The role of per cent predicted 6-min walk distance in pulmonary arterial hypertension

Absolute 6-min walk distance (6MWD) predicts mortality in pulmonary arterial hypertension (PAH), but varies greatly between normal individuals due to physiological factors such as age, sex, height and weight. The % predicted 6MWD adjusts for these factors and may predict mortality more reliably. The aim of the study was to compare the strength of mortality prediction by absolute and % predicted 6MWD in PAH at baseline and on treatment. % predicted 6MWD was calculated using four different reference equations in 137 PAH patients (idiopathic and connective tissue disease associated) diagnosed between November 2000 and November 2009. Cox proportional hazards and receiver-operating characteristic (ROC) analyses were used to compare the prognostic strength of absolute and % predicted 6MWD. % predicted 6MWD was predictive of all-cause mortality at baseline (hazard ratio 0.74-0.83 per 10% increase; p<0.05) and on treatment (0.67-0.75 per 10% increase; p<0.01), but each respective area under the ROC curve was not different from that of absolute 6MWD for predicting 2-yr mortality at baseline (absolute versus % predicted: 0.74 versus 0.71-0.75) or on treatment (0.77 versus 0.72-0.78). In conclusion, % predicted 6MWD may help clinicians interpret the 6-min walk test, but its prognostic value is not superior to that of absolute 6MWD.