This proficiency test is the fourth one carried out by the Physical Test Methods (PTM) Sub-Group to assess the capability of the participating laboratories to measure diffusion capacity using the CORESTA Recommended Method (CRM) No. 77 as a general guideline.

The results from this study serve as a check that laboratory procedures and their development over time did not lead to a substantial increase in between-laboratory variability and it further offers each laboratory the possibility of assessing its performance in comparison with other laboratories and to derive actions for improvement.

The robust coefficient of variation for measurements on LIP bands did not change substantially over all the four proficiency tests. This study did not show any significant difference in mean values and variability obtained with instruments from different manufacturers.

The Sub-Group recommendation was to carry out further proficiency tests on a regular basis to ensure that laboratories do not drift apart and that the between-laboratory variability does not increase over time. It was also recommended to continue attempts to identify a reference material and develop a ‘gold-standard’ method based on CRM 77 that can be used to assign values to calibration or reference standards.