Do the 2012 spirometric Global Lung Function Initiative equations accurately diagnose restriction in the extreme obese

Background: Extreme obesity (“super” (S) and “super-super” (SS) obesity (O): body mass index 50-59.9 and ≥ 60 kg/m2 for SO and SSO, respectively) has been progressively recognised as a major public health concern worldwide. It remains unknown, however, whether the 2012 Global Lung Function Initiative (GLI) equations for spirometry can reliably identify obesity-related restriction in this population. Methods: We reviewed basic and advanced pulmonary function tests of 182 extreme-obese subjects (91 SO, 130 females, aged 18 to 79) who were free of major chronic cardiorespiratory disease known to induce restriction or chronic obstructive pulmonary disease. Results: Fifty-six subjects (~30%) presented with restriction (total lung capacity (TLC) 0.05). Conclusion: The GLI-2012 prediction equations for spirometry can reliably rule out restriction in the extreme obese. However, a reduced FVC should not be considered indicative of restriction unless confirmed by body plethysmography. Spirometric reference values for the extreme obese are warranted.