Applicability of GLI 2012 Spirometry Equation and a Regional Equation Among Iraqi Adults

Spirometry is an essential tool to effectively diagnose and manage respiratory diseases. However, population-specific predicted values are essential to interpret the results accurately. The GLI-2012 equations were formulated to be used globally and are widely endorsed. However, these equations have never been validated among the Iraqi population. Pulmonary function tests were successfully performed by 738 (345 females) healthy, non-smoker, Iraqi adults. z-scores, per cent predicted values and frequency of measures below lower limit of normal (LLN) were computed using Global Lung Function Initiative (GLI) 2012 equations for Caucasians (GLI-C) and other or mixed (GLI-O) and Al-Qerem et al. equations. The Al-Qerem et al. equation produced the closest z-scores’ means to zero in forced vital capacity (FVC) in females (0.18) and in forced expiratory volume in 1 second (FEV1)/FVC% in both sexes (0.18 for males and 0.58 for females). For FEV1, the closest z-scores’ means to zero were produced by GLI-C (–0.15 for males and –0.18 for females). All the studied equations had a frequency of participants with LLN significantly different from the expected 5 per cent in at least one spirometric parameter. The GLI 2012 equations were not a suitable fit for Iraqi adults.