Clinical significance of elevated diffusing capacity

Chest. 2004 Feb;125(2):446-52. doi: 10.1378/chest.125.2.446.


Study objective: Single-breath diffusing capacity of the lung for carbon monoxide (DLCO) is used as a pulmonary function test (PFT) to assess gas transfer in the lungs. The implications of a low DLCO are well-recognized, but the clinical significance of a high DLCO is not clear. The aim of this study was to identify the clinical correlates of a high DLCO.

Patients and methods: We identified 245 patients with a high DLCO (ie, > 140% predicted) and a matched group of 245 patients with normal DLCO (ie, 85 to 115% predicted), who were selected from a laboratory database of 45,000 patients tested between January 1997 and December 1999. We compared the demographic features, clinical diagnoses, and PFT data between the two groups.

Settings: Large multispecialty group practice.

Results: The patients in the high DLCO group were heavier (mean [+/- SD] weight, 96.0 +/- 22.9 vs 85.0 +/- 21.3 kg, respectively; p < 0.001), had a higher mean body mass index (32.9 +/- 7.4 vs 29.4 +/- 6.4 kg/m(2), respectively; p < 0.001), larger body surface area (p < 0.001), and larger mean total lung capacity (p = 0.007) and alveolar volume (p < 0.001). The clinical diagnoses of obesity (p < 0.001) and asthma (p < 0.001) were more common among patients with high DLCO values. The majority of patients (62%) with a high DLCO had a diagnosis of obesity, asthma, or both. Polycythemia, hemoptysis, and left-to-right shunt were uncommon.

Conclusion: A high DLCO on a PFT is most frequently associated with large lung volumes, obesity, and asthma. Other conditions are much less common. A clinical condition, which typically reduces DLCO, may deceptively normalize DLCO in such patients.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adult
  • Aged
  • Airway Obstruction / diagnosis*
  • Airway Obstruction / etiology
  • Asthma / complications*
  • Asthma / diagnosis
  • Blood Gas Analysis
  • Case-Control Studies
  • Female
  • Humans
  • Male
  • Middle Aged
  • Obesity / complications*
  • Obesity / diagnosis
  • Predictive Value of Tests
  • Probability
  • Prognosis
  • Prospective Studies
  • Pulmonary Diffusing Capacity*
  • Reference Values
  • Respiratory Function Tests
  • Sensitivity and Specificity
  • Total Lung Capacity