A pulmonologist uses a range of tests to measure how well your lungs work, identify the cause of breathing problems, and monitor chronic conditions like asthma or COPD. These tests range from simple breathing exercises that take a few minutes to overnight sleep studies and camera-guided procedures inside your airways. The specific tests you’ll encounter depend on your symptoms, but most visits start with some form of pulmonary function testing.
Spirometry: The Most Common Breathing Test
Spirometry is the foundation of pulmonary testing and often the first thing a pulmonologist orders. You breathe into a mouthpiece connected to a machine, inhale as deeply as you can, then blow out as hard and fast as possible. The test measures three key things: how much air you can force out in one second (FEV1), the total volume of air you can exhale in a full breath (FVC), and the ratio between the two.
A normal FEV1/FVC ratio is above 0.70, and both FEV1 and FVC should be at or above 80% of the predicted value for someone your age, height, and sex. When the ratio drops below 0.70, it signals an obstructive problem, meaning air has trouble getting out of your lungs. This is the hallmark pattern in asthma and COPD. The FEV1 percentage then grades severity: above 70% of predicted is mild, 60 to 69% is moderate, 50 to 59% is moderately severe, 35 to 49% is severe, and below 35% is very severe.
A different pattern, where the ratio stays normal but total volumes are low, points to a restrictive problem. This means your lungs can’t fully expand, which happens in conditions like pulmonary fibrosis or chest wall disorders. Spirometry alone can suggest restriction, but confirming it usually requires a more advanced test.
Body Plethysmography for Full Lung Volumes
Standard spirometry only captures the air you can move in and out. It can’t measure the air that stays trapped in your lungs after you exhale completely (residual volume) or your total lung capacity. Body plethysmography fills that gap. You sit inside a sealed, transparent booth about the size of a phone booth and breathe through a mouthpiece while pressure sensors track tiny changes in the air around you.
This test is particularly valuable for people with COPD, where air trapping is a major issue. In these patients, plethysmography typically measures total lung capacity 2 to 3 liters higher than other methods because it captures all the gas in the lungs, including pockets in poorly ventilated areas. That accuracy makes it essential for distinguishing between obstructive and restrictive diseases and for tracking how a condition changes over time.
Exhaled Nitric Oxide (FeNO) Testing
This quick, noninvasive test helps diagnose and manage asthma by measuring inflammation in your airways. Healthy lungs produce a small amount of nitric oxide. When a specific type of inflammation is present, the kind driven by the immune cells involved in allergic asthma, nitric oxide production rises. You breathe out slowly and steadily into a device that measures the gas in parts per billion.
In children, a reading of 35 ppb or higher strongly suggests asthma and predicts a good response to inhaled steroid therapy. FeNO is especially useful before starting steroid treatment, since a high reading beforehand helps confirm the diagnosis and gives your pulmonologist a baseline to measure treatment effectiveness. It can also help explain why a persistent cough isn’t responding to standard treatment: if FeNO is low, the problem likely isn’t the type of inflammation that steroids address.
The Six-Minute Walk Test
Not every test involves machines and mouthpieces. The six-minute walk test is exactly what it sounds like: you walk along a flat corridor at your own pace for six minutes while a technician tracks the distance you cover and monitors your oxygen levels and heart rate. It’s a low-intensity exercise test designed to reflect how your lungs perform during everyday activity rather than at peak exertion.
The test is performed on a straight, flat hallway at least 30 meters long, with markers every 3 meters. You set your own speed, and if you need to stop and rest, the clock keeps running. If you already use supplemental oxygen, you use it during the test. The technician gives standardized encouragement at one-minute intervals but won’t coach your pace. Your oxygen saturation is monitored continuously, and the test is stopped if it drops below 80%.
Pulmonologists use this test to assess functional capacity in chronic lung diseases, gauge disease progression, evaluate whether supplemental oxygen is needed, and measure how well treatments are working.
Arterial Blood Gas Analysis
While a pulse oximeter clipped to your finger estimates oxygen levels, an arterial blood gas test gives a complete picture of how well your lungs exchange gases. A small blood sample is drawn from an artery, usually at the wrist, and analyzed for oxygen levels, carbon dioxide levels, blood acidity, and bicarbonate.
Normal ranges are: pH between 7.35 and 7.45, oxygen (PaO2) between 75 and 100 mm Hg, carbon dioxide (PaCO2) between 35 and 45 mm Hg, and oxygen saturation between 95 and 100%. A high carbon dioxide level suggests your lungs aren’t clearing waste gas effectively, which is common in advanced COPD. A low oxygen level with normal carbon dioxide might point to a problem with gas exchange at the tissue level. Together, these numbers help your pulmonologist understand not just whether you’re getting enough oxygen, but why you might not be.
Sleep Studies
Pulmonologists frequently diagnose and manage sleep apnea, a condition where breathing repeatedly stops during sleep. A polysomnography, or overnight sleep study, is the standard diagnostic test. You spend a night in a sleep lab (or sometimes use a home testing device) while sensors track your breathing patterns, oxygen levels, brain waves, heart rate, and body movements.
The key measurement is the apnea-hypopnea index (AHI), which counts how many times per hour your breathing stops or significantly decreases. An AHI below 5 is normal. Between 5 and 14 is mild sleep apnea, 15 to 30 is moderate, and above 30 is severe. The risk of related health problems like high blood pressure rises substantially around an AHI of 30. That said, the AHI is one piece of the puzzle. Pulmonologists also weigh your symptoms, oxygen dips during sleep, and overall health when deciding on treatment.
Bronchoscopy
When imaging or breathing tests raise concerns that need a closer look, a pulmonologist may perform a bronchoscopy. A thin, flexible tube with a camera is guided through your nose or mouth and down into your airways. The procedure allows direct visualization of the bronchial tubes and can serve both diagnostic and therapeutic purposes.
Diagnostically, a bronchoscopy can identify the cause of a persistent cough, unexplained bleeding, or an abnormal spot seen on imaging. During the procedure, your pulmonologist can take tissue samples (biopsies), collect fluid by washing a section of the airway with saline and retrieving it for lab analysis, or culture mucus to check for infections. Therapeutically, it can remove blockages, treat tumors, control bleeding, or place a stent to hold open a narrowed airway.
Endobronchial Ultrasound (EBUS)
A specialized form of bronchoscopy combines the camera with an ultrasound probe at the tip of the scope. This allows the pulmonologist to see lymph nodes and structures just outside the airway walls, then guide a needle into them in real time to collect tissue samples. Its most important role is in staging lung cancer: determining whether cancer has spread to lymph nodes in the chest, which directly affects treatment decisions. EBUS is minimally invasive compared to the surgical alternative (mediastinoscopy), avoids general anesthesia, and can also diagnose non-cancerous conditions like sarcoidosis and tuberculosis.
Chest Imaging
While radiologists typically read the images, pulmonologists order and interpret chest X-rays and CT scans as part of their diagnostic workup. A standard chest X-ray is a quick first look at the lungs, useful for spotting pneumonia, fluid buildup, or large masses. But it has limits: CT scans are significantly better at detecting smaller abnormalities like early-stage nodules, subtle pneumothoraces, and lung contusions.
High-resolution CT scans are essential for diagnosing interstitial lung diseases like pulmonary fibrosis, where the damage occurs in fine tissue structures that a plain X-ray can’t resolve. Pulmonologists also use low-dose CT for lung cancer screening in high-risk patients.
How to Prepare for Pulmonary Testing
Preparation matters, especially for breathing tests where medications can skew results. If you’re scheduled for spirometry with bronchodilator testing, you’ll need to stop certain inhalers ahead of time. Short-acting rescue inhalers like albuterol should be withheld for at least 6 hours. Short-acting anticholinergic inhalers need a 12-hour window. Long-acting inhalers require 24 to 36 hours, and ultra-long-acting agents need 36 to 48 hours. Your pulmonologist’s office should give you specific instructions for your medications.
Beyond inhalers, general preparation guidelines include: no smoking on the day of the test, no alcohol for at least 4 hours, no heavy meals within 2 to 3 hours, no heavy exercise for 30 minutes beforehand, and avoid caffeine for 12 hours. Wear comfortable, loose-fitting clothes that don’t restrict a deep breath. Arriving late by more than 30 minutes may mean rescheduling, since the lab schedules testing windows carefully.