Clinical significance of elevated diffusing capacity.
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.


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.


METHODS
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.


CONCLUSIONS
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.
Saydain
Ghulam
G
Pulmonary and Critical Care Division, Nassau University Medical Center, 2201 Hempstead Turnpike, East Meadow, NY 11554, USA. gsaydain@numc.edu
Beck
Kenneth C
KC
Decker
Paul A
PA
Cowl
Clayton T
CT
Scanlon
Paul D
PD
D000328:Adult; D000368:Aged; D000402:Airway Obstruction / Q000175:diagnosis* / Q000209:etiology; D001249:Asthma / Q000150:complications* / Q000175:diagnosis; D001784:Blood Gas Analysis; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications* / Q000175:diagnosis; D011237:Predictive Value of Tests; D011336:Probability; D011379:Prognosis; D011446:Prospective Studies; D011653:Pulmonary Diffusing Capacity; D012016:Reference Values; D012129:Respiratory Function Tests; D012680:Sensitivity and Specificity; D014109:Total Lung Capacity