From the Guidelines
A normal DLCO value is typically considered to be above 80% of the predicted value, based on a person's age, height, sex, and sometimes ethnicity, as indicated by recent guidelines 1.
Definition of Normal DLCO
The normal diffusing capacity of the lungs for carbon monoxide (DLCO) is a measure of how effectively oxygen moves from the air sacs in the lungs into the bloodstream.
- The DLCO test uses carbon monoxide as a surrogate gas to assess the lung's ability to transfer gases.
- This measurement reflects the functional surface area available for gas exchange in the lungs.
- DLCO values can be affected by various factors including hemoglobin levels, lung volume, and cardiac output, which is why results are often adjusted for these variables.
Interpretation of DLCO Values
- A reduced DLCO may indicate conditions that affect the lung parenchyma, pulmonary vasculature, or alveolar-capillary membrane.
- Elevated DLCO values are less common but can occur in conditions like polycythemia or pulmonary hemorrhage.
- The severity of reductions in DLCO can be graded, with mild reductions being above 60% of the predicted value, moderate reductions between 40-60%, and severe reductions below 40% 1.
- Interpreting DLCO in conjunction with spirometry and lung volumes assessment can help diagnose the underlying disease.
Clinical Significance of DLCO
- A low DLCO is seen in patients with interstitial lung disease, sarcoidosis, pulmonary fibrosis, chronic pulmonary embolism, and primary pulmonary hypertension.
- A high DLCO is associated with asthma, obesity, and intrapulmonary hemorrhage.
- Adjustments of DLCO for changes in hemoglobin and carboxyhemoglobin are important, especially in situations where patients are being monitored for possible drug toxicity.
- The most recent and highest quality study on this topic is from 1, which provides the most up-to-date guidance on the interpretation of DLCO values.
From the Research
Normal DLCO Values
The normal values for Diffusing Capacity of the Lung for Carbon Monoxide (DLCO) can vary depending on several factors such as age, sex, height, and hemoglobin level.
- A study published in the journal Respiration 2 mentions that the general study population showed improvements in DLCO, but it does not provide a specific normal range for DLCO.
- However, it is generally accepted that a normal DLCO value is typically above 80% of the predicted value, but the exact normal range can vary depending on the laboratory and the specific testing equipment used.
Factors Affecting DLCO
Several factors can affect DLCO values, including:
- Lung disease, such as chronic obstructive pulmonary disease (COPD) 3, 4, 5, 6
- Anemia or other conditions that affect hemoglobin level
- Age and sex
- Height and body size
- Smoking history
Measurement of DLCO
DLCO is typically measured using a pulmonary function test called the diffusing capacity test.
- This test involves breathing in a small amount of carbon monoxide and then holding their breath for a short period of time 2.
- The amount of carbon monoxide absorbed by the lungs is then measured, and the DLCO value is calculated based on this measurement.