Lung Function Tests

Sarcoidosis is a disease in which tiny clumps of inflammatory cells known as granulomas form in different tissues in the body. The lungs, lymph nodes, skin, and eyes are the organs most commonly affected. 

When sarcoidosis affects the lungs, it leads to symptoms such as chest pain, wheezing, shortness of breath, and a chronic, dry cough.

Lung function tests, or pulmonary function tests, are used to monitor the progression of sarcoidosis and may also be used to diagnose the condition. These tests assess how well the patient’s lungs are working.

Such tests are also the best way to monitor the severity of sarcoidosis, so patients are often tested repeatedly over time. This allows doctors to determine whether the patient needs treatment, or whether a given treatment in use is sufficient.

A variety of tests measure different aspects of lung function. These tests are listed and described below.


Spirometry is a test that estimates the size of the lungs and measures the rate of air flow in and out of the lungs. During the test, the patient breathes into a tube connected to a computer. The patient will be asked both to exhale normally, and as hard as possible.

Lung volume tests

Lung volume tests measure how much air the patient’s lungs can hold. There are two common types of lung volume tests: whole body plethysmography, and helium or nitrogen dilution test.

In plethysmography, the patient is asked to sit in a clear cubicle, similar to a phone booth, and breathe in and out of a mouthpiece. Changes in pressure inside the cubicle are used to determine lung volume.

In the helium or nitrogen dilution test, the patient is asked to breathe in and out of a tube connected to a chamber and measurement device. A small amount of a harmless gas (either helium or nitrogen) is added to the air. Changes in the concentration of that gas in the chamber are used to determine lung volume.

Lung diffusion capacity test

The lung diffusion capacity test estimates how well the oxygen that the patient breathes in enters the bloodstream. During the test, the patient is asked to breathe normally in and out of a tube for a several minutes. In some cases, a small amount of blood may also be drawn to measure hemoglobin levels.

Another technique for estimating how well oxygen makes its way from the lungs into the blood stream is the diffusing capacity of carbon monoxide test, or DLCO. During this test, the patient is asked to breathe in and out of a mouthpiece and a tiny, harmless amount of carbon monoxide is added to the air the patient is inhaling. The test actually directly measures how well carbon monoxide diffuses into the bloodstream, and this value is used to estimate how well oxygen would also diffuse.

Pulse oximetry

Pulse oximetry is used to estimate oxygen levels in the blood. During this painless test, a pulse oximeter probe (similar to a clothes pin) is placed on the fingertip and on another body surface, such as the earlobe.

Arterial blood gas tests

Arterial blood gas tests measure the amounts of oxygen and carbon dioxide in the patient’s blood. These gases make their way in and out of the bloodstream via the lungs. For this test, blood is typically drawn from an artery, such as those in the wrist or arm, and analyzed in a laboratory.

Fractional exhaled nitric oxide tests

Fractional exhaled nitric oxide tests measure how much nitric oxide is present in the air the patient exhales. The amount of nitric oxide is an indicator of the amount of swelling in the airways. During the test, the patient is asked to breathe normally in and out of a tube.


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