COPD (Chronic Obstructive Pulmonary Disease) is a generic term used to cover two conditions – chronic bronchitis and emphysema. Both cause obstruction of the airways, though in different ways, and reduce oxygen-CO2 exchange efficiency. As a result, detailed tests are required to distinguish the two diseases. But a set of generic tests which measure airflow, blood oxygen levels, and other factors are still used in an initial diagnosis of COPD.

Spirometry Tests

The first COPD test is a non-invasive test called lung spirometry. Spirometry evaluates lung capacity by measuring the lung’s ability to exchange air. The spirometry test requires the patient to deeply inhale and then exhale air into a measurement tube. Three components are then measured: FEV1 (forced expiratory volume after one second), FEF25-75 (forced expiratory flow at 25% to 75%) and FVC (forced vital capacity). These measurements are ranked by your doctor and compared to healthy patients. An initial COPD diagnosis is made if the patient ranks lower than 70% compared to a healthy person.

The spirometry test is typically performed several times. In some cases, a bronchodilator is used which lessens the airway restriction and then a “post-bronchodilator spirometry” test is performed. Using this method, your physician can both confirm the COPD diagnosis and tell if the condition can be treated effectively.

Lung Volume

Doctors also measure lung volume using gas dilution or plethysmography. Lung dilution involves inhaling nitrogen or helium and measuring the gas volume to determine lung volume. Body plethysmography requires the patient getting into an airtight chamber and breathing in and out through a tube. The air volume is measured as pressure changes in the chamber to determine the approximate lung volume of the patient. These tests results are going to be adjusted based on a patient’s height, age, and other factors so that the patient can be compared to similar people with healthy lungs.

Diffusion Capacity Test

Since the primary function of the alveoli (the tiny sacs at the end of the bronchioles or airways) is to enable gas exchange (of O2 and CO2), a measure of their diffusion capacity is diagnostic. In this test, the patient inhales a small amount of CO (carbon monoxide). In large amounts it is toxic, but at the levels of the test it is perfectly safe. The amount taken up into the blood is measured by extracting a blood sample and measuring the CO content. This is one way in which emphysema is detected.

Oximetry Testing

Similarly, the amount of dissolved oxygen in the blood provides useful information for diagnosing COPD. There are several ways to go about it. One test takes a sample of arterial blood and measures the oxygen content. But the test is somewhat painful since extracting blood from an artery is more uncomfortable than from a vein (the usual method). So, an alternative called oximetry is sometimes used. In this method, a device shines a light through the finger or thumb and the amount transmitted is measured on the other side. Since the amount of light is related to how much oxygen is in the blood, the device can make a non-chemical measurement without requiring a sample. The downside is that the test is less accurate than measuring arterial blood gases (ABG).

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