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.