Doctors check your lungs using a combination of methods that range from simply listening to your chest with a stethoscope to advanced imaging and breathing tests. The approach depends on your symptoms, medical history, and what your doctor suspects might be going on. Most lung evaluations start with a hands-on physical exam and expand from there if needed.
The Physical Exam
The first thing most doctors do is listen to your lungs with a stethoscope, a technique called auscultation. They’ll ask you to breathe deeply through your mouth while they place the stethoscope on several spots across your chest and back. Normal breathing produces a soft, rustling sound. What they’re really listening for are abnormal sounds layered on top of that.
Wheezes are high-pitched, musical sounds that usually happen when you breathe out. They signal narrowed airways and are common in asthma and COPD. Crackles sound like velcro being pulled apart or like rice cereal popping. They can point to fluid in the lungs, pneumonia, or scarring. Stridor is a harsh, high-pitched sound during inhalation that suggests the upper airway is partially blocked. A pleural rub sounds like two pieces of leather rubbing together and can indicate inflammation of the lining around the lungs.
Beyond listening, your doctor may tap on your chest and back with their fingers. This is called percussion. Healthy, air-filled lungs produce a hollow, resonant sound when tapped. If the sound turns dull or flat, it can mean fluid has collected in the space around the lungs. Your doctor might ask you to breathe deeply while they continue tapping, checking whether the sound changes with your breathing. If it doesn’t shift at all, that’s another clue that fluid may be present.
Pulse Oximetry
That small clip placed on your fingertip during a doctor’s visit is a pulse oximeter. It shines light through your skin to estimate how much oxygen your red blood cells are carrying. For most people, a normal reading falls between 95% and 100%. A reading of 92% or lower is a concern worth calling your doctor about. At 88% or below, it’s an emergency.
Pulse oximetry is quick, painless, and gives an immediate snapshot of how well your lungs are delivering oxygen to your blood. Its limitation is that it only measures oxygen saturation. It can’t tell your doctor about carbon dioxide levels, blood acidity, or whether you’ve been exposed to carbon monoxide, all of which require a blood draw.
Arterial Blood Gas Testing
When a pulse oximeter isn’t detailed enough, doctors may order an arterial blood gas test. This involves drawing blood from an artery, usually in your wrist, rather than a vein. It’s more uncomfortable than a standard blood draw, but it provides a much fuller picture: your blood’s oxygen level, carbon dioxide level, and acidity (pH). These values reveal how effectively your lungs are exchanging gases and whether your body’s chemistry is in balance. Elevated carbon dioxide, for example, can indicate that your lungs aren’t clearing waste gases efficiently, something a finger clip would never catch.
Spirometry and Breathing Tests
Spirometry is the most common pulmonary function test. You breathe into a mouthpiece connected to a machine while wearing a nose clip. After taking the deepest breath you can, you blow out as hard and fast as possible until your lungs are completely empty. The machine measures two key numbers: your forced vital capacity (the total volume of air you can blow out) and your forced expiratory volume in one second (how much air comes out in that first second of blowing). Comparing these two values helps your doctor determine whether your airways are obstructed, whether your lungs can’t fully expand, or both.
A separate test called lung diffusion testing goes a step further. You breathe in a gas containing a tiny, harmless amount of carbon monoxide, hold your breath briefly, then exhale into the machine. The machine measures how much carbon monoxide your blood absorbed. If less than expected made it from your air sacs into your bloodstream, it suggests the membrane between your lungs and blood vessels isn’t transferring oxygen efficiently. This can point to conditions like pulmonary fibrosis or emphysema.
Preparing for Breathing Tests
If you have a spirometry or other pulmonary function test scheduled, there are a few things to keep in mind. Don’t eat a large meal within two hours of the test. Avoid heavy exercise for at least 30 minutes beforehand. Skip alcohol for at least four hours before, and don’t smoke on the day of the test. Wear loose clothing that lets you take a full, deep breath. If you use an inhaler, your doctor will likely tell you to stop using it for a specific window before the test, ranging from 6 hours for short-acting inhalers to 36 hours for longer-acting ones. This ensures the test captures your baseline lung function rather than the effect of medication.
Chest X-Rays and CT Scans
A chest X-ray is often the first imaging test doctors order. It’s fast, widely available, and gives a broad view of the lungs, heart, and surrounding structures. It can reveal pneumonia, large masses, fluid buildup, and collapsed lung tissue. But X-rays have limits. They produce a flat, two-dimensional image, and smaller or more subtle abnormalities can hide behind bones or blend into surrounding tissue.
A CT scan takes dozens of cross-sectional images and assembles them into a detailed, three-dimensional picture. It’s significantly better at detecting small lung nodules, early-stage tumors, blood clots in the pulmonary arteries, and subtle pneumothorax (a small pocket of air leaking outside the lung). In trauma patients, CT scans catch lung bruising, tiny rib fractures, and bleeding near the spine or chest that X-rays routinely miss.
For lung cancer screening specifically, the U.S. Preventive Services Task Force recommends a yearly low-dose CT scan for people between 50 and 80 years old who have a 20 pack-year or greater smoking history and either still smoke or quit within the past 15 years. A pack-year equals smoking about one pack per day for one year, so someone who smoked two packs a day for 10 years has a 20 pack-year history.
Bronchoscopy
When imaging and breathing tests aren’t enough to make a diagnosis, doctors may look directly inside your airways using a bronchoscopy. A thin, flexible tube with a camera on the end is guided through your nose or mouth, down your throat, and into your lungs. You’re typically sedated and your throat is numbed with a local anesthetic. The procedure itself takes about 30 to 60 minutes, but with preparation and recovery time, expect to be at the facility for around four hours.
During the procedure, doctors can visually inspect your airways for tumors, inflammation, or bleeding. They can also collect tissue samples or wash small amounts of fluid into a section of the lung and suction it back out for lab analysis. Afterward, you’ll be monitored for several hours. You won’t be able to eat or drink until the numbness in your throat wears off completely and you can swallow and cough normally again. Most people go home the same day.
How These Tests Work Together
Doctors rarely rely on a single test. A physical exam might reveal crackles in your lower lungs, prompting a chest X-ray that shows a hazy area suggesting fluid or infection. If the X-ray is inconclusive, a CT scan provides more detail. If your doctor suspects your breathing capacity is declining over time, spirometry tracks that trend across visits. Pulse oximetry offers a quick check at every appointment, while arterial blood gas testing fills in the gaps during acute illness or before surgery.
The specific combination depends entirely on what your doctor is trying to answer. A routine checkup for a healthy person might involve nothing more than a stethoscope and a quick pulse oximetry reading. A persistent cough that hasn’t responded to treatment could eventually lead through imaging, breathing tests, and a bronchoscopy before a clear answer emerges.