What Is Preserved Ratio Impaired Spirometry?

Preserved ratio impaired spirometry (PRISm) occurs when a patient has a normal ratio of forced expiratory volume in 1 second to forced vital capacity (FEV₁:FVC ≥0.70) but FEV₁ is less than 80% of predicted. When lung volumes are checked, some such patients have restrictive lung disease with total lung capacity <70% of predicted, but most have normal total lung capacity. Clinicians are left wondering what this means.

Researchers analyzed nine general U.S. population cohorts, with 53,701 adults who underwent spirometry. Lung volumes and bronchodilator reversibility data were not available. The prevalence of PRISm was 8.5%, obstructive spirometry (FEV₁:FVC <0.7) was seen in 17.6% of patients, and spirometry was normal in 73.9%. Patients who wer…