Low forced expiratory flow at 25-75% (FEF25-75%) can signal fixed airflow obstruction in patients with asthma, according to a study in the Journal of Asthma and Allergy. The researchers defined low FEF25-75% as a post-bronchodilator FEF25-75% z-score less than −0.8435, and fixed airflow obstruction as a post-bronchodilator forced expiratory volume in the first second (FEV₁)/forced vital capacity (FVC) z-score less than −1.645. An analysis of data for 312 patients with stable asthma on standard treatment found patients with low FEF25-75% and fixed airflow obstruction had lower FEV₁ z-scores and FEV1/FVC z-scores, as well as more pack-years, years of biomass and occupational exposure, higher Asthma Control Questionnaire-5 and Chronic Obstructive Pulmonary Disease Assessment Test scores, and more frequent exacerbations than patients with normal FEF25-75% without fixed airflow obstruction. Patients with low FEF25-75% without fixed airflow obstruction showed a similar trend but to a lesser extent. The researchers advised frequent follow-up for patients with low FEF25-75%.