Carbon monoxide transfer coefficient

Last revised by Yuranga Weerakkody on 28 Feb 2024

Citation, DOI, disclosures and article data

Citation:

Weerakkody Y, Rock P, Di Muzio B, Carbon monoxide transfer coefficient. Reference article, Radiopaedia.org (Accessed on 24 Apr 2024) https://doi.org/10.53347/rID-80732

DOI:

https://doi.org/10.53347/rID-80732

Permalink:

https://radiopaedia.org/articles/80732

rID:

80732

Article created:

1 Aug 2020, Yuranga Weerakkody ◉

Disclosures:

At the time the article was created Yuranga Weerakkody had no recorded disclosures.

View Yuranga Weerakkody's current disclosures

Last revised:

28 Feb 2024, Yuranga Weerakkody ◉

Disclosures:

At the time the article was last revised Yuranga Weerakkody had no financial relationships to ineligible companies to disclose.

View Yuranga Weerakkody's current disclosures

Revisions:

4 times, by 3 contributors - see full revision history and disclosures

Systems:

Chest

Synonyms:

Carbon monoxide transfer coefficient (KCO)
KCO

Carbon monoxide transfer coefficient (often abbreviated as KCO) is a parameter often performed as part of pulmonary function tests. It is also often written as DLCO/VA (diffusing capacity per liter of lung volume) and is an index of the efficiency of alveolar transfer of carbon monoxide.

Interpretation of KCO depends on other parameters such as

VA: accessible alveolar volume
TLC: total lung capacity

Interpretation

In the context of normal VA, a low KCO (provided there is no anemia or recent smoking) could suggest³:

pulmonary vascular disease
- pulmonary hypertension
- pulmonary vasculitis
- intrapulmonary right-to-left shunting
- early emphysema

In the context of a low VA, the next step is to look at the VA/TLC ratio.

Low VA/TLC ratio (< 0.8)
- a normal KCO (not able to be interpreted): this could imply obstruction with ventilation distribution abnormalities, the KCO might turn “normal”. In this scenario, no further valid inferences can be made regarding KCO
- however, if KCO is low despite those caveats this could imply extensive impairment in pulmonary gas exchange efficiency, e.g. severe emphysema
Normal VA/TLC ratio (≥ 0.8)
- a high KCO indicates a predominance of VC over VA due to
  - incomplete alveolar expansion but preserved gas exchange i.e. extra-parenchymal restriction such as pleural, chest wall or neuromuscular disease)
  - an increase in pulmonary blood flow from areas of diffuse (pneumonectomy) or localized (local destructive lesions/atelectasis) loss of gas exchange units to areas with preserved parenchyma; this frequently leads to more modest increases in KCO (although a high KCO can also be seen with normal VA when there is "increased pulmonary blood flow" or redistribution (e.g. left-to-right shunt and asthma)
  - extra-vascular hemoglobin (e.g. alveolar hemorrhage)
- a low KCO: could suggest intra-parenchymal restriction with impaired gas exchange efficiency as in some interstitial lung diseases (ILD)
- a normal KCO: could suggest intra-parenchymal restriction with preserved KCO (can be a common finding in patients with HRCT abnormalities showing a pattern consistent with idiopathic interstitial pneumonia); normal KCO, therefore, should not be misinterpreted as “no ILD”