How Pulmonary Function Tests Guide Pulmonary Disease Treatment: Reading Your Spirometry Report

The envelope arrives before the appointment does. Inside, a single printed sheet: two curves that look like a fishing hook and a lopsided hill, a grid of abbreviations, and a column of percentages that could just as easily belong to a mortgage statement. FEV1, 68% pred. FEV1/FVC, 0.64. Post-BD change. You read it twice in the parking lot and understand none of it, except that some of the numbers are lower than others, and lower feels bad.

That sheet is one of the most useful documents in respiratory medicine, and also one of the least explained. Spirometry is the breathing test in which you blow as hard and long as you can into a mouthpiece while a machine measures how much air moves and how fast. Done well, it tells your clinician whether your airways are narrowed, whether your lungs are stiff or small, and how much either has changed since last time.

This guide walks through pulmonary function test results explained the way a good pulmonologist would across a desk: which numbers carry weight, which are noise, and how each one nudges a treatment decision in one direction or another.

What actually happens during a spirometry test?

Spirometry is closer to an athletic effort than a blood draw. You sit upright, a soft clip pinches your nose shut so no air escapes, and you seal your lips around a disposable mouthpiece attached to a small flow sensor. The technician asks you to breathe normally, then fill your lungs completely, then blast the air out as hard and as fast as you can and keep pushing until you feel empty. Six seconds of forced exhalation is the usual target for adults; it feels far longer than it sounds.

One blow is never enough. According to the NHS, you will typically be asked to repeat the maneuver at least three times so the lab can confirm the results are consistent, because a half-hearted or coughed-through effort produces numbers that look like disease when the lungs are fine. Technicians are trained to coach loudly and cheerfully for this reason. The performance matters as much as the machine.

Preparation is simple but not trivial. Most labs ask you to avoid smoking, vigorous exercise, large meals and alcohol for several hours beforehand, and to wear loose clothing that lets your chest and belly expand. Some clinicians ask patients to hold a specific inhaler before the test so a “before and after bronchodilator” comparison is meaningful. That instruction comes only from your prescribing team, and only for the test window; never pause a prescribed medicine on your own initiative.

A basic spirometry session takes around 30 to 90 minutes including setup and repeats, per NHS guidance. If your clinician has ordered full pulmonary function testing, you may also sit inside a clear booth (a body plethysmograph) that measures the total volume your lungs can hold, and breathe a harmless trace gas mixture that measures how efficiently oxygen crosses from the air sacs into the blood. Those additions are explained further down.

Pulmonary function test results explained: the numbers on the page

Most spirometry reports print five to seven values, each with three columns: your measured result, the predicted value for someone of your age, sex, height and ancestry, and your result as a percentage of that prediction. The percentage is the one to read first, because raw liters mean little without context. A 6-foot-3 former rower and a 5-foot-1 retiree will have wildly different “normal” volumes.

Here are the core terms, each defined once:

• FVC (forced vital capacity): the total amount of air you can blow out after the deepest breath you can take. It is a measure of lung size and chest mechanics.
• FEV1 (forced expiratory volume in one second): how much of that air comes out in the first second. Narrow airways slow the exit, so FEV1 drops when airways are obstructed.
• FEV1/FVC ratio: the fraction of your total exhaled air that leaves in the first second. Healthy adults empty most of their lungs quickly; obstructed airways cannot.
• PEF (peak expiratory flow): the single fastest moment of airflow. Useful for tracking asthma at home, but effort-dependent and rarely decisive in a lab report.
• FEF25-75: average flow across the middle half of the exhalation. It reflects smaller airways but varies so much between efforts that Cleveland Clinic and other centers advise against reading too much into it alone.

Two curves accompany the numbers. The flow-volume loop plots speed against volume and, in obstruction, develops a scooped or “sagging” descent after the peak. The volume-time curve shows how quickly the lungs empty; a lazy, prolonged tail is a visual fingerprint of airflow limitation. Clinicians often glance at the loop before reading a single digit, because its shape flags both disease patterns and poor effort in a second.

What is the most important number on a pulmonary function test?

Ask three pulmonologists and you will get one answer with two footnotes. The answer is the FEV1/FVC ratio, because it decides the first fork in the interpretive road: is this obstruction or not? The footnotes are FEV1 percent predicted, which grades how severe the obstruction is, and FVC percent predicted, which points toward restriction when the ratio is normal but the volumes are small.

The logic is mechanical. When bronchial tubes are narrowed by inflammation, mucus or muscle spasm, air still leaves the lungs but it leaves slowly. Total volume (FVC) may be nearly preserved while the first-second volume (FEV1) falls, so the ratio between them drops. When the problem is instead a stiff lung or a restricted chest wall, both numbers shrink together and the ratio stays normal or even rises. That is why the ratio, rather than any single volume, sorts patients into the two broad families of lung disease.

Which number matters most for treatment depends on the family you land in. In asthma and chronic obstructive pulmonary disease (COPD), FEV1 is the value clinicians follow over years, because international COPD guidelines summarized in NIH patient resources grade severity by FEV1 percent predicted, and a steady FEV1 decline is a signal that a plan needs revisiting. In interstitial lung disease, where scarring stiffens the tissue, FVC and the diffusing capacity carry more weight than FEV1.

One caution about hierarchy. A single “most important” number invites people to fixate on it. A report with a borderline ratio, an FEV1 of 79 percent and a patient who has never been short of breath is not a diagnosis; it is a prompt for a conversation. The Mayo Clinic notes that spirometry results are always interpreted alongside symptoms, history and often imaging, never in isolation. Your treating team weighs the whole page, then the whole person.

What is a normal score for a pulmonary function test? Understanding percent predicted

There is no universal “normal” liter count, which is why reports convert everything to percent of predicted. Prediction equations are built from large populations of healthy nonsmokers and adjusted for age, sex, height and ancestry. Your result is then expressed as a percentage of what a healthy person matching those variables would typically produce.

By long convention, Cleveland Clinic and other centers describe FEV1 and FVC values of roughly 80 percent of predicted or above as generally within the normal range, with numbers above 100 percent being common and unremarkable. For the FEV1/FVC ratio, the fixed threshold used in COPD guidelines and cited in NIH resources is 0.70 (sometimes printed as 70 percent): a ratio below that suggests obstruction.

Modern labs increasingly add a second yardstick called the lower limit of normal (LLN), often printed alongside a z-score. The LLN marks the bottom 5 percent of the healthy reference population, so a value below it is statistically unusual regardless of the round-number cutoff. This matters at the edges of life. The fixed 0.70 ratio tends to over-label healthy older adults as obstructed, because the ratio drifts down naturally with age, and it can miss early disease in younger people whose “normal” ratio would be much higher. When a report shows a ratio of 0.68 in a 78-year-old with no symptoms, the LLN column is where an experienced reader looks next.

Ancestry adjustments deserve a plain word. Historically, equations applied different predicted values to different racial groups, a practice now under active revision by respiratory societies because it can understate disease in some populations. If your report mentions “race-neutral” or “GLI global” equations, that is the reason. Ask your clinician which reference set was used; it can shift a borderline percentage by several points without your lungs changing at all.

What is a bad FEV1 score? How severity is graded

“Bad” is the wrong frame, but the question behind it is fair: at what point does a low FEV1 start changing what a clinician does? The honest answer is that FEV1 is a dial, not a switch, and its meaning depends on whether obstruction is present at all.

If the FEV1/FVC ratio is normal, a low FEV1 usually just reflects a low FVC and points toward restriction, not toward a “bad” airway score. If the ratio is reduced, FEV1 percent predicted becomes the severity gauge. International COPD guidelines, as summarized in NIH patient information, band it roughly as follows: 80 percent or above is mild airflow limitation, 50 to 79 percent is moderate, 30 to 49 percent is severe, and below 30 percent is very severe. Asthma guidelines use similar language but lean more on how variable the numbers are over time and how much they improve after a bronchodilator.

What those bands do and do not tell you matters. FEV1 correlates only loosely with how breathless a person feels day to day; two people with an identical 55 percent can lead very different lives depending on fitness, body weight, other conditions and how well their airways respond to treatment. FEV1 does track more closely with long-term risk and with how frequently flare-ups occur, which is why clinicians follow it over years rather than reacting to one reading.

A single low value is also not a verdict. Effort, technique, a recent cold, or testing during an exacerbation can all depress FEV1 temporarily. The Mayo Clinic notes that clinicians commonly repeat spirometry when a result does not fit the clinical picture. When the number is confirmed and stable, it becomes a baseline. When it is falling faster than the slow decline expected with normal aging, that trend, more than the absolute figure, is what prompts a treatment review by the treating team.

Obstructive vs restrictive pattern: what the FEV1/FVC ratio meaning tells your doctor

Nearly every interpretation begins by sorting the report into one of two patterns, sometimes both. Obstruction means air gets out slowly because the tubes are narrow. Restriction means the lungs cannot fill fully because the tissue is stiff, the chest wall is limited, or the breathing muscles are weak. The table below shows how the main numbers typically behave in each, using the thresholds described by Cleveland Clinic and NIH resources.

Measure	Plain meaning	Obstructive pattern	Restrictive pattern
FEV1/FVC ratio	Share of air out in first second	Reduced (often below 0.70 or LLN)	Normal or increased
FEV1 % predicted	Speed of emptying	Reduced; grades severity	Reduced in step with FVC
FVC % predicted	Total air blown out	Normal or mildly reduced	Reduced (often below 80%)
Total lung capacity	Air lungs hold when full	Normal or increased (air trapping)	Reduced; confirms restriction
Diffusing capacity (DLCO)	Gas transfer to blood	Low in emphysema, normal in asthma	Low in lung scarring, normal in muscle or chest-wall causes
Flow-volume loop shape	Visual fingerprint	Scooped, sagging descent	Tall, narrow, “witch’s hat”

Conditions that commonly produce obstruction include asthma, COPD and bronchiectasis. Restriction is seen with pulmonary fibrosis and other interstitial lung diseases, severe scoliosis, neuromuscular conditions and, in some people, marked obesity limiting chest expansion. A mixed pattern is possible and requires lung volumes to untangle.

One trap deserves emphasis: spirometry can suggest restriction but cannot confirm it. A low FVC with a normal ratio can also result from severe air trapping in COPD, where stale air stuck in the lungs leaves less room to inhale. Only a total lung capacity measurement resolves the question, which is why your clinician may order the booth test before naming a pattern.

What does the bronchodilator response on a spirometry report mean?

Many reports carry two full columns of numbers labeled “pre” and “post,” separated by a wait of roughly 15 minutes during which you inhaled a short-acting bronchodilator, a class of medicine that relaxes the muscle wrapped around the airways. The test asks a single question: how much of this narrowing is reversible right now?

The answer is expressed as the absolute change in FEV1 (in milliliters) and the percentage change from the pre-test value. Labs apply a threshold based on both numbers together, printed on the report, above which the response is called “significant.” The dual criterion exists because a small lung can show a big percentage change from a trivial volume, and a large lung can gain a lot of milliliters that amount to a small percentage.

A clearly significant response, especially one that lifts the ratio back into the normal range, supports a diagnosis of asthma, where airway narrowing is by definition variable. A minimal response with a persistently low ratio fits COPD, where much of the narrowing comes from structural damage that muscle relaxation cannot undo. Reality is messier than that binary. The Mayo Clinic notes that people with COPD can show meaningful reversibility, and people with asthma can test flat on a good day or after years of remodeling. A single bronchodilator test therefore refines, rather than settles, the diagnosis.

Two interpretive points follow. First, a “negative” bronchodilator test does not mean a bronchodilator will not help you; it measures airflow at one moment, not symptom relief or flare-up prevention over months. Second, if you used your usual inhaler shortly before testing because no one told you to hold it, the pre-test numbers may already be “post” and the response will look blunted. Tell the technician exactly what you took and when; it changes how the report is read.

Pulmonary function test results explained beyond spirometry: lung volumes and DLCO

Spirometry measures only the air you can move. It says nothing about the air left behind after a full exhalation, nor about whether oxygen is actually crossing into the bloodstream. Two additional tests fill those gaps, and their results often reshape the story the spirometry told.

Lung volume measurement, usually done by body plethysmography in a clear booth or by a gas-dilution method, produces total lung capacity (TLC, all the air the lungs hold when full) and residual volume (RV, the air that stays after you blow everything out). In COPD and severe asthma, both often rise: air becomes trapped behind narrowed airways, the chest hyperinflates, and the diaphragm flattens into a less efficient shape. That trapping explains why some people with a modestly reduced FEV1 feel disproportionately breathless. In restrictive disease, TLC falls, and per Johns Hopkins Medicine this is the finding that confirms restriction rather than merely suggesting it.

Diffusing capacity for carbon monoxide (DLCO) works differently. You inhale a gas mixture containing a tiny, harmless trace of carbon monoxide, hold your breath for about ten seconds, and exhale; the machine measures how much was absorbed. Because carbon monoxide binds avidly to blood, the amount taken up reflects the health of the membrane between air sacs and capillaries and the volume of blood flowing past. DLCO drops when that membrane is destroyed (emphysema), thickened by scarring (pulmonary fibrosis) or starved of blood flow (pulmonary vascular disease). It typically stays normal in asthma and in restriction caused by weak muscles or a stiff chest wall.

Put together, these tests let a clinician distinguish two people with identical spirometry. An obstructed report with a low DLCO points toward emphysema; the same report with a normal DLCO fits asthma or chronic bronchitis. A restrictive report with a low DLCO suggests disease within the lung tissue; with a normal DLCO, the problem is likely outside it.

How to read spirometry results with your doctor and turn them into a treatment plan

Numbers do not treat anyone. What they do is narrow the field of likely diagnoses, set a severity baseline, and create a yardstick for judging whether a plan is working. Here is how that translates across the common lung conditions, in general terms and always subject to your treating team’s judgment.

In asthma, spirometry establishes variable obstruction, and the bronchodilator response supports the diagnosis. Guideline-based treatment centers on inhaled corticosteroids, a class of medicine that dampens airway inflammation over weeks rather than minutes, often paired with bronchodilators that open the airways. Repeat spirometry months later is used to confirm that FEV1 has recovered toward the person’s best and that the ratio has normalized; a persistently low FEV1 despite good adherence is a prompt to look for triggers, check inhaler technique, or reconsider the diagnosis.

In COPD, the FEV1 band helps stratify risk, but current international guidance emphasized in NIH resources weighs symptoms and flare-up history at least as heavily when choosing among long-acting bronchodilator classes and deciding whether to add an inhaled corticosteroid. Spirometry also identifies candidates for pulmonary rehabilitation, an exercise and education program with robust evidence for improving breathlessness and daily function, and a low DLCO with hyperinflation can flag people who may be assessed for procedures that reduce trapped air.

In interstitial lung disease, a falling FVC or DLCO across serial tests is one of the main signals that disease is progressing and that antifibrotic medicines, a class that slows scar formation, may be considered by a specialist team. In neuromuscular disease, declining volumes measured lying down can guide timing of breathing support.

Across all of these, the pattern is the same: the test defines the starting line and marks each lap. It never issues the instructions on its own.

Who is usually tested, and who is usually asked to wait?

Spirometry is ordered for two broad reasons: to investigate symptoms and to monitor a known condition. Common triggers for a first test include breathlessness on exertion that outpaces age and fitness, a cough persisting beyond eight weeks, wheeze, a history of smoking or occupational dust exposure, and unexplained low oxygen readings. MedlinePlus lists asthma, COPD, pulmonary fibrosis and workplace lung disease among the conditions the test helps evaluate. People with an established diagnosis are typically retested at intervals set by their clinician, and many are tested before major surgery to gauge how their lungs will tolerate anesthesia.

Children can perform spirometry reliably from around school age with patient coaching, and the test is a standard part of pediatric asthma care. Very young children and people with significant cognitive impairment may not manage the coordinated forced blow, in which case clinicians rely on history, examination and other measures.

Some people are asked to postpone. Because the forced maneuver sharply raises pressure inside the chest, head and abdomen, Cleveland Clinic and other centers advise delaying the test after a recent heart attack or unstable angina, recent chest, abdominal, eye or brain surgery, a recent collapsed lung (pneumothorax), a known aneurysm, or an active respiratory infection that would both distort results and expose staff to infection. Severe uncontrolled blood pressure is another reason to wait. Coughing up blood of unknown cause usually prompts imaging first.

Timing also affects interpretation rather than safety. Testing during or just after a chest infection or asthma flare captures the lungs at their worst and can make a stable condition look far more severe than it is. Many clinicians prefer to wait several weeks after an exacerbation before establishing a baseline, so a delayed appointment is often a deliberate choice rather than an inconvenience.

What the following days and weeks usually look like after your test

The test itself leaves nothing to recover from. A few people feel lightheaded or notice a headache for a short while after repeated hard blows, and those with asthma occasionally feel tight-chested; both typically settle within minutes, and the lab will keep you seated until you feel steady. If a bronchodilator was given, a brief fluttery or jittery feeling is a recognized and short-lived effect of that class of medicine.

The report usually reaches your ordering clinician within a few days, and many labs release it to patient portals at the same time, which is precisely how people end up staring at unexplained percentages in a parking lot. A preliminary machine-generated interpretation is often printed on the sheet. Treat it as a draft. Automated readings apply fixed cutoffs without knowing your symptoms, your effort or your history, and the final interpretation is the one your clinician signs.

What happens next depends on the pattern. A normal result in someone with symptoms often leads to other investigations, because spirometry does not detect every lung problem and does not assess the heart, which is a frequent cause of exertional breathlessness. An obstructive pattern with a significant bronchodilator response commonly leads to an asthma-focused plan and a repeat test after a few months of treatment to confirm the lungs have responded. An obstructive pattern without reversibility, or any restrictive pattern, usually prompts full lung volumes and DLCO if not already done, and often imaging such as a CT scan.

Monitoring intervals vary. People with stable COPD or asthma are often retested roughly once a year, per typical guideline practice described in NHS resources, while those with interstitial lung disease may be tested every few months while a specialist team judges whether the disease is progressing. Your clinician sets the cadence; the test’s value grows with each point on the trend line.

What people often get wrong about spirometry test results interpretation

“A low number means I have COPD.” A low FEV1 alone does not. Obstruction requires a reduced FEV1/FVC ratio; a low FEV1 with a normal ratio points elsewhere, and a low ratio can reflect asthma, bronchiectasis or, in older adults, simply age when the fixed 0.70 cutoff is applied without checking the lower limit of normal.

“My percentage is my lung function.” Percent predicted compares you to a statistical average of healthy people your size and age, not to your own peak. Someone who started life with unusually large lungs can lose a considerable amount and still read 90 percent. Trend over time, measured on the same equipment, tells you more about your lungs than any single comparison to a population.

“The bronchodilator test showed no response, so inhalers are pointless.” The test measures airflow change over about 15 minutes. It does not measure how a person feels over months, how often they flare, or how their airways respond to anti-inflammatory treatment, which works on an entirely different timescale. Decisions about inhaled medicines rest with the prescribing clinician, informed by far more than one pre-post comparison.

“I can practice and improve my score.” Technique matters enormously, but only in one direction. Poor effort makes healthy lungs look diseased; no amount of effort makes diseased lungs look healthy, because the limit is physical. Good coaching removes false lows; it does not create false highs. This is also why a single result that seems too bad to be true is repeated rather than believed.

“A normal spirometry means my lungs are fine.” Spirometry can miss early emphysema, small-airway disease, pulmonary vascular disease and problems with gas transfer. A normal report in someone with real symptoms is a reason to keep looking, often with DLCO, imaging or cardiac assessment, not a reason to stop.

Questions to ask your care team about your pulmonary function test

A good consultation about a spirometry report is a two-way exchange. Bringing a short list keeps the conversation anchored in your numbers rather than in general reassurance. These are the questions experienced clinicians tend to welcome.

• Which pattern does my report show, obstructive, restrictive, mixed or normal, and which specific values led you to that reading?
• Were my results compared to the fixed cutoff, the lower limit of normal, or both, and which reference equations did the lab use?
• Was my effort and consistency graded as acceptable, and should any of these numbers be repeated before we rely on them?
• How does this compare with my previous tests, and is the rate of change what you would expect for my age?
• Did the bronchodilator response change how you interpret the result, and did the timing of my usual inhalers affect it?
• Do I need lung volumes, a diffusing capacity test or imaging to confirm the pattern, and what would each add?
• Which of these numbers will you follow over time to judge whether my current plan is working, and what change would prompt a rethink?
• How often should I be retested, and should I try to have it done on the same equipment each time?
• Are there other explanations for my symptoms, including my heart or fitness, that this test cannot see?
• Is there anything in these results that changes what I should do before surgery, during travel, or at altitude?

Ask for a copy of the full report including the curves, not just the summary line, and keep it. Serial reports laid side by side are among the most informative documents you can bring to any future appointment, especially if you move or change clinicians. If a term on the sheet is unfamiliar, ask for its one-sentence meaning; clinicians who read these daily sometimes forget the abbreviations are not universal.

When to call your doctor

Spirometry is a planned, low-risk test, and most people leave the lab feeling exactly as they arrived. Still, two situations warrant contact with your clinical team, one about the test itself and one about the condition it is investigating.

After the test, get in touch the same day if you develop chest tightness or wheeze that does not settle within a short rest, a headache that worsens rather than fades, or dizziness that persists after you have been seated and hydrated. Call urgently, or seek emergency care, if you notice sudden sharp chest pain with breathlessness, especially on one side, since the forced maneuver can very rarely provoke a pneumothorax in vulnerable lungs; if you cough up blood; or if your lips or fingertips take on a bluish tint.

Independent of the test, anyone under investigation for lung disease should seek urgent help for breathlessness so severe that speaking in full sentences is difficult, a rescue inhaler that brings no relief, confusion or drowsiness alongside breathing difficulty, chest pain spreading to the arm, neck or jaw, a fever with rapid breathing and a productive cough, or oxygen saturation readings on a home device that fall well below your usual baseline. New swelling of one leg with breathlessness is a red flag for a blood clot and needs same-day assessment.

Less dramatic changes also deserve a call rather than a wait for the next scheduled visit: a steady increase in how often you need a reliever inhaler, waking at night breathless, a cough lasting beyond eight weeks, unexplained weight loss, or a noticeable drop in what you can do compared with a few months ago. Your treating team would rather review an early change than a late one, and every decision about testing, medicines and follow-up remains theirs to make with you.

Frequently asked questions

How do I read my pulmonary function test results?

Start with the FEV1/FVC ratio to see whether airways are obstructed, then check FVC percent predicted for possible restriction, then use FEV1 percent predicted to grade severity if obstruction is present. Look at the post-bronchodilator columns for reversibility and at the flow-volume loop shape. Treat the printed automated interpretation as a draft; the final reading belongs to the clinician who knows your history, symptoms and previous tests.

What is a bad FEV1 score?

There is no single bad score, because FEV1 means different things depending on the ratio. When obstruction is present, international COPD guidance bands FEV1 percent predicted as mild at 80 and above, moderate at 50 to 79, severe at 30 to 49 and very severe below 30. A low FEV1 with a normal ratio points to restriction instead. One reading can also be depressed by effort or a recent infection and is usually repeated.

What is a normal score for a pulmonary function test?

FEV1 and FVC at or above roughly 80 percent of the predicted value for your age, sex, height and ancestry are generally read as normal, and an FEV1/FVC ratio of 0.70 or higher, or above the lower limit of normal, argues against obstruction. Values over 100 percent are common. Labs increasingly print a lower limit of normal and z-score, which are more accurate than fixed cutoffs in older and younger people.

What is the most important number on a pulmonary function test?

The FEV1/FVC ratio, because it determines whether the pattern is obstructive or not, which is the first decision in every interpretation. After that, FEV1 percent predicted grades obstruction severity and is followed over years in asthma and COPD, while FVC and diffusing capacity carry more weight in scarring lung diseases. No single number is interpreted without the others, your symptoms and often imaging.

What is the FEV1/FVC ratio meaning in plain terms?

It is the share of your total forced breath that you can blow out in the first second. Healthy airways let most of the air out fast, so the ratio is high. Narrowed airways slow the exit, so a smaller fraction leaves in that first second and the ratio falls. A reduced ratio therefore signals airflow obstruction, while restriction from stiff lungs typically leaves the ratio normal or raised because both volumes shrink together.

Is a normal FEV1 percentage the same for everyone?

No. The percentage compares your measured volume with a predicted value calculated from your age, sex, height and ancestry using large reference populations, so the liters behind an 85 percent result differ widely between people. Predicted values also fall gradually with age. Because you are compared with a population rather than with your own earlier best, a change across your own serial tests is often more informative than the percentage itself.

Can spirometry tell the difference between asthma and COPD?

It helps but rarely settles it alone. A significant improvement in FEV1 after a bronchodilator, especially one that normalizes the ratio, supports asthma, while fixed obstruction with minimal response fits COPD. Some people with COPD show reversibility and some with long-standing asthma do not, and the two can coexist. Clinicians combine spirometry with symptom history, exposure history, diffusing capacity and sometimes imaging or allergy testing.

Why did my doctor order lung volumes and a DLCO test as well?

Because spirometry only measures air you can move and cannot see trapped air or gas transfer. Total lung capacity confirms or rules out restriction and reveals hyperinflation in COPD, while DLCO shows how well oxygen crosses into the blood. Together they distinguish emphysema from asthma when spirometry looks identical, and separate lung tissue scarring from restriction caused by chest wall or muscle problems.

Should I stop my inhaler before a spirometry test?

Only if your prescribing clinician or the testing lab specifically instructs you to, and only for the window they specify. Holding a bronchodilator can make the pre- and post-bronchodilator comparison meaningful, but pausing any medicine is a decision for the team that prescribed it, not something to do on your own. If you did use an inhaler before the test, tell the technician exactly what and when so the report is read correctly.

How often should spirometry test results interpretation be repeated?

It depends on the condition and how stable it is. People with stable asthma or COPD are often retested roughly once a year or after a change in treatment, while those with interstitial lung disease may be tested every few months so specialists can judge progression. A result that seems inconsistent with symptoms is usually repeated sooner. Your clinician sets the interval, ideally on the same equipment for a reliable trend.

References

• NHS: Spirometry
• Cleveland Clinic: Pulmonary Function Testing
• NIH National Heart, Lung, and Blood Institute: COPD Diagnosis

This article is for general information only and is not a substitute for professional medical advice. Please consult a qualified doctor about your individual situation.