The Development of Population-Specific Spirometric Reference Equations for Iraqi Adults

Background: Spirometry is one of the most important medical tests used to diagnose and monitor diseases affecting the respiratory system. There are several reference equations that can provide reference values to be referred to during the spirometer examination process. However, the equations of the Global Lung Function Initiative 2012 (GLI 2012) Committee were found not to apply to Iraqi populations. Furthermore, there is currently no equation derived from normal values specific to Iraqis. Objectives: The aim of this study was to establish a spirometric reference equation that can be used in the Iraqi population to diagnose and monitor respiratory diseases. Methods: Spirometry data were collected from healthy, non-smoking Iraqi adults. Generalized additive models of location, scale, and shape were used to construct the equations. Spirometry parameters, including predicted values, predicted percent, and Z-scores, were calculated based on the equations developed. A new spirometry dataset consisting of 344 participants, who were not involved in creating the equations, was used for equation validation. Results: The equations were constructed using spirometer data from 966 adults (33.1% women). The equations were evaluated by calculating Z-scores and predicted values, and the results showed that Z-scores for all variables calculated based on the present equation were less than ±0.5. Conclusions: To reduce the effect of ethnic and race on the normal values of spirometry parameters, the equations developed in this study can be used to evaluate and diagnose respiratory diseases in Iraqis.