Why calibration is not required for the diffusion analyzer

For calculation of the results of a DLco measurement, only use the ratios of expired to inspired gas concentrations are relevant. Hence not the accuracy of absolute concentration reading is relevant, just the linearity of the gas analyzer. The gas analyzer measures both inspiratory and expiratory concentration online and can determine this ratio accurately.

Also according to the latest ATS/ERS guidelines for CO Diffusion with rapid gas analyzers, only regular biological controls and linearity checks with a 3l-syringe are necessary to ensure, that linearity of the gas analyzer is still within the range.