Why can’t I see a predicted flow-volume curve and its variability when selecting the Quanjer GLI-2012 equations?

Several manufacturers and their clientele have enquired about the lack of a predicted shape of the flow-volume curve and the normal scatter when using the GLI-2012 equations. Since data on PEF and other instantaneous flows were not collected for the GLI-2012, it is not possible for manufacturers to depict such predicted contours or a representative flow-volume curve using GLI-2012 prediction equations. The degree of imprecision that is inherent in producing such ‘ideal’ contours is so high that we recommend they should not be shown, focus instead being placed on the actual results. By presenting spirometry results in the form of a pictogram, the clinician, technician, physiologist and patient should all be able to interpret results far more accurately than previously, negating the need for any idealised (and often incorrect) flow-volume loop. We will, however, develop a set of curves with different diagnostic features to assist interpretation with respect to the shape of such curves, which will be posted on the website as part of the educational material currently being developed.

If, however, the manufacturer feels the need to continue to depict idealised curves, we suggest continuing to use prediction equations that were hitherto used.