A pulmonologist uses a range of tests to figure out how well your lungs work, why you’re having symptoms, and what’s causing them. The specific tests depend on your symptoms, but most people start with breathing tests and imaging before moving to more specialized procedures. Here’s what to expect.
Pulmonary Function Tests
Pulmonary function tests (PFTs) are the bread and butter of a pulmonology workup. They measure how much air your lungs can hold, how quickly you can move air in and out, and how efficiently oxygen reaches your bloodstream. You’ll likely encounter one or more of these during your first or second visit.
Spirometry
Spirometry is the most common breathing test and often the first one ordered. You breathe into a mouthpiece connected to a recording device while wearing a nose clip so all air flows through your mouth. After inhaling as deeply as you can, you exhale as hard and fast as possible. The machine records the volume of air you move and how long each breath takes. This test picks up conditions like asthma, COPD, and restrictive lung diseases by revealing whether airflow is blocked or lung capacity is reduced.
Lung Volume Measurement
Spirometry gives estimates of lung volume, but when your pulmonologist needs precise numbers, they’ll use one of two methods. Body plethysmography puts you inside a sealed, clear plastic booth. As you breathe, the booth measures changes in air pressure and calculates your total lung capacity from those shifts. The other option, gas dilution, has you inhale a known amount of a harmless gas (usually helium) and then measures how much you exhale. A computer works backward from that number to determine your lung volume.
Diffusion Capacity
This test checks how well oxygen passes from your air sacs into your bloodstream. You inhale a tiny amount of carbon monoxide, hold your breath for about 10 seconds, then exhale into a detector. Carbon monoxide behaves similarly to oxygen in the lungs, so if your lungs don’t absorb it well, they aren’t exchanging oxygen efficiently either. Low diffusion capacity can point to conditions like pulmonary fibrosis, emphysema, or problems with the blood vessels in your lungs.
Exhaled Nitric Oxide (FeNO) Testing
If asthma or airway inflammation is suspected, your pulmonologist may measure the level of nitric oxide in your breath. You breathe slowly and steadily into a handheld device, and it gives a reading in parts per billion (ppb) within seconds. In adults, a reading below 25 ppb suggests that a specific type of inflammation responsive to inhaled steroids is unlikely. A reading above 50 ppb strongly suggests that inflammation is present and steroids will probably help. Readings between 25 and 50 ppb fall in a gray zone that your doctor will interpret alongside your symptoms and other results.
Bronchial Challenge Testing
When spirometry results look normal but asthma is still suspected, a methacholine challenge test can provoke the airways to reveal hidden sensitivity. You inhale gradually increasing concentrations of methacholine, a substance that narrows the airways in people with asthma. After each dose, spirometry is repeated. The test is considered positive if your lung function drops by 20% or more. How little methacholine it takes to trigger that drop indicates the degree of airway sensitivity: a response at 8 mg/mL or less is classified as hyperresponsive, while a response between 8 and 16 mg/mL is considered borderline.
Chest Imaging
A standard chest X-ray is typically the starting point for imaging, but it has limits. When X-rays look normal despite ongoing symptoms, or when your pulmonologist needs finer detail, they’ll order a high-resolution CT scan (HRCT). This specialized scan produces detailed cross-sectional images that can reveal changes in your smallest airways, air sacs, and the tissue surrounding them. It’s particularly useful for diagnosing interstitial lung disease (including pulmonary fibrosis and sarcoidosis), emphysema, small airway disease, and certain rare conditions. Think of it as the difference between looking at a map from space versus street level.
Arterial Blood Gas Analysis
An arterial blood gas (ABG) test measures oxygen and carbon dioxide levels directly from a blood sample taken from an artery, usually in your wrist. It’s more accurate than a finger pulse oximeter. The test also measures blood acidity and bicarbonate levels, which together reveal whether your lungs are keeping up with the body’s demand for gas exchange. Normal arterial oxygen runs between 80 and 110 mmHg, and normal carbon dioxide sits between 34 and 45 mmHg. Values outside those ranges help your pulmonologist determine whether you’re retaining carbon dioxide (a sign of ventilation problems) or not absorbing enough oxygen.
Exercise and Walking Tests
Some lung problems only show up during physical activity. The six-minute walk test (6MWT) is one of the simplest and most widely used functional assessments. You walk at your own pace along a flat corridor for six minutes while your oxygen levels are monitored with a finger clip. The distance you cover and any drop in oxygen saturation are both recorded. In healthy people, oxygen levels dip only slightly during the test (less than 1% on average), so a significant drop signals that your lungs or heart can’t keep up with the increased demand. The 6MWT also correlates strongly with disease severity in COPD, pulmonary fibrosis, and heart failure, making it useful for tracking how a condition progresses over time.
Sleep Studies
If you snore heavily, wake up gasping, or feel exhausted despite a full night’s sleep, your pulmonologist may order a polysomnography (sleep study). This can be done in a sleep lab or sometimes at home with a portable monitor. The test records your breathing, oxygen levels, heart rate, brain waves, and body movements throughout the night.
The key number is the Apnea-Hypopnea Index (AHI), which counts how many times per hour your breathing stops or becomes significantly shallow. An AHI below 5 is normal. Between 5 and 15 is mild sleep apnea, 15 to 30 is moderate, and 30 or above is severe. Oxygen dips are also graded: drops that stay above 90% are considered mild, dips into the 80s are moderate, and anything below 80% is severe. Home sleep studies report a similar number called the Respiratory Event Index (REI), calculated slightly differently but used the same way.
Bronchoscopy
Bronchoscopy is a more invasive procedure reserved for situations where other tests haven’t provided a clear answer, or when your pulmonologist needs tissue samples. A thin, flexible tube with a camera is guided through your nose or mouth and down into your airways. You’re typically sedated for this, so you won’t feel much.
Once inside, the pulmonologist can visually inspect your airways and collect samples in several ways: washing a section of the lung with saline and collecting the fluid, brushing cells from the airway walls, or using small tools to take tissue biopsies. Ultrasound guidance through the bronchoscope helps target specific areas, especially for suspicious masses or lymph nodes. Bronchoscopy can also be therapeutic, used to remove foreign objects, control bleeding, or reduce the size of an airway tumor with a laser.
Lung Biopsies
When a mass, nodule, or unexplained lung abnormality needs a definitive diagnosis, a biopsy provides tissue for analysis. Pulmonologists use two main approaches, each with different tradeoffs.
Transbronchial biopsy is done during a bronchoscopy, reaching the target through the airways. It’s less invasive and carries lower complication risks: severe bleeding occurs in fewer than 0.1% of cases, and the chance of a collapsed lung requiring a chest tube is about 0.5%. The tradeoff is lower diagnostic accuracy, with a sensitivity around 69% for peripheral lung cancers.
CT-guided needle biopsy involves inserting a needle through the chest wall while a CT scanner guides placement. It’s significantly more accurate, with a sensitivity of about 94%, but carries somewhat higher risks: a 1.1% rate of collapsed lung needing a chest tube and a 0.3% rate of significant bleeding. Your pulmonologist will choose the approach based on where the abnormality sits in your lungs, its size, and your overall health.
Respiratory Muscle Strength Testing
If weakness in the muscles you use to breathe is suspected, particularly in people with neuromuscular diseases, your pulmonologist can measure how much pressure you generate when you inhale and exhale forcefully against a sealed gauge. Low readings point to muscle weakness as a contributor to breathing problems, which requires a different treatment approach than conditions affecting the lungs themselves. This test is quick, noninvasive, and helps distinguish between lungs that can’t exchange air properly and muscles that can’t move air effectively.