Can the measurement of pulmonary diffusing capacity for nitric oxide replace the measurement of pulmonary diffusing capacity for carbon monoxide?

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Pulmonary diffusing capacity for carbon monoxide (DLCO) has been an important pulmonary function test used since the 1950’s. It measures the uptake of CO from the alveolar space into pulmonary capillary blood, following the same path as oxygen. It’s used to evaluate/follow the progress of various lung diseases. In the eighties, a new test was developed similar to the DLCO test: pulmonary diffusing capacity for nitric oxide (DLNO). About 81–90% of the variance in DLNO is shared by DLCO in patients with cardiopulmonary disease and in healthy subjects. When DLNO is abnormally low, so is DLCO, and when DLNO is normal, so is DLCO (Kappa Statistic=0.69, n=251). The probability that DLNO and DLCO will be abnormally low when a cardiopulmonary disease is present (sensitivity) is 79% and 68%, respectively. The DLNO test avoids many technical issues associated with the measurement of DLCO: (1) DLNO is relatively unaffected by inspired oxygen concentration or ambient pressure, (2) DLNO is unaffected by carboxyhemoglobin, (3) DLNO is minimally affected by hemoglobin (Hb) concentration, thus correcting for Hb is not needed. (4) DLNO is more affected by lung volume compared to DLCO, thus DLNO divided by alveolar volume (KNO) is a better measure than KCO in those with restrictive lung disease, and (5) DLNO is a more stable measure over time compared to DLCO. Therefore, DLNO has several advantages over DLCO in the management of patients and could replace the DLCO test in most cases moving forward.