Patient eligibility for anti-fibrotic therapy in idiopathic pulmonary fibrosis can be altered by use of different sets of reference values for calculation of FVC percent predicted.

Antifibrotic drugs for idiopathic pulmonary fibrosis patients in England and Scotland are only available to those with FVC percent predicted (FVC%pred) less than or equal to 80%. The prescribing guidance does not state which set of reference values should be used and we show that a patient's FVC%pred can change by 4-6% depending on the choice of reference. We calculated FVC%pred for a group of 528 IPF patients using three different sets of reference values. 90% of patients with FVC%pred 80-85% calculated using European Community Coal and Steel (ECSC) reference values fall into the eligible range when NHANES reference values are used.