FEV1n

FEV1n is a term used in some pulmonary function literature to denote a normalized or adjusted value of the forced expiratory volume in one second (FEV1). It is not universally standardized; in practice, FEV1n typically refers to the measured FEV1 expressed relative to a reference value that accounts for key demographic and anthropometric factors such as age, sex, height, and ethnicity. Two common ways to express this normalization are as a percent of predicted FEV1 or as a z-score relative to the reference population.

Calculation: FEV1n as percent predicted = (FEV1 / FEV1_predicted) × 100. FEV1n as a z-score = (FEV1 − FEV1_predicted) / SD_predicted, where predicted values and their standard deviation come from established reference equations (for example GLI or other population-based references).

Interpretation and use: FEV1n is used to compare an individual's lung function against a matched reference population and to monitor changes over time or in response to treatment. Clinically, lower FEV1n indicates reduced airway function consistent with obstruction, while higher values indicate better function. In many guidelines, FEV1 percent predicted is the standard metric; FEV1n (especially as a z-score) is frequently used in research and pediatric practice to adjust for growth and development.

Limitations: FEV1n depends on the reference equations selected and the demographic characteristics included, and different laboratories may use different standards. Measurement quality, device calibration, and patient effort also affect FEV1. Because the term is not universally standardized, it is important to consult the methods section of a study to understand how FEV1n is defined and calculated.