Clinical Significance of Elevated Diffusing Capacity

Ghulam Saydain, Kenneth C. Beck, Paul A. Decker, Clayton T. Cowl, Paul D. Scanlon

Research output: Contribution to journalArticlepeer-review

64 Scopus citations


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/m2, 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.

Original languageEnglish (US)
Pages (from-to)446-452
Number of pages7
Issue number2
StatePublished - Feb 2004


  • Asthma
  • Diffusing capacity
  • Obesity
  • Pulmonary function test

ASJC Scopus subject areas

  • Pulmonary and Respiratory Medicine
  • Critical Care and Intensive Care Medicine
  • Cardiology and Cardiovascular Medicine


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