Facing the noise: Addressing the endemic variability in D _LCO testing

Single-breath diffusing capacity of the lung for carbon monoxide (D _LCO) is a common pulmonary function test that measures the ability of the lung to exchange gas across the alveolar-capillary interface. D _LCO testing is used to narrow the differential diagnosis of obstructive and restrictive lung disease, to aid in disability and transplant assessment, and to monitor medication toxicity. The variability in the measurement limits the utility of the test. Variability is attributable to differences in equipment, testing conditions, patient factors, and reference equations. Laboratories can minimize variability by ensuring that equipment meets recommended standards, implementing effective quality control programs, standardizing testing conditions and testing procedures, and accounting for pertinent patient characteristics.