Diffusing Capacity (DLCO)

Diffusing capacity, or DLCO (diffusing capacity of the lung for carbon monoxide), is a breathing test that measures how well oxygen can pass from the air sacs in your lungs into your bloodstream. You inhale a tiny, safe amount of carbon monoxide, hold your breath for about 10 seconds, then exhale; the machine calculates how much gas your lungs absorbed. It is one of the most sensitive tests for detecting the kind of lung damage asbestos causes.

Origin

The technique was developed by Marie and August Krogh in the early 1900s and refined into the modern single-breath method by Robert Forster and colleagues at the University of Pennsylvania in the 1950s. The acronym stands for "Diffusing capacity of the Lung for Carbon mOnoxide." In Europe and parts of the Commonwealth, the same test is reported as TLCO (Transfer factor).

Significance in Asbestos Context

DLCO is often the first pulmonary function value to drop in asbestosis, because the scarring caused by asbestos thickens the wall between the air sacs and the tiny blood vessels that absorb oxygen. Your DLCO can fall while your overall lung volume (FVC) and airflow (FEV1) still look normal, which is why pulmonologists order it whenever asbestos exposure is suspected.

For a claim or lawsuit, DLCO matters in two specific ways. First, it is one of the three values (along with FVC and FEV1) that the AMA Guides to the Evaluation of Permanent Impairment use to assign a percentage of pulmonary impairment, which directly affects the value of asbestos trust payouts and workers' compensation awards. A DLCO under roughly 60% of predicted generally falls into the moderate-to-severe impairment range. Second, serial DLCO results over months or years can document progression, powerful evidence that the disease is real, ongoing, and consistent with asbestos rather than a fixed problem from another cause.

Defense medical experts routinely argue that a low DLCO is caused by smoking, emphysema, obesity, anemia, heart failure, or pulmonary hypertension rather than asbestos. The clinical answer is pattern recognition: asbestosis classically produces a restrictive pattern (reduced lung volumes) with a reduced DLCO and a preserved or even elevated FEV1/FVC ratio, which looks different from the obstructive pattern of smoking-related COPD. Testing must follow American Thoracic Society/European Respiratory Society standards and be corrected for hemoglobin, or the result can be challenged or excluded.

Example Sentence

Her pulmonologist noted that the DLCO had dropped from 78% of predicted three years ago to 52% today, which, together with the CT findings of bilateral interstitial fibrosis and a 30-year shipyard work history, confirmed progressive asbestosis.

Related Terms

Pulmonary Function Test (PFT), Asbestosis, Spirometry, FVC, FEV1, Restrictive Lung Disease, AMA Impairment Rating, Interstitial Lung Disease, Pleural Thickening

Notes

• Ask that your DLCO be performed at an ATS/ERS-accredited pulmonary function lab and that the report include a hemoglobin-corrected value; uncorrected results from an anemic patient can be unfairly low and are a common target of defense challenges.
• Request DLCO testing even if your spirometry (FVC, FEV1) is normal. An isolated drop in DLCO may be the earliest measurable sign of asbestos-related lung scarring.
• Keep every PFT report you have ever had, including older ones from employer physicals or unrelated hospitalizations; a documented decline in DLCO over time is among the strongest evidence of progressive asbestos disease.
• A normal DLCO does not rule out asbestos-related disease. Pleural plaques, diffuse pleural thickening, and especially early mesothelioma can be present with preserved gas exchange, so do not let a normal result delay imaging or specialist referral.
• Before filing a trust or workers' compensation claim, confirm with your attorney that your records include DLCO, FVC, FEV1, and total lung capacity (TLC). All are typically needed for an AMA impairment rating.