When Is a Pulmonary Function Test Required? 7 Clinical Triggers Explained

Introduction: What It Feels Like to Be Told You Need a Pulmonary Function Test

For many people, hearing a doctor say “I’d like to order a pulmonary function test” triggers a wave of quiet worry. What did they find? Is something wrong with my lungs? That reaction is completely understandable, and it is worth stating clearly: being asked to take this test is not a diagnosis, and it is not a reason to panic.

A pulmonary function test (PFT) is a noninvasive breathing test. There are no needles, no radiation, and no surgery involved. Instead, a PFT measures how well the lungs move air in and out and how efficiently they exchange oxygen and carbon dioxide. Because it is so gentle, it is suitable for both children and adults. The most common temporary side effects, such as mild lightheadedness or a bit of coughing, resolve on their own within minutes.

PFTs are among the most frequently ordered tests in pulmonary medicine, and for good reason. More than 35 million Americans live with chronic lung disease such as asthma and COPD. This article walks through the seven most common clinical triggers that lead a physician to order a PFT, explains the main types of tests, and describes what to expect, so patients can feel informed rather than anxious.

What Is a Pulmonary Function Test, Really?

A PFT is not a single test but a group of noninvasive breathing assessments that measure lung volume, capacity, airflow rates, and gas exchange. Together, these measurements paint a detailed picture of how the lungs are performing.

Importantly, a PFT does not provide a standalone diagnosis. Results must be interpreted alongside a patient’s clinical history, physical exam, and other laboratory data. Think of it as one important piece of a larger puzzle that a physician assembles.

The Three Main Types of PFTs

• Spirometry: The most common PFT. It measures the amount of air a person inhales and exhales, along with the force of exhalation. Spirometry offers a broad overview of lung function and is the standard starting point for most evaluations.
• Diffusion Capacity (DLCO): This test measures how efficiently oxygen passes from the lungs into the bloodstream. It is especially useful for detecting conditions like pulmonary fibrosis and has become a key metric in Long COVID evaluations.
• Body Plethysmography: Performed inside an airtight booth, this test measures total lung volume and air trapped in the lungs. It is used when more detailed volume measurements are needed, such as in COPD or restrictive lung disease workups.

A physician determines which test, or combination of tests, is appropriate based on the clinical question being asked. Specialized centers also offer additional assessments such as methacholine challenge, FeNO testing, and exercise challenge testing, which extend the diagnostic picture for conditions like asthma.

7 Clinical Triggers That Require a Pulmonary Function Test

The following seven scenarios are the ones most likely to prompt a physician to order a PFT. Some are symptom-driven, some are condition-driven, some are preventive or occupational, and one reflects an emerging area of medicine. Together, they represent the full clinical spectrum.

Trigger 1: Persistent or Unexplained Respiratory Symptoms

Certain symptoms are the body’s way of signaling that lung function deserves an objective look. These include a persistent cough lasting more than three weeks, shortness of breath during routine activities, wheezing or noisy breathing, chest tightness during physical activity, and decreased exercise tolerance. Recurring respiratory infections such as bronchitis or pneumonia may also prompt a PFT to check whether underlying airway disease is contributing.

None of these symptoms, on their own, confirm a lung condition. A PFT simply helps clarify the picture and guide appropriate treatment.

Trigger 2: Diagnosing or Ruling Out a Known Lung Condition

PFTs are essential for diagnosing and staging major lung diseases including asthma, COPD, pulmonary fibrosis, cystic fibrosis, and interstitial lung disease. Spirometry helps distinguish between two broad patterns: obstructive conditions, where airflow is blocked (as in asthma and COPD), and restrictive conditions, where lung volume is reduced (as in pulmonary fibrosis).

The scale of these diseases is significant. In 2023, the age-adjusted prevalence of diagnosed COPD in U.S. adults was 3.8%, rising to 10.5% in adults age 75 and older (CDC NCHS Data Brief). Asthma affects roughly 29 million Americans. A PFT helps physicians quantify disease severity as mild, moderate, or severe, which directly shapes treatment decisions.

Trigger 3: Monitoring Disease Progression and Treatment Response

PFTs are not only ordered at diagnosis. They are used repeatedly over time to track whether a lung condition is stable, improving, or worsening (ERS/ATS Technical Standard). Serial PFTs help physicians assess whether medications such as bronchodilators or inhaled steroids are working effectively.

This is especially important for asthma and COPD, where lung function can fluctuate and treatment plans require regular adjustment. FeNO testing serves as a complementary tool for monitoring airway inflammation in asthma patients. Being asked to return for repeat PFTs is a sign of thorough, proactive care, not a cause for alarm.

Trigger 4: Pre-Surgical Evaluation

Surgeons and anesthesiologists often require PFTs before thoracic or upper abdominal procedures to assess operative risk and plan perioperative care. Research published in 2024 found that preoperative PFTs in high-risk patients can identify previously unknown respiratory impairments that may influence outcomes (PMC 2024).

This is particularly relevant for patients with a smoking history, obesity, or known cardiopulmonary conditions, even if they feel well going into surgery. A pre-surgical PFT is a protective measure designed to make surgery safer.

Trigger 5: Occupational Exposure and OSHA-Mandated Testing

This is an often-overlooked trigger. Workers in certain industries are legally required to undergo spirometry testing under OSHA standards. Regulated hazards that mandate PFT surveillance include asbestos, cadmium, coke oven emissions, cotton dust, formaldehyde, and benzene.

Workers exposed to silica, coal dust, or chemical irritants, as well as those required to wear respirators, may also need regular testing. These occupational PFTs serve as a baseline and ongoing surveillance tool to detect early lung damage before it becomes symptomatic. While employers may arrange this testing, workers with concerns about their exposures can also seek independent testing. Facilities such as Belmar Cardiopulmonary Diagnostic Center offer occupational spirometry testing for both employers and individual workers.

Trigger 6: Long COVID and Post-Infectious Respiratory Monitoring

Long COVID has emerged as an increasingly recognized indication for PFTs. Research published in 2025 found that Long COVID patients with persistent symptoms such as dyspnea often demonstrate lower DLCO values, suggesting long-term lung injury and ongoing inflammation. A separate 2025 study of healthcare workers emphasized the need for ongoing respiratory monitoring in occupational settings after COVID-19 (PMC 2025).

Even patients who had mild or moderate COVID-19 may experience lingering breathlessness, reduced exercise tolerance, or fatigue that warrants objective assessment. Diffusion capacity (DLCO) testing is among the most sensitive tools for detecting subtle post-COVID lung changes that may not appear on a chest X-ray. Testing after any significant respiratory infection may be warranted if symptoms persist.

Trigger 7: Routine Monitoring, Risk-Factor Screening, and Age-Related Changes

Sometimes a physician orders a PFT even when a patient feels perfectly well. Lung function naturally declines with age, and periodic assessment helps distinguish expected age-related changes from early disease progression.

Populations that may benefit from screening PFTs without active symptoms include long-term smokers or former smokers, individuals with a family history of lung disease, patients on medications with known pulmonary toxicity (such as certain chemotherapy agents or amiodarone), and those with systemic conditions that affect the lungs (such as rheumatoid arthritis or scleroderma). PFTs can also support ADA documentation when respiratory limitations affect a patient’s ability to work. Catching early decline before symptoms appear allows for earlier intervention and better long-term outcomes.

A Note on Race-Neutral Spirometry: What Changed and Why It Matters

Historically, spirometry reference equations were race-specific, an approach critics argued could systematically underestimate lung disease in certain populations. In April 2023, the ATS and ERS released a recommendation advocating for race-neutral spirometry reference equations to reduce racial bias in interpretation.

The practical implication is straightforward: patients who had a PFT before 2023 may have had results interpreted using race-specific equations, which is a worthwhile conversation to have with a physician. In 2025, the ATS published further guidance proposing standardized language for reporting PFT results, improving consistency across clinical settings. Staying current with these evolving standards is part of delivering fair, accurate care.

What Happens After a Pulmonary Function Test?

Once the test is complete, results are reviewed by a board-certified physician and communicated to the ordering provider, who then discusses the findings with the patient. This is where clarity matters most.

An “abnormal” result does not automatically mean serious disease. It means further evaluation or a treatment adjustment may be needed. PFTs quantify both severity (mild, moderate, or severe impairment) and pattern (obstructive, restrictive, or mixed), which helps guide next steps. A PFT result is a starting point for a conversation with a physician, not a verdict. At Belmar Cardiopulmonary Diagnostic Center, results are handled with a compassionate, patient-centered approach that defines every aspect of care at the center.

Conclusion: Knowledge Reduces Anxiety, and PFTs Are Here to Help

Across these seven triggers, including persistent symptoms, diagnosing lung conditions, monitoring treatment, pre-surgical evaluation, occupational testing, Long COVID monitoring, and routine screening, one theme holds true: being told a PFT is needed is not cause for alarm. It is a physician’s way of gathering objective, accurate information about lung health.

PFTs are safe, noninvasive, and designed with patient well-being in mind. Understanding why a test is ordered, and what to expect from it, is one of the most effective ways to reduce anxiety and feel empowered throughout a healthcare journey.

Schedule Your Pulmonary Function Test at Belmar Cardiopulmonary Diagnostic Center

For patients in the Bellevue, WA area, Belmar Cardiopulmonary Diagnostic Center offers a trusted, locally accessible option for pulmonary function testing. Every test is performed, overseen, and interpreted by licensed, credentialed staff and board-certified physicians, all within a comfortable, non-clinical atmosphere that patients often describe as feeling more like a living room than a typical medical office.

BCDC provides a comprehensive range of PFT services, including spirometry, diffusion capacity, methacholine challenge, FeNO testing, and exercise challenge testing. With flexible scheduling that includes weekends and significantly reduced wait times compared to many regional facilities, patients spend less time waiting and more time getting answers. Backed by a quality-over-quantity philosophy and 21+ years of experience, the team is committed to caring for each patient with dignity and genuine attention.

To schedule an appointment or ask questions, call 206-730-9364, email hello@belmarcardio.org, or use the online contact form. At BCDC, patients are never just a number. They are cared for with compassion, respect, and a real investment in their long-term health.