Table. 6—

Acceptable test criteria for diffusing capacity of the lung for carbon monoxide

Use of proper quality-controlled equipment
VI of >85% of largest VC in <4 s#
A stable calculated breath hold for 10±2 s. There should be no evidence of leaks, or Valsalva or Mueller manoeuvres
Expiration in <4 s (and sample collection time <3 s)#, with appropriate clearance of VD and proper sampling/analysis of alveolar gas
  • VI: inspired volume; VC: vital capacity; VD: dead space. #: tests outside these timing limits might still have clinical utility, but these deviations from standard acceptability criteria should be noted and possible impact/correction factors considered.