The T_L,NO /T_L,CO ratio cannot be used to exclude pulmonary embolism

The existing screening modalities for pulmonary embolism (PE), such as D-dimer and clinical prediction rules, have low positive predictive values. With its capability to indicate pulmonary vascular abnormalities, the ratio of the transfer factor of the lungs for nitric oxide and the transfer factor of the lungs for carbon monoxide (T_L,NO /T_L,CO ) might be an additional discriminating parameter.

Carbon monoxide/Nitric oxide diffusion measurements were performed on unselected patients seen on the emergency department for which due to suspected PE a computed tomography pulmonary angiogram (CTPA) was ordered.

A total of 28 patients were included, PE was found in 12 on CTPA. Median T_L,NO /T_L,CO ratio was 4·09 (interquartile range (IQR) 3·83-4·40) in the no PE group versus 4·00 (IQR 3·78-4·32) in the PE group (P = 0·959). Median alveolar volume was 77·1% of predicted in the no PE group versus 71·0% of predicted in the PE group (P = 0·353). Median T_L,CO was 75·8% of predicted in the no PE group versus 68·8% of predicted in the PE group (P = 0·120). Median T_L,NO was 69·3% of predicted in the no PE group versus 60·5% of predicted in the PE group (P = 0·078).

The presented data indicate that the T_L,NO /T_L,CO ratio cannot be used to exclude PE.