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Correspondence |

Impact of Hemoglobin and Carboxyhemoglobin Adjustment on the Interpretation of Pulmonary Diffusing Capacity in a General Population FREE TO VIEW

Jeffrey M. Haynes, RRT, RPFT; Gregg L. Ruppel, MEd, RRT, RPFT; David A. Kaminsky, MD, FCCP
Author and Funding Information

OTHER CONTRIBUTIONS: The authors thank William C. Stephan, MD, FCCP, for assistance with this study.

FINANCIAL/NONFINANCIAL DISCLOSURES: The authors have reported to CHEST the following: J. M. H. is a consultant for Morgan Scientific, Inc; G. L. R. is a consultant for ndd Medical Technologies, Inc and BioMarin Pharmaceutical, Inc and a paid speaker for MGC Diagnostics Corporation; D. A. K. is a paid speaker for MGC Diagnostics Corporation.

aPulmonary Function Laboratory, St. Joseph Hospital, Nashua, NH

bDivision of Pulmonary, Critical Care, and Sleep Medicine, St. Louis University School of Medicine, St. Louis, MO

cDivision of Pulmonary and Critical Care Medicine, University of Vermont College of Medicine, Burlington, VT

CORRESPONDENCE TO: Jeffrey M. Haynes, RRT, RPFT, Pulmonary Function Laboratory, St. Joseph Hospital, 172 Kinsley St, Nashua, NH 03060


Copyright 2017, American College of Chest Physicians. All Rights Reserved.


Chest. 2017;151(5):1188-1189. doi:10.1016/j.chest.2016.12.019
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Diffusing capacity of the lung for carbon monoxide (Dlco) is an important test for diagnosis, monitoring of disease progression, and response to therapy. The 2005 American Thoracic Society/European Respiratory Society Standardization of Lung Function Testing Task Force recommended that Dlco adjustments for hemoglobin and carboxyhemoglobin (COHb) “should always be made to ensure appropriate interpretation.” We conducted a study to examine the impact of Dlco adjustment on the interpretation of individual Dlco test results in a general population.

Our study was a retrospective review of Dlco test data collected over a 12-month period in a pulmonary function laboratory (St. Joseph Hospital, Nashua, NH). This study was approved by the St. Joseph Hospital Institutional Review Board (SJH IRB File 2016-01). The primary outcome was the frequency of an adjusted Dlco value migrating above or below the lower limit of normal (LLN) according to Cotes et al. For test data in which the unadjusted and adjusted values were both < LLN, the frequency of a test result changing severity classification was examined. The frequency of an adjusted Dlco changing by > 3 mL/min/mm Hg was also determined.

Data from 372 Dlco tests were included in the analysis. Only 20 of 372 tests (5.4%) resulted in a change in normality classification (≥ LLN vs < LLN) after hemoglobin and COHb adjustment. Of these tests, only two were associated with a Dlco value change > 3 mL/min/mm Hg, both having a low hemoglobin value. Five test results changed from normal to < LLN and 15 changed from < LLN to normal (Fig 1). Two hundred and twenty-eight test results had values < LLN before and after hemoglobin and COHb adjustment. Of these tests, 23 of 228 (10.1%) had a change in severity score after adjustment (see Table 1). Of these tests, only one was associated with a Dlco value change > 3 mL/min/mm Hg. In total, only five (1.3%) Dlco tests changed by > 3 mL/min/mm Hg, and all were associated with low hemoglobin values.

Figure Jump LinkFigure 1 Impact of hemoglobin and carboxyhemoglobin (≥ 2%) adjustment on Dlco test normality classification. Δ = change; Dlco = diffusing capacity of the lung for carbon monoxide; LLN = lower limit of normal.Grahic Jump Location

Table Graphic Jump Location
Table 1 Dlco Tests Resulting in Changed Severity Classification (Less Than Lower Limit of Normal)

COHb = carboxyhemoglobin; Dlco = diffusing capacity of the lung for carbon monoxide; LLN = lower limit of normal.

In a general population, Dlco adjustment infrequently affected individual test interpretation. In almost all cases, the change in Dlco after adjustment did not exceed the recommended within-test variability of ≤ 3 mL/min/mm Hg. However, we recognize that in some patients Dlco adjustment may be very important, particularly if a reduced Dlco can be attributed to anemia. We cannot comment on the impact of Dlco adjustment on the interpretation of longitudinal data. We encourage more research in various patient populations to identify subjects in whom Dlco adjustment may have a significant impact on test interpretation.

References

Macintyre N. .Crapo R.O. .Viegi G. .et al Standardisation of the single-breath determination of carbon monoxide uptake in the lung. Eur Respir J. 2005;26:720-735 [PubMed]journal. [CrossRef] [PubMed]
 
Cotes J.E. .Chinn D.J. .Quanjer P.H. .Roca J. .Yernault J.C. . Standardization of the measurement of transfer factor (diffusing capacity): report working party standardization of lung function tests, European Community for Steel and Coal: official statement of the European Respiratory Society. Eur Respir J Suppl. 1993;16:41-52 [PubMed]journal. [PubMed]
 
Pellegrino R. .Viegi G. .Brusasco V. .et al Interpretative strategies for lung function tests. Eur Respir J. 2005;26:948-968 [PubMed]journal. [CrossRef] [PubMed]
 

Figures

Figure Jump LinkFigure 1 Impact of hemoglobin and carboxyhemoglobin (≥ 2%) adjustment on Dlco test normality classification. Δ = change; Dlco = diffusing capacity of the lung for carbon monoxide; LLN = lower limit of normal.Grahic Jump Location

Tables

Table Graphic Jump Location
Table 1 Dlco Tests Resulting in Changed Severity Classification (Less Than Lower Limit of Normal)

COHb = carboxyhemoglobin; Dlco = diffusing capacity of the lung for carbon monoxide; LLN = lower limit of normal.

References

Macintyre N. .Crapo R.O. .Viegi G. .et al Standardisation of the single-breath determination of carbon monoxide uptake in the lung. Eur Respir J. 2005;26:720-735 [PubMed]journal. [CrossRef] [PubMed]
 
Cotes J.E. .Chinn D.J. .Quanjer P.H. .Roca J. .Yernault J.C. . Standardization of the measurement of transfer factor (diffusing capacity): report working party standardization of lung function tests, European Community for Steel and Coal: official statement of the European Respiratory Society. Eur Respir J Suppl. 1993;16:41-52 [PubMed]journal. [PubMed]
 
Pellegrino R. .Viegi G. .Brusasco V. .et al Interpretative strategies for lung function tests. Eur Respir J. 2005;26:948-968 [PubMed]journal. [CrossRef] [PubMed]
 
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