A pulmonary function test result is considered “failed” when your breathing numbers fall outside the predicted normal range during spirometry, the standard test that measures how much air you can push out and how fast. Spirometry captures three values: FEV1 (forced expiratory volume in one second), FVC (forced vital capacity), and the FEV1/FVC ratio.
An abnormal result is data about your airflow, not a diagnosis on its own, and the next step is to figure out what your lungs are actually doing.
This guide walks through what an abnormal pulmonary function test really reveals about your breathing, from how spirometry numbers are read to what doctors do next.
What a Pulmonary Function Test Actually Measures
Spirometry, the core of pulmonary function testing, captures three numbers that tell the story of how your lungs move air. FEV1 is how much air you can blow out hard in the first second. FVC is the total amount of air you can force out after a full inhale. The FEV1/FVC ratio reveals the shape of your breathing pattern. A respiratory therapist or trained technician usually runs the test in a clinic or hospital pulmonary lab.
The core readings and the predicted baseline
Your results are compared against predicted values calculated from your age, height, sex, and sometimes ethnicity. FEV1 and FVC landing between about 80% and 120% of predicted typically count as normal.
A ratio below roughly 0.70 (or 70%) after a bronchodilator (a fast-acting inhaled medication that opens the airways) is the standard threshold the American Thoracic Society and European Respiratory Society use to flag obstruction, though a fixed ratio is now used alongside the lower limit of normal (LLN) to avoid misdiagnosis in older adults. Falling meaningfully below predicted is what most people mean when they say they failed the test.
Why doctors order PFTs in the first place
Preoperative clearance before major surgery, workplace screening for dust or chemical exposure, monitoring known conditions like asthma or COPD, and evaluating unexplained shortness of breath are reasons beyond diagnosing suspected lung disease that prompt clinicians to order PFTs. The test itself takes 30 to 45 minutes, though the actual breathing maneuvers take only a few minutes each. Most people get preliminary findings the same day, with a formal report typically arriving within a few days to a week.
| Reading | What it measures | Why it matters |
|---|---|---|
| FEV1 | Air blown out in the first second | Reflects how open your larger airways are |
| FVC | Total air forced out after a full inhale | Reflects overall lung volume and effort |
| FEV1/FVC ratio | Relationship between the two values | Distinguishes obstruction from restriction |
| DLCO (follow-up) | How well gas moves from lungs into blood | Detects early disease or vascular issues |
| Bronchodilator response | Change after inhaling a rescue medication | Tests whether obstruction is reversible |
The Two Patterns an Abnormal Result Can Reveal
Two distinct patterns account for almost every abnormal PFT, and identifying which one applies shapes every subsequent clinical decision. Obstruction means air has trouble getting out, while restriction means your lungs cannot fully fill with air in the first place. Sometimes both show up, and sometimes the numbers land in a gray zone that simply needs watching.
Obstructive patterns
A low FEV1/FVC ratio is the signature of obstruction, meaning air flows out of the airways more slowly than expected. Common causes include asthma, COPD (which includes emphysema and chronic bronchitis), bronchiectasis (permanent widening of the airways from chronic infection), and sometimes vocal cord dysfunction. The GOLD criteria (Global Initiative for Chronic Obstructive Lung Disease) further grade COPD severity using the FEV1 percent predicted, from mild (stage 1) through very severe (stage 4).
Restrictive patterns
A low FVC with a preserved ratio suggests restriction, where the lungs cannot fully expand. Causes range from interstitial lung disease (scarring of lung tissue) and pulmonary edema (fluid in the lungs) to obesity, kyphoscoliosis (a curved spine that limits chest expansion), and neuromuscular conditions such as muscular dystrophy or ALS. Chest wall disorders and prior lung surgery also fall into this category.
Mixed and borderline patterns
Some results show features of both obstruction and restriction, which usually points to combined disease and triggers deeper investigation. Mild abnormalities that fall just outside normal often get labeled borderline and may simply be monitored over time, especially when you feel well and have no risk factors. A single abnormal pattern is never a diagnosis on its own. Symptoms, history, physical exam, and imaging all have to fit before anything gets labeled.
When a “Failed” PFT Is Really a Testing Problem
A surprising number of so-called failed tests turn out to be failed efforts, meaning the readings were low because the maneuver was performed poorly rather than because the lungs were actually impaired. This is one of the most common reasons people walk out of a pulmonary lab convinced something is wrong, only to learn later the test simply needs to be repeated.
Heads up: a technician who sees a leaky seal, a half-hearted blow, or inconsistent effort will usually stop the test and coach you through it again before reporting anything as abnormal.
Poor effort is the single most common culprit. Not blowing hard or long enough, not inhaling fully before the forced breath, or stopping mid-blow all drag the numbers down. A leaky mouthpiece seal, a tongue or teeth obstruction, or a hesitant start can do the same thing. Coughing, dizziness, or anxiety mid-test can also cut the maneuver short.
Medication timing matters too: bronchodilators held beforehand can artificially worsen obstruction, while failure to hold them can artificially improve it and hide real disease.
- Poor effort: not blowing hard or long enough lowers every value.
- Leaks and obstructions: a loose seal, tongue, or teeth covering the mouthpiece distorts airflow.
- Incomplete inhalation: not filling the lungs fully before the forced breath shrinks FVC.
- Cough or dizziness: stopping the maneuver early makes the test technically invalid.
- Medication timing: not holding a bronchodilator when instructed can mask true obstruction.
How Doctors Read and Interpret Your Results
Interpreting a PFT is rarely a matter of glancing at one number. Your doctor layers your predicted range, your symptoms, your smoking history, and any occupational exposures onto the readings, then decides whether the picture is clear, borderline, or worth chasing further.
Comparing your numbers against predicted values
Most clinicians flag FEV1 and FVC that fall below about 80% of predicted and ratios that dip below roughly 0.70 as potentially abnormal. The American Thoracic Society and European Respiratory Society (ATS/ERS) guidelines emphasize using the lower limit of normal alongside fixed cutoffs, because a fixed 0.70 ratio can over-diagnose obstruction in older adults and under-diagnose it in younger ones.
Values inside 80 to 120% of predicted are generally reassuring, while readings well outside that range warrant a closer look.
Layering symptoms and history onto the numbers
A low FEV1 in a lifelong smoker with chronic cough and dyspnea (shortness of breath) points in a very different direction than the same low FEV1 in a young athlete with no symptoms. Doctors weigh age, smoking pack-years, occupational dust or fume exposure, family history of lung disease, and existing conditions like heart failure or reflux. That context is what turns a raw number into something meaningful for your situation.
Deciding on a bronchodilator reversibility test
After obstruction shows up on the initial tracing, the clinician typically moves to a bronchodilator reversibility test, asking the patient to inhale a rescue medication and then repeat the spirometry after a brief waiting period. A meaningful improvement in FEV1, typically at least 12% and 200 milliliters, supports a reversible process like asthma rather than a fixed one like emphysema. The National Heart, Lung, and Blood Institute (NHLBI) outlines this approach in its asthma care guidance.
The Next Steps After an Abnormal or “Failed” PFT
The path forward is usually a structured sequence of confirmatory tests, imaging, and possibly a specialist referral, rather than a single dramatic decision. Most cases move from initial concern to a clearer picture within days to weeks.
Confirm, then investigate
Most doctors start by repeating the PFT on a different day to confirm the result was not a one-off or a technique error. When obstruction is confirmed, a bronchodilator reversibility test is usually added. A chest X-ray or high-resolution CT scan can clarify whether structural changes (scarring, nodules, hyperinflation) are present.
When gas exchange is in question, an arterial blood gas (a blood sample from an artery measuring oxygen and carbon dioxide levels) or pulse oximetry may be ordered.
Specialist referral versus watchful waiting
Moderate to severe abnormalities, unclear patterns, or results that do not fit your symptoms usually trigger a referral to a pulmonologist (a lung specialist). Mild abnormalities in someone with no symptoms and low risk may simply be rechecked in several months. The decision is rarely urgent, but it should not be ignored. A confirmed abnormal PFT is information your lungs are offering, and acting on it early often changes the trajectory.
| Situation | Likely next step | Why |
|---|---|---|
| Mild abnormality, no symptoms | Repeat PFT in 3–6 months | Confirms whether the finding is stable or progressing |
| Obstruction confirmed | Add bronchodilator reversibility test | Distinguishes asthma from fixed obstruction |
| Unclear or mixed pattern | Chest imaging (X-ray or HRCT) | Looks for structural lung changes |
| Low oxygen or gas exchange concern | Arterial blood gas or oximetry | Measures how well the lungs oxygenate blood |
| Moderate to severe abnormality | Referral to a pulmonologist | Specialist evaluation for complex findings |
Retaking the Test and Improving Your Next Result
A poor first attempt is not held against you, and retesting is a normal, expected part of the process. Most PFTs can be repeated within days or weeks, and your next result is often dramatically better once technique issues are ironed out.
Practical preparation for a repeat test
Ask your doctor whether any medications should be held beforehand, especially short-acting bronchodilators, which are often paused for four to eight hours before testing for the most accurate numbers. Practice the forced breathing maneuver at home when you can: a full deep inhale, then a hard, fast blast of air that keeps going until your lungs are completely empty.
Avoid heavy meals, smoking, and intense exercise in the few hours before your appointment, since all three can affect your readings.
Tip: bring your previous results and a short list of your symptoms to the retest so the new readings can be compared directly and the technician knows what to look for.
Common reasons retests go better
Familiarity with the maneuver is the biggest factor. Once you know what a maximal effort feels like and how long the exhalation should last, performance tends to improve sharply. Coaching from the technician during the test, a properly sealed mouthpiece, and clearer instructions about when to stop all help. When your second test still comes back abnormal, the result is far more trustworthy, and that reliability is what lets your doctor move forward with confidence.
An abnormal pulmonary function test can feel alarming, and that reaction is normal. Most so-called failed tests reflect either a technical issue or a mild, reversible finding, and the path from an abnormal number to a clear plan is usually short, structured, and well within reach.
FAQ
Does failing a pulmonary function test mean I have a lung disease?
Not necessarily. An abnormal result means your numbers fell outside the predicted range, but a diagnosis requires matching the numbers to your symptoms, history, and often imaging or repeat testing. Many failed tests turn out to be testing errors rather than disease.
Can a pulmonary function test be wrong or inaccurate?
Yes. Poor effort, a leaky mouthpiece, coughing mid-test, or not holding certain medications can all produce falsely low readings. That is why technicians repeat maneuvers and why doctors confirm abnormal results on a separate day before drawing conclusions.
How long does it take to get pulmonary function test results?
You often hear preliminary findings the same day, with a formal interpreted report usually available within a few days to a week. Your ordering doctor reviews the report and explains what the numbers mean in context.
What conditions can an abnormal PFT detect?
Abnormal PFTs can point toward asthma, COPD, bronchiectasis, interstitial lung disease, pulmonary fibrosis, neuromuscular weakness affecting the diaphragm, and certain vascular conditions affecting gas exchange. The specific pattern guides which condition is most likely.
Should I be worried if I fail a spirometry test?
Mild concern is reasonable, but panic is not. Many initial failures are technique-related and resolve on retesting. When the abnormality is confirmed, early detection often leads to better outcomes, especially for conditions like asthma and COPD that respond well to early management.
What doctor should I see after an abnormal pulmonary function test?
Start with the doctor who ordered the test, usually a primary care physician. For moderate to severe abnormalities, unclear patterns, or suspected complex disease, a referral to a pulmonologist, a lung specialist, is the typical next step.
