Combined measurement of carbon monoxide and nitric oxide lung transfer does not improve the identification of pulmonary hypertension in systemic sclerosis

Screening is important to determine whether patients with systemic sclerosis (SSc) have pulmonary hypertension because earlier pulmonary hypertension treatment can improve survival in these patients. Although decreased transfer factor of the lung for carbon monoxide ( T LCO ) is currently considered the best pulmonary function test for screening for pulmonary hypertension in SSc, small series have suggested that partitioning T LCO into membrane conductance (diffusing capacity) for carbon monoxide ( D MCO ) and alveolar capillary blood volume ( V C ) through combined measurement of T LCO and transfer factor of the lung for nitric oxide ( T LNO ) is more effective to identify pulmonary hypertension in SSc patients compared with T LCO alone. Here, the objective was to determine whether combined T LCO – T LNO partitioned with recently refined equations could more accurately detect pulmonary hypertension than T LCO alone in SSc. For that purpose, 572 unselected consecutive SSc patients were retrospectively recruited in seven French centres. Pulmonary hypertension was diagnosed with right heart catheterisation in 58 patients. T LCO , T LNO and V C were all lower in SSc patients with pulmonary hypertension than in SSc patients without pulmonary hypertension. The area under the receiver operating characteristic curve for the presence of pulmonary hypertension was equivalent for T LCO (0.82, 95% CI 0.79–0.85) and T LNO (0.80, 95% CI 0.76–0.83), but lower for V C (0.75, 95% CI 0.71–0.78) and D MCO (0.66, 95% CI 0.62–0.70). Compared with T LCO alone, combined T LCO – T LNO does not add capability to detect pulmonary hypertension in unselected SSc patients.