The Diffusing Capacity of the Lung for Carbon Monoxide (DLCO) measures how effectively gases transfer from the lungs into the bloodstream. It is a key component of lung function tests, assessing the efficiency of gas exchange within the respiratory system. This measurement helps healthcare providers understand an individual’s lung health and function.
The DLCO Test Explained
The DLCO test is a non-invasive and quick procedure used to evaluate lung function. During the test, a person breathes through a mouthpiece with nose clips, ensuring all air passes through the equipment. They exhale completely, then rapidly inhale a gas mixture containing a small, harmless amount of carbon monoxide, along with a tracer gas like helium or methane.
After inhaling, the individual holds their breath for about 10 seconds. This brief breath-hold allows for carbon monoxide absorption into the bloodstream. The person then exhales fully into the machine, which measures the amount of carbon monoxide absorbed and exhaled. The difference indicates how efficiently the gas transferred from the lungs into the blood. This process is typically repeated at least once to ensure accurate results.
Understanding Normal DLCO Values
A “normal” DLCO value is a predicted range tailored to each individual, not a single universal number. These predicted values are established through extensive population studies, considering various demographic characteristics. Factors such as age, sex, height, and sometimes race influence what is considered a typical DLCO for a given person.
Actual DLCO test results are commonly expressed as a percentage of this predicted value. A normal DLCO result typically falls between 75% and 140% of the predicted value. This percentage range signifies that the lungs are effectively transferring gases, indicating healthy diffusion capacity for someone with similar characteristics.
Variables Affecting DLCO Results
Several physiological and environmental factors can influence DLCO measurements. Age is a significant factor, as DLCO naturally decreases over time due to aging. Biological sex also plays a role, with males typically exhibiting higher DLCO values than females. Height is another consideration, as greater height generally correlates with larger lung volumes and, consequently, higher DLCO.
Hemoglobin levels in the blood also impact DLCO results. For instance, anemia can lower DLCO because there is less hemoglobin available to bind carbon monoxide, while polycythemia (an elevated red blood cell count) can increase it. Altitude affects results, with DLCO tending to be lower at higher elevations due to changes in oxygen levels. Smoking status is also relevant, as smoking can reduce DLCO by damaging the alveolar-capillary membrane. These variables are routinely accounted for when calculating an individual’s predicted normal range.
What Abnormal DLCO Values Mean
DLCO values falling outside the normal range suggest alterations in the lungs’ ability to exchange gases. A lower-than-normal DLCO typically indicates impaired gas transfer, meaning the lungs are not efficiently moving oxygen into the blood. This impairment can stem from issues affecting the alveolar-capillary membrane, which is the thin barrier where gas exchange occurs, or from reduced blood flow to the lungs.
Conditions that damage the alveoli, such as emphysema, can reduce the surface area available for gas exchange, leading to low DLCO. Diseases that cause thickening or scarring of the alveolar-capillary membrane, like pulmonary fibrosis or sarcoidosis, also impair diffusion. Additionally, conditions affecting blood flow to the lungs, such as pulmonary hypertension or pulmonary embolism, can result in a decreased DLCO.
Conversely, a higher-than-normal DLCO is less common but can occur in specific situations. This might suggest an increased volume of blood in the lungs’ capillaries, as seen in conditions like pulmonary hemorrhage where blood in the alveoli binds the carbon monoxide. Other factors that can lead to an elevated DLCO include obesity, asthma, and polycythemia. DLCO results are one piece of a comprehensive assessment. Healthcare professionals interpret these values alongside other lung function tests, a person’s symptoms, and their complete medical history.