Assessment of Preserved Ratio Impaired Spirometry (PRISm) Based on Different Definitions in the Early COPD Cohort

Preserved ratio impaired spirometry (PRISm), which identifies a population at high risk for COPD, has drawn increasing attention. However, definitions for PRISm vary across studies, and researches comparing these definitions are limited.

We aim to assess the agreement, the clinical features, and the prevalence of PRISm defined by restrictive spirometric pattern (RSP) method [that is forced vital capacity (FVC) method] versus forced expiratory volume in the first second (FEV₁) method and by fixed values versus the lower limit of normal (LLN).

All 1862 participants from the ECOPD study underwent questionnaire investigation, spirometry, biphasic CT, and impulse oscillometry. Participants were categorized into control and two targeted groups (RSP fixed and PRISm fixed excluding RSP fixed) based on FVC and FEV₁ fixed definitions. Similar categorizations were conducted for RSP LLN versus PRISm LLN and PRISm fixed versus PRISm LLN. We assessed the agreement, the clinical features, and the prevalence of PRISm among these various definitions, repeating all analyses using Global Lung function Initiative (GLI) equation.

Significant overlap with merely moderate agreement (Kappa coefficient = 0.706, P value <0.001) existed between RSP fixed and PRISm fixed definitions. Participants identified as PRISm by both definitions exhibited lower lung function, higher airway reactance, and increased airway resistance compared to the control group. Similar findings were observed in RSP LLN versus PRISm LLN and PRISm fixed versus PRISm LLN. Our sensitivity analysis verified the consistency of these results. Furthermore, the prevalence of PRISm varied from 2.0% to 12.5% depending on the definitions and predicted equations, with the Chinese equation, LLN definition in Chinese equation and fixed definition in GLI equation yielding higher prevalence rates.

Our findings highlight concerns about the comparability of studies and the interchangeability of various definitions and reference equations for PRISm.