If you have been treated for a breathing problem for years without ever blowing into a machine, something important has been skipped. Spirometry is the test that turns "it is probably asthma" into a diagnosis, and it is the single most useful twenty minutes in respiratory medicine.
It is also widely avoided, usually because nobody has explained what it is.
What it measures
Spirometry measures how much air you can move and how fast you can move it. You take the deepest breath you can, then blow out as hard and as long as you possibly can into a mouthpiece. The machine records the shape of that breath.
Two numbers carry most of the meaning:
- FVC — forced vital capacity. The total volume you blew out.
- FEV1 — forced expiratory volume in one second. How much of it came out in the first second.
The ratio between them is what matters most. A healthy adult pushes out the large majority of their air in the first second. If the airways are narrowed, the air comes out more slowly, so FEV1 falls relative to FVC and the ratio drops. That is called an obstructive pattern, and it is the signature of asthma and COPD.
If instead the lungs are stiff or small, both numbers fall together and the ratio stays normal or rises. That is a restrictive pattern, and it points towards conditions like interstitial lung disease, or sometimes towards something outside the lungs entirely — obesity, a chest wall problem, muscle weakness.
The part that makes the diagnosis
The single measurement is useful. What actually separates asthma from COPD is doing it twice.
You blow, then you are given a bronchodilator — a reliever inhaler, usually salbutamol, through a spacer — and after about fifteen minutes you blow again.
- If the obstruction improves substantially, the narrowing is reversible. That is asthma.
- If it barely changes, the narrowing is largely fixed. That points to COPD.
- If the first test was normal, both become much less likely and the search moves elsewhere — reflux, post-nasal drip, a medication side effect, or something outside the airways.
This is why "spirometry with reversibility" is the phrase to look for, and why a single blow without the inhaler step answers only half the question.
What the appointment is actually like
No needles. No radiation. No dye, no sedation, no fasting. You sit in a chair and breathe.
A technician explains the manoeuvre and demonstrates it. You will usually wear a nose clip, so all the air goes through the mouthpiece. Then:
- Sit upright, feet on the floor.
- Breathe in as deeply as you can — all the way.
- Seal your lips around the mouthpiece.
- Blow out as hard as you can, immediately, and keep going.
- Keep blowing until told to stop. This is the hard part: six seconds feels like a long time, and most people stop too early on the first attempt.
You repeat it at least three times, because the test depends on your effort and the machine needs to see consistent results before it believes them. Being coached loudly is normal and is the technician doing their job.
Then the inhaler, a fifteen-minute wait, and three more blows.
The whole thing takes around twenty minutes, or thirty-five with the reversibility step.
How it feels
Light-headedness for a few seconds after a hard blow is common and passes. You may cough — that is normal, particularly if your airways are irritable. Some people feel briefly tired. Nothing hurts.
It is genuinely effort-dependent, which is its main weakness: a half-hearted blow produces a result that looks like disease. This is why it is repeated, and why a very poor-quality test should be repeated on another day rather than interpreted.
How to prepare
This is where most tests are spoiled, so it is worth getting right.
Medicines. You will usually be asked to hold your inhalers before the test, because the point is to see your airway in its untreated state. Typical guidance is to stop a short-acting reliever about six hours before, and long-acting inhalers for longer — but follow the instruction you are given, and never stop a medicine on your own. If you have had to use your reliever because you were breathless, say so; that is important information, not a reason to hide it.
On the day: avoid a heavy meal in the two hours before, no smoking for at least an hour, no alcohol, and no vigorous exercise in the half hour before. Wear clothing that does not restrict your chest or waist.
Bring: your inhalers, including the ones you have stopped using, your current medicine list, and any previous spirometry or chest X-ray reports. Comparison over time is often more informative than a single new result.
Tell them if you have had recent eye, chest or abdominal surgery, a recent heart attack, a collapsed lung, coughed up blood, or if you are pregnant. Spirometry raises pressure inside the chest and is postponed in some of these situations.
Who should have it
- Anyone with a cough lasting more than three weeks that has not been explained — see a cough that will not settle.
- Anyone treated for "asthma" who has never had it confirmed.
- Any smoker or ex-smoker over forty with a cough or breathlessness.
- Anyone breathless on exertion where the cause is not established — see breathlessness.
- Anyone having repeated courses of antibiotics for "chest infection". This article explains why that pattern usually is not infection.
- Anyone with an occupational dust or fume exposure and new respiratory symptoms.
- Children from about six, who can usually perform it reliably.
Reading your own report
You will be handed a sheet of numbers. Three things on it carry most of the meaning.
Per cent predicted. Your result is compared with what someone of your age, height, sex and ethnicity would be expected to produce. "FEV1 78% predicted" means you blew out 78% of the expected volume in the first second. Predicted values are population averages, so a healthy person can sit somewhat above or below 100%.
The FEV1/FVC ratio. This is the one that decides whether there is obstruction. Reported as a fraction or a percentage, a value below roughly 0.7 — or below the lower limit of normal for your age, which is the better standard — indicates obstruction. A normal ratio with both volumes reduced points instead towards a restrictive pattern.
The change after the inhaler. Reported as a percentage and an absolute volume. A meaningful improvement in FEV1 — conventionally around 12% and 200ml in adults — supports reversible obstruction, which is asthma.
Two cautions. A single reading slightly outside the predicted range is not a diagnosis; it is one piece of evidence beside your history and examination. And the test is effort-dependent, so a poor-quality blow produces a poor number. A good report says whether the quality criteria were met.
How often it should be repeated
For asthma or COPD that is stable, roughly once a year is usual, and sooner if symptoms change, treatment changes, or you have had an attack. The value is in the trend: a gradual fall over several years tells you something no single test can. This is why bringing old reports matters, and why it is worth keeping them.
Children and this test
Most children can do spirometry from about five or six years of age — earlier than many parents expect. What it needs is not lung strength but the ability to follow an instruction for six seconds, which is a matter of coaxing rather than capacity.
The equipment helps. Paediatric software turns the blow into a game on screen — candles to blow out, a balloon to inflate — and a child concentrating on putting out the last candle produces a far better effort than one being told to keep going. We allow extra time and more attempts for a first test, and it is normal for the first two or three blows to be unusable.
Below five, spirometry is usually not achievable, and the diagnosis rests on the pattern of symptoms, the response to a treatment trial, and examination. That is not a lesser approach; it is the accepted one at that age. Parents sometimes push for a test on the assumption that a number is more reliable than a clinical judgement, but a badly performed blow produces a misleading number, which is worse than none.
What it does not do
Spirometry does not diagnose infection, see a tumour or exclude a clot. It measures airflow. A normal result does not mean nothing is wrong — it means the problem is not airflow obstruction, which is itself useful. Where the question is about the lung tissue rather than the airways, fuller lung function testing with diffusion capacity measures how well oxygen crosses into the blood, and that is a different test.
Getting it done
Spirometry with reversibility is performed at Vaayu Care in Rewari, with the result explained in the same consultation rather than posted to you a week later — which matters, because the number means little without the history beside it.
Book a consultation, or call 8563816000 and ask for a breathing test.
Frequently asked questions
Does spirometry hurt?
No. There are no needles and no radiation. You breathe into a mouthpiece. A hard blow can leave you light-headed for a few seconds and may make you cough, but nothing hurts.
Should I stop my inhalers before the test?
Usually yes, and you will be given specific timings — commonly six hours for a reliever and longer for long-acting inhalers. Follow the instruction you were given and never stop a medicine on your own. If you had to use your reliever, say so rather than hiding it.
How long does it take?
About twenty minutes for spirometry alone, and roughly thirty-five with the reversibility step, which includes a fifteen-minute wait after the inhaler.
Can children do spirometry?
Most children can perform it reliably from about six years old. Below that, diagnosis rests on the symptom pattern, the family history and the response to a treatment trial with a review date.
My spirometry was normal but I still feel breathless. What now?
A normal result is informative: it makes asthma and COPD much less likely and moves the search elsewhere. Depending on the pattern, the next steps are usually a chest X-ray, blood tests for anaemia and thyroid, heart assessment, or fuller lung function testing with diffusion capacity.