Diagnosing Chronic Obstructive Lung Disease

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Highlights	Complications	Oxygen-Replacement Therapy
Introduction	Risk Factors	Lifestyle Changes
Causes	Diagnostic Tests	Surgical Procedures
Symptoms	Treatment	Resources
Diseases with Similar Symptoms	Medications	References

The patient is asked to breathe in and breathe out forcefully into an instrument. This is repeated several times. The force of the air is then measured. From the results, the physician determines two important values:

The forced vital capacity (FVC). FVC is the maximum volume of air that a patient can breathe out with force. It indicates lung size, elasticity, and how well the air passages open and close.

The forced expiratory volume in one second (FEV1). FEV1 is the maximum volume of air that a patient can breathe out in 1 second after breathing in fully. Airflow is considered to be limited if the forced breath out stays low over 1 second. People with COPD have a decline in FEV1 over time. FEV1 is measured as "percent of predicted:"

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Moderate COPD is an FEV1 50 - 80% of predicted.
Severe COPD is an FEV1 30 - 50% of predicted.
The ratio of FEV1 to FVC (FEV1/FVC) is less than 70% of normal, regardless of whether the patient has an FEV1 greater than 80% or less than 50%.

Spirometry is a painless study of air volume and flow rate in the lungs. Spirometry is frequently used to evaluate lung function in people with diseases such as asthma or cystic fibrosis.

Tests for Measuring the Ability of the Lung to Exchange Oxygen and Carbon Dioxide

Arterial Blood Gas. The physician may request an arterial blood gas test to determine the amount of oxygen and carbon dioxide in the blood (its saturation). Low oxygen (hypoxia) and high carbon dioxide (hypercapnia) levels often indicate chronic bronchitis, but not always emphysema. A blood gas analysis that shows very low oxygen levels is useful for determining which patients would benefit from oxygen therapy (see below). This procedure typically involves drawing blood from an artery in the wrist.

Click the icon to see a depiction of arterial blood gas sampling.

Pulse Oximetry Test. A safe and painless test for measuring oxygen in the blood is called pulse oximetry, which involves placing a probe on the finger or ear lobe. The probe emits two different lights. The amount of each light the blood absorbs is related to how much oxygen the red blood cells carry. This test measures only oxygen in the blood, however, and not carbon dioxide. Results should be taken together with other tests to determine the need for medication or oxygen therapy.