Abstract
DLCOreports and interpretation should be standardised and include adjusting predictedDLCOandKCOfor lung volumehttp://ow.ly/ywTA30cOh44
To the Editor:
The American Thoracic Society (ATS) and European Respiratory Society (ERS) should be congratulated on updating standards for diffusing capacity of the lung for carbon monoxide (DLCO) [1]. I agree that “Besides varying with age, sex, height and possible ethnicity,DLCOalso changes with Hb, lung volume, COHb,PIO2…, exercise and body position.” and that “adjustments for these factors be made in the predicted rather than the measuredDLCO”. Reporting transfer coefficient of the lung for carbon monoxide (KCO) rather thanDLCO/alveolar volume (VA) will help get away from the mistaken notion thatDLCO/VA“corrects”DLCOfor lung volume [2]. While the new standards describe how to adjust predictedDLCOfor haemoglobin (Hb), COHb and inspired oxygen tension (PIO2), it does not discuss how to adjust predictedDLCOandKCOfor lung volume.
The following equations [3] were included in the 2005 ATS/ERSDLCOstandards [4], and describe how to adjustDLCOandKCOfor lung volume. They were developed studying normal subjects with experimental reductions in inspired volume (VI; and thusVA) and fit the model thatDLCOandKCO改变的方式来回m havingDLCOreduced proportionate to the surface area for gas exchange with the capillary blood component unchanged. Mathematically, they result inDLCO% predicted for lung volume equalingKCO% predicted for lung volume when using the equationKCO(predicted)=DLCO(predicted)/VA(predicted).
DLCO[predicted for lung volume]=DLCO[predicted]×(0.58+0.42×(VAm/VAp))
KCO[predicted for lung volume]=KCO[predicted]×(0.42+0.58/(VAm/VAp))
withVAm/VAp=measuredVA/predictedVA.
For example, atVA50% of predicted, theDLCOpredicted for lung volume is 80% andKCOis 160% of that forVA100% of predicted.
The standards require reportingDLCOandKCO(adjusted, predicted) with specification of the adjustments. Additional reporting requirements should includeDLCO(% of adjusted predicted) andVA(% predicted).
Neither the 2005 nor the current standards address how to reportDLCOandKCOadjusted for lung volume, or how to interpretDLCO.
In addition to knowing % predictedDLCOandKCOadjusted for all factors except lung volume, it is also very helpful to know % predictedDLCOandKCOwhen also adjusted for lung volume [2]. Just as adjusting predictedDLCOandKCOfor haemoglobin in an anaemic patient yields a better indication of the lung's ability of gas exchange, adjustingDLCOandKCOfor lung volume in a patient with low lung volume yields a better indication of the lung's ability of gas exchange.
A shorter nomenclature is needed forDLCOandKCO% predicted also adjusted for lung volume.
I proposeDACOandKACOto refer toDLCOandKCOpredicted values that have been adjusted for lung volume (the “A” refers to adjusted for lung volume.)
Reporting requirements should includeDACO(adjusted, predicted),KACO(adjusted, predicted), as well asDACO(% of adjusted predicted) andKACO(% of adjusted predicted).
The new standards recommend development of a standardised common report form. I propose the following, one when Hb is not measured (box 1) and a second when Hb is measured (box 2), with both including % of FVC forVIif spirometry was done the same day
Diffusing capacity | Predicted range | Actual | % pred | ||
Mean | 95% | ||||
DLCOmL·min−1·mmHg−1 | xx.xx | xx.xx | dd.dd | xx | Predicted not adjusted for Hb |
VA(BTPS) L | x.x x | x.x x | x.x x | xx | |
KCOmL·min−1·mmHg−1·L−1 | xx.xx | xx.xx | x.x x | xx | Predicted not adjusted for Hb |
VI(BTPS) L | x.x x | x.x x | xx.xx | xx | xx% of FVC |
DACOmL·min−1·mmHg−1 | xx.xx | xx.xx | dd.dd | yy | Predicted adjusted for lung volume |
DLCOandKCOare yy% predicted, adjusted for lung volume.
Common report form for diffusing capacity when haemoglobin measurements are not taken
Diffusing capacity | Predicted range | Actual | % pred | Hb xx.x from D-MON-YYYY | |
Mean | 95% | ||||
DLCOmL·min−1·mmHg−1 | xx.xx | xx.xx | dd.dd | xx | Predicted not adjusted for Hb |
DLCOmL·min−1·mmHg−1 | xx.xx | xx.xx | dd.dd | xx | Predicted adjusted for Hb |
VA(BTPS) L | x.x x | x.x x | x.x x | xx | |
KCOmL·min−1·mmHg−1·L−1 | xx.xx | xx.xx | x.x x | xx | Predicted adjusted for Hb |
VI(BTPS) L | x.x x | x.x x | x.x x | xx | xx% of FVC |
DACOmL·min−1·mmHg−1 | xx.xx | xx.xx | dd.dd | yy | Predicted adjusted for lung volume and Hb |
DLCOandKCOare yy% predicted, adjusted for lung volume and Hb.
Common report form for diffusing capacity when haemoglobin measurements are taken
For both reports, ifDLCOandKCOpredicted were also adjusted for COHb and/or PIO2, then a line saying “PredictedDLCOandKCO还调整了……”应该出现在最后,which includes the data used to make the adjustment, such as “COHb of 2.6% and altitude of 2000m.” The 95% values are the lower limit of normal (LLN), withDACO[LLN]=DACO[adjusted,predicted]×DLCO[LLN]/DLCO[predicted].
There is not a clear consensus on interpretation ofDLCO. I recommend the following algorithm to interpretDLCO, withDLCO% predicted, adjusted and LLN the lower limit of normal (box 3).
DLCO≥80% and ≥LLN | DLCOis normal |
DLCO<80% but ≥LLN | DLCOis near lower limit of normal |
DLCO≥60%, <80%, and |
DLCOis mildly reduced |
DLCO≥40%, <60%, and |
DLCOis moderately reduced |
DLCO<40% | DLCOis severely reduced |
Interpretation of diffusing capacity values
IfDLCOis not normal, andDLCOadjusted for lung volume (DACO) is above the LLN as % predicted, then add phrase “due to low lung volume”.
IfDLCOis not normal, andDLCOadjusted for lung volume is below the LLN as % predicted but more than 10% predicted greater thanDLCO, then add phrase “in part due to low lung volume”.
As a co-author of the 2005 ERS/ATSDLCOstandards, I believe including adjustments ofDLCOfor lung volume and standardised reports and interpretation would improve the clinical value ofDLCO.
Footnotes
Conflict of interest: None declared.
- ReceivedMay 8, 2017.
- AcceptedMay 31, 2017.
- Copyright ©ERS 2017