Understanding When Pulmonary Function Tests Are Needed

What Pulmonary Function Tests Are and Why Doctors Order Them

Pulmonary function tests, often called PFTs or spirometry tests, measure how well your lungs work. These tests check how much air your lungs can hold, how quickly you can breathe air in and out, and how effectively your lungs move oxygen into your bloodstream. Doctors use these measurements to diagnose lung diseases, track how existing conditions are changing, and see how well treatments are working.

The lungs are responsible for one of your body's most important jobs: exchanging oxygen and carbon dioxide. When you breathe in, oxygen enters your lungs and passes into your blood. When you breathe out, carbon dioxide leaves your body. If this process isn't working properly, your entire body can be affected. Pulmonary function tests give doctors specific numbers and measurements that show exactly where problems might exist.

These tests are painless and non-invasive, meaning nothing enters your body and no needles are used. They typically take 30 to 90 minutes total, though the actual testing portion is much shorter. Most tests involve breathing into a machine called a spirometer, which records the measurements. Some tests may require breathing in special gases or exercising on a treadmill while measurements are taken.

According to the American Lung Association, pulmonary function tests are among the most commonly ordered respiratory tests in medical practice. They're considered the gold standard for measuring lung function because they provide objective, quantifiable data rather than relying on symptoms alone. Symptoms like shortness of breath can have many causes, but PFTs help narrow down whether a lung problem is actually present and how serious it might be.

Practical takeaway: Pulmonary function tests are standard breathing measurements that help doctors see exactly how well your lungs are working. Understanding what these tests measure can help you prepare for them and understand your results.

Common Reasons Doctors Order Pulmonary Function Tests

Doctors order pulmonary function tests for many different reasons. One of the most common reasons is to investigate persistent shortness of breath. If you've been experiencing difficulty breathing for weeks or months, your doctor may want to determine whether this is caused by a lung problem, a heart problem, or something else entirely. PFTs can help rule out or confirm lung-related causes.

People with a history of smoking or those exposed to occupational hazards often receive PFTs as part of screening. Occupational exposures include asbestos, silica dust, coal dust, and various chemical fumes. Workers in industries like mining, construction, manufacturing, and agriculture may need regular lung function testing to catch problems early. The Centers for Disease Control and Prevention reports that occupational lung diseases affect hundreds of thousands of American workers.

Patients with known lung conditions typically need PFTs regularly to monitor their health. Common chronic conditions that require monitoring include:

• Asthma—to measure how well the lungs respond to medications and to track control over time
• Chronic obstructive pulmonary disease (COPD)—to stage the severity and monitor disease progression
• Pulmonary fibrosis—to see if scarring in the lungs is getting worse
• Cystic fibrosis—to assess lung damage and guide treatment decisions
• Emphysema—to measure how much permanent airway damage has occurred

Before certain surgeries, especially major procedures like heart surgery or lung surgery, doctors often order PFTs to understand a patient's baseline lung function. This information helps surgeons and anesthesiologists plan the procedure safely and predict recovery. People about to receive chemotherapy or radiation therapy may also need baseline PFTs, since some cancer treatments can damage lung tissue.

Allergic reactions, infections, and environmental exposures can also prompt testing. For example, a severe respiratory infection that doesn't fully resolve might warrant PFTs to check for lasting damage. Exposure to mold, bird droppings, or other substances can cause conditions like hypersensitivity pneumonitis, which PFTs can help diagnose.

Practical takeaway: PFTs are ordered for many reasons—from investigating new symptoms to monitoring known conditions to preparing for medical procedures. Knowing why your doctor wants the test can help you understand what information they're looking for.

Understanding the Different Types of Pulmonary Function Tests

Several different types of pulmonary function tests exist, and your doctor will order the specific ones that match your situation. The most basic and common test is spirometry. During spirometry, you breathe normally into a mouthpiece connected to a spirometer machine. The machine measures your forced vital capacity (FVC)—the total amount of air you can exhale after taking the deepest breath possible. It also measures your forced expiratory volume in one second (FEV1)—how much of that air you can exhale in just one second. The ratio between FEV1 and FVC helps doctors identify whether you have obstructive lung disease (like asthma or COPD) or restrictive lung disease (like pulmonary fibrosis).

Lung volume measurements go beyond simple spirometry. These tests measure the total amount of air your lungs can hold, including air that remains in your lungs even after you exhale completely. This residual volume is important information that spirometry alone cannot provide. Lung volume is typically measured using a technique called helium dilution or nitrogen washout, where you breathe a mixture of special gases, and the machine calculates how much space is in your lungs based on how diluted those gases become.

Diffusion tests measure how well oxygen passes from your lungs into your blood. During diffusion testing (also called DLCO testing), you inhale a small amount of carbon monoxide mixed with other gases, hold your breath briefly, and then exhale. The machine measures how much carbon monoxide was absorbed. Since carbon monoxide crosses from lungs to blood through the same pathway as oxygen, this test provides information about oxygen transfer. Low diffusion scores can indicate problems like pulmonary fibrosis, emphysema, or pulmonary hypertension.

Bronchial challenge tests measure how sensitive your airways are to certain substances. During these tests, you inhale gradually increasing amounts of methacholine or histamine while spirometry measurements are taken. If your airways are reactive (as in asthma), they will narrow at lower doses, causing your spirometry numbers to drop. These tests help confirm asthma diagnosis and assess asthma severity.

Exercise testing or cardiopulmonary exercise testing (CPET) combines pulmonary function measurement with heart rate and blood oxygen monitoring while you exercise on a treadmill or stationary bike. This test is useful when doctors need to understand how your lungs and heart work together during physical activity, or when they're trying to determine whether shortness of breath comes from lung problems, heart problems, or deconditioning.

Practical takeaway: Different types of PFTs measure different aspects of lung function. Your doctor chooses which tests to order based on your symptoms and medical history. Knowing what each test measures helps you understand what information your doctor is seeking.

Preparing for Pulmonary Function Testing

Proper preparation helps ensure accurate test results. Several days before your test, avoid respiratory irritants and substances that might affect your airways. This means staying away from strong perfumes, smoke, paint fumes, and other chemical odors. If you have asthma and use a rescue inhaler, try to minimize your need for it in the days leading up to testing. Your doctor may specifically instruct you to avoid using certain medications before the test.

On the day of testing, wear loose, comfortable clothing that doesn't restrict your chest or abdomen. Tight clothing can interfere with your ability to breathe deeply. Avoid eating a large meal right before testing, as a full stomach can make deep breathing uncomfortable. It's fine to eat something light a few hours before your appointment.

Bring a list of all medications you're currently taking, including inhalers, and discuss them with the technician. Some medications can affect test results. For example, bronchodilators (medications that open airways) can improve your test numbers, so your doctor needs to know whether you've recently used these medications. If you wear dentures, you may be asked to remove them so the mouthpiece fits properly and the seal is tight enough for accurate measurements.

Arrive early to complete paperwork and allow time