Abnormality on pulmonary function testing Abnormal KCO 2020-12-23T12:36:28Z Any deviation from the normal range of KCO. The KCO is a measurement of the rate constant for alveolar uptake of CO during breath-holding in the single breath measurement of DLCO at full inflation. The DLCO is derived as the product of the KCO and the single breath alveolar volume (VA) divided by PB-PH2O. The carbon monoxide transfer coefficient (KCO is approximately kCO/barometric pressure in mL/minute/ mmHg/L) is often written as DLCO/VA. It is an index of the efficiency of alveolar transfer of carbon monoxide.