patients with bronchial asthma. Nitric oxide is produced directly by the cells involved in bronchial asthma, and the concentration is highly correlated with the number of eosinophils, serving as a relatively sensitive marker of airway hyperresponsiveness and chronic inflammation. The more pronounced the inflammatory response of the airways resulting in a hyperreactive state, the higher the concentration of nitric oxide, which is often used in conjunction with bronchial excitation tests and bronchodilatation tests to clarify the final diagnosis of asthma.