Peak flow meter is a sensitive test for assessing airflow limitation in patients with respiratory symptoms suggestive of asthma in primary health care in Brazil

The peak flow meter is considered a complementary tool to spirometry for monitoring obstructive lung diseases. In many countries, spirometry is not easily accessible for diagnosing asthma in primary care. In this context, there has been growing interest in evaluating the role of the peak expiratory flow meter (PEFM) for asthma management, particularly in primary care settings. This study aims to assess the usefulness of PEFM in detecting airflow limitation (AFL), as identified by conventional spirometry, in a primary health care (PHC) setting in Brazil. This cross-sectional study was nested within a clinical trial. Participants aged 6 to 65, both sexes, with a history of respiratory symptoms suggestive of asthma and uncontrolled disease, from 28 PHC centers across all macroregions of Brazil were included. AFL was defined by spirometry according to international criteria and by PEFM when PEF was < 80% of the predicted value. The Global Lung Function Initiative (GLI) equations were used for parameterization. The accuracy of PEFM in detecting AFL, as identified by spirometry, was analyzed, and sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and area under the ROC curve (AUC) were reported. Among 298 participants, 107 (36%) had a confirmed asthma diagnosis. Spirometry identified AFL in 36% (n = 107) of participants, while PEFM detected AFL in 64.8% (n = 193). PEFM demonstrated an overall sensitivity of 82.4% (95% CI: 78.0%–86.7%) for detecting AFL compared with spirometry. Specificity was 44.4% (95% CI: 38.8%–50.0%), and AUC for the PEFM was 0.73. The Intraclass Correlation Coefficient (ICC) for absolute PEFM values was 0.01 (95% CI: -0.18 to 0.20, p = 0.473). The PEFM demonstrates high sensitivity for AFL, but it should be used with caution as a stand-alone tool for asthma diagnosis. Given its low cost and easy access in PHC settings, PEFM seems to be a useful initial screening tool for AFL, especially in resource-limited settings.