Table 3– The TL,NO/TL,CO ratio in different situations and conditions
TL,NO/TL,COSituation/diagnosisExplanation
IncreasedHigh PO2 anaemia (uncorrected) [11]Less binding sites available for CO which lowers TL,CO but not TL,NO
IncreasedHeavy smokers [27]
Diffuse parenchymal disease# [24]
Chronic thromboembolic pulmonary hypertension [24]
Hepatopulmonary syndrome [25]
Pulmonary artery occlusion in sheep [34]
Greater involvement of microvascular compartment reduces TL,CO more than TL,NO
DecreasedRest to exercise (normals) [22]
Voluntary restriction of lung expansion [13] mimicking “extrapulmonary restriction”
Expansion of capillary volume (per unit VA) increases TL,CO more than TL,NO
DecreasedSarcoidosis [29]
Lifelong altitude exposure+ [23]
Cystic fibrosis [26]
Morbid obesity [19]
Chronic heart failure [35] (unconfirmed for TL,NO/TL,CO ratio)
Alveolar surface area reduction exceeds microvascular damage, and affects TL,NO more than TL,CO
  • TL,NO: transfer factor of the lung for nitric oxide; TL,CO: transfer factor of the lung for carbon monoxide; PO2: oxygen tension; CO: carbon monoxide; VA: alveolar volume. #: weighted towards sarcoidosis with end-stage disease; : sarcoidosis in stages II–III and younger than those in #; +: “highlanders”, corrected for polycythaemia.