Common Lung Diagnostic Tests

Medically Reviewed by Sabrina Felson, MD on September 13, 2022
5 min read

If you have trouble breathing, your doctor may recommend a few tests to figure out what’s causing it.

Some measure how much air you breathe in or out or how much oxygen is going from your lungs to the rest of your body, while others can show if you have an infection or another problem that’s keeping you from breathing well.

Spirometry. This is the simplest and most common lung test. You breathe in and out as hard as you can through a tube, and your doctor measures the volume of air exhaled at specific time points during a forceful and complete exhalation after a maximal inhalation. It can help diagnose conditions that affect how much air your lungs can hold, like chronic obstructive pulmonary disease (COPD). Doctors will test spirometry before and after albuterol, bronchodilator and see if there is an improvement with the medications which is seen in asthma, but not in COPD.

Challenge test. Your doctor will do spirometry first, then ask you to breathe in a spray of a drug called methacholine, which can irritate your airways and make them narrow. Your doctor will do another spirometry to see how the spray affects your breathing. They’ll repeat this with small doses until you start to wheeze or feel short of breath. Your doctor may give you medicine to open your airways again. This test is not routinely done to diagnose asthma.

If your doctor thinks you have a condition called exercise-induced asthma, they may do a similar version of this test called an exercise challenge. Instead of methacholine, your doctor will ask you to use a treadmill or stationary bike and see how that physical activity affects your breathing.

FeNO test. With this, you blow slowly and steadily into a device, and it measures how much nitric oxide is in the air you breathe out. It’s used with people who have certain types of asthma to see if there’s any inflammation in their lungs and how well steroids are working to control inflammation. It is safe, noninvasive, can be done over and over and is used in kids when spirometry is difficult to perform. 

Peak flow measurement. This uses a small plastic device to see how much air you can blow out of your lungs. You take a deep breath and then breathe out as fast and hard as you can. It’s most often used in people with asthma, a condition that narrows the air passages that lead to your lungs. The test compares each result with your best reading. A number above 80% of your best result is good; a number below 50% means you should get help right away. This test can give you advance warning of an asthma attack.

Pulse oximetry, or “pulse ox.” This test uses a device that measures how much oxygen your red blood cells are carrying. The device is usually clipped onto your fingertip, but it can be attached to your nose, foot, ears, or toes. The results are shown as a percentage, with a good result being over 90%. If your numbers are below 90%, your doctor may give you oxygen to help you breathe.

Plethysmography. This gives your doctor a more exact measurement of how much air your lungs can hold. You’ll sit in a booth with a clip holding your nose shut while you breathe through a mouthpiece. This can tell your doctor if your airways have narrowed or how much an ongoing problem like asthma or COPD has hurt your breathing. It can also help your doctor decide what medicines you need or if you might need surgery.

Diffusion capacity test. This measures how well your lungs pass oxygen to your blood. You’ll breathe in and out through a tube for several minutes, and your doctor may take a sample of your blood to help calculate the results. This test can show if your lungs have been damaged or if you have problems with blood flow.

Chest X-ray. This can be used to look for problems like pneumonia, an infection that makes fluid build up in your lungs. It also can help diagnose cancer or a buildup of scar tissue in your lungs known as pulmonary fibrosis.

Computerized tomography (CT) or positron emission tomography (PET) scans. These are more advanced imaging tests that can be used to find problems that an X-ray might not until they’re further along, like cancer. A CT scan is a series of X-rays taken from different angles that are put together to make a more complete picture. A PET scan uses a special dye that lets your doctor see parts of your body more clearly.

Chest ultrasound. This uses high-frequency sound waves to make an image of your lungs. It can help your doctor see if there’s any fluid buildup in or around your lungs.

Pulmonary angiogram. This is a type of CT scan that focuses on the pulmonary arteries -- the blood vessels that connect your heart and lungs. It’s used to spot a potentially life-threatening blood clot in your lungs known as a pulmonary embolism.

Bronchoscopy. Your doctor will slide a small tube with a camera on the end into your airways. The camera lets them look inside those passages for things like mucus, blood, or tumors. You’ll be given medicine to make you sleepy or to numb your air passages before the test, and you may get oxygen during the test. You may have a sore throat afterward. A bronchoscope can also collect small samples of tissue for testing. This is known as a biopsy, and it’s commonly used to look for diseases like cancer.

Mediastinoscopy. This uses a similar tool to look at the space between your right and left lung lobes behind your breastbone. But doctors have to cut a small hole into your chest to put the device in. Because of that, you’ll be given medicine to make you sleep during the procedure. It’s usually done to take out lymph nodes and look for signs of cancer that has spread from your lungs. This can help doctors figure out the best way to treat the disease.

Pleural biopsy: Your lungs are surrounded by a layer of tissue called the pleura, and some health problems can make fluid build up in the space between the pleura and your lungs. If that’s the case, this test might help your doctor figure out what’s causing it. A pleural biopsy usually uses a needle to get a sample of the tissue. The needle goes into your chest between the ribs on your back. Your doctor will give you medicine to numb the skin around that spot before the test.