Can Pulmonary Function Tests (PFTs) assess Diffusing Capacity of the Lung for Carbon Monoxide (DLCO)?

From the Guidelines

Yes, Pulmonary Function Tests (PFTs) can assess the Diffusing Capacity of the Lung for Carbon Monoxide (DLCO). DLCO is a specific component of comprehensive PFTs that measures how effectively gases transfer from the lungs into the bloodstream 1. During this test, a patient inhales a small amount of carbon monoxide, holds their breath for about 10 seconds, and then exhales. The difference between the amount of carbon monoxide inhaled and exhaled indicates how well oxygen can diffuse across the alveolar-capillary membrane.

Key Points to Consider

• This measurement is particularly valuable for evaluating conditions like pulmonary fibrosis, emphysema, pulmonary hypertension, and sarcoidosis that affect gas exchange.
• DLCO results are typically reported in ml/min/mmHg and are compared to predicted values based on the patient's age, height, sex, and sometimes ethnicity.
• Reduced DLCO values suggest impaired gas transfer, which may occur due to decreased surface area for gas exchange, thickening of the alveolar-capillary membrane, or reduced pulmonary capillary blood volume.
• Interpreting the DL,CO, in conjunction with spirometry and lung volumes assessment, may assist in diagnosing the underlying disease 1.
• Adjustments of DL,CO for changes in haemoglobin and carboxyhaemoglobin are important, especially in situations where patients are being monitored for possible drug toxicity, and where haemoglobin is subject to large shifts 1.

Clinical Application

The test is safe, non-invasive, and provides crucial information about lung function that spirometry alone cannot assess. For instance, normal spirometry and lung volumes associated with decreased DL,CO may suggest anaemia, pulmonary vascular disorders, early ILD or early emphysema 1.

Severity of Decrease in DLCO

The severity of decrease in DLCO can be graded as follows:

• Mild: 60% and >LLN
• Moderate: 40–60%
• Severe: <40 Where % pred is the percent predicted and LLN is the lower limit of normal 1.

From the Research

Assessment of DLCO using PFTs

• Pulmonary Function Tests (PFTs) can assess the Diffusing Capacity of the Lung for Carbon Monoxide (DLCO) 2, 3, 4, 5, 6.
• DLCO is measured as part of PFTs to assess gas transfer in the lungs, and its implications are well-recognized in various clinical conditions 2, 3, 6.
• A low DLCO is associated with increased morbidity and mortality, while a high DLCO is often seen in patients with obesity and asthma 2, 3.

Clinical Significance of DLCO

• DLCO is an important predictor of postoperative morbidity in patients undergoing pulmonary resection 4.
• A low DLCO is associated with increased respiratory morbidity, and the percent predicted DLCO provides an objective index of disease severity and prognosis 2, 4, 6.
• DLCO can help differentiate between various clinical conditions, such as emphysema, chronic asthma, and interstitial lung disease 2.

Measurement of DLCO

• DLCO can be measured using a portable device, and the test requires minimal effort from the patient 2.
• The measurement of DLCO is an important part of PFTs, and it can be used to assess the severity of various lung diseases 2, 4, 6.
• DLCO can be adjusted for hemoglobin and alveolar volume to provide a more accurate assessment of lung function 4.