Pattern of diffusion disturbance related to clinical diagnosis: The KCO has no diagnostic value next to the DLCO

SummaryAim of the studyThe diffusion capacity of the lung for carbon monoxide (DLCO) is an important tool in the diagnosis and follow-up of patients with pulmonary diseases. In case of a decreased DLCO the KCO, defined as DLCO/VA (VA is alveolar volume), can differentiate between normal alveolocapillary membrane (normal KCO) and abnormal alveolocapillary membrane (low KCO). The latter category consists of decreased surface of the membrane, increased thickness or decreased perfusion of ventilated alveoli. The VA/TLC (TLC is total lung capacity determined by whole body plethysmography) can partially differentiate between these categories. The aim of this study was to investigate the diagnostic value of the specific diffusion disturbances, which can be constructed by combining the DLCO, KCO and VA/TLC.MethodsIn 460 patients the diagnosis made by clinicians were fitted into five diagnostic categories: asthma, chronic obstructive pulmonary disease (COPD), treatment effects of haematologic malignancies, heart failure and diffuse parenchymal lung diseases (DPLD). These categories were linked to the pattern of diffusion disturbance.ResultsAlmost all patients with asthma have a normal DLCO, most patients in the other groups do not have the expected pattern of diffusion disturbance, especially in the group with DPLD a bad match is observed.ConclusionIn this study the pattern of diffusion disturbance is of limited use in establishing a diagnosis. The use of the KCO next to the DLCO has no additional diagnostic value. Regional ventilation–perfusion inequality probably forms an important underlying mechanism of decreased DLCO.