Written for patients: what the scan can and cannot answer, the radiation involved, what to tell the team beforehand, and what the radiologist's report will say.

What Pulmonary shows

How the lungs work, measured rather than pictured. A pulmonary function test records how much air you can move, how fast you can move it, and in the fuller versions how well oxygen crosses from the air sacs into the blood. That functional answer is what separates asthma from COPD from a restrictive problem, and no image can give it. What the test cannot do is show you the lung: it will not reveal a nodule, a patch of pneumonia, a collapsed segment, fluid or a clot, and it says nothing about WHERE in the lung a problem sits. Those are questions for a chest X-ray or a CT chest, and in practice the function test and the picture are read together.

How it works, and what it feels like

You sit upright, a soft clip closes your nose, and you seal your lips around a mouthpiece so every breath goes through the machine. After a few normal breaths you take the deepest breath you can and blow out as hard, as fast and as long as you possibly can — usually at least six seconds, with the technician coaching loudly the whole way through, which is normal and necessary. The manoeuvre is repeated until three technically acceptable and reproducible efforts have been recorded. A bronchodilator is often then given through an inhaler and spacer and the whole set repeated about 15 minutes later, to see whether the airways open up. The test is entirely effort-dependent: a half-hearted blow produces an abnormal-looking result that reflects the effort rather than the lungs, which is why it is repeated rather than accepted first time.

Safety and radiation

There is no radiation, no injection and nothing to swallow — a lung function test only measures your own breathing, and it can be repeated as often as it is useful. The forced manoeuvre does raise the pressure inside the chest, the abdomen and the head sharply for a few seconds, and that is the reason the test is postponed after certain recent events rather than simply performed regardless. Feeling light-headed or coughing after a maximal blow is common and settles within a minute; tell the technician and they will let you recover fully before the next effort. Where imaging is done alongside the function test — a chest X-ray or a CT — that component carries its own radiation dose, described on those pages.

Who should not have a Pulmonary scan

Tell the team before your scan if any of these apply

Pregnancy: Spirometry itself involves no radiation, though a full forced manoeuvre in late pregnancy is often uncomfortable and less reliable. What matters is the imaging that frequently accompanies a respiratory workup: a chest X-ray or CT is deferred, shielded or replaced in pregnancy, and that decision is made by a doctor. Declare a pregnancy or the possibility of one when you book the appointment.
A recent collapsed lung, or recent surgery: The forced blow raises pressure inside the chest, the abdomen and the skull for several seconds, so the test is deferred after a pneumothorax and after surgery to the chest, abdomen or eye — commonly for at least a week, and longer after brain surgery. The exact interval is set by the doctor who requested the test, and it is a postponement rather than a refusal.
Recent heart attack, unstable chest pain or a known aneurysm: The same pressure change is the reason. A recent myocardial infarction, chest pain that is unstable, an uncontrolled rhythm disturbance, a recent pulmonary embolus not yet anticoagulated, or a known aneurysm in the chest, abdomen or brain all mean the test waits until the situation is stable. Mention any of these when booking rather than at the mouthpiece.
Coughing blood, or an active chest infection: Haemoptysis of unknown cause can be made worse by a forced manoeuvre, and an active transmissible chest infection — tuberculosis in particular — is aerosolised by it. The test is postponed until the cause is known or the infection is controlled, and where it must go ahead it is done with infection-control precautions and dedicated filters.
Being unable to perform or sustain the manoeuvre: A good seal on the mouthpiece and a sustained maximal effort are what the whole test rests on. Facial weakness, a recent stroke, severe breathlessness at rest, marked hearing impairment, confusion or dementia may make a reliable result impossible — and a poor technique yields a falsely ABNORMAL result rather than no result at all, which is the more dangerous outcome. Say so beforehand so a different assessment can be arranged.
Contrast, where the workup includes a CT: A CT pulmonary angiogram — the scan used when a clot on the lung is suspected — uses iodinated contrast, so kidney function, any previous contrast reaction and your medication list are all checked first, exactly as for any contrast CT. The function test itself needs none of this.

When a Pulmonary is ordered

Breathlessness on exertion, or at rest, of unclear cause
Diagnosing asthma and distinguishing it from COPD
Chronic cough, wheeze or chest tightness
Grading severity and checking the response to inhalers
Surveillance in dust, fume and chemical exposure at work
Assessment of respiratory fitness before major surgery
Monitoring interstitial lung disease and its treatment
Smoking and ex-smoking assessment from mid-life onwards

Contrast and preparation

A lung function test uses no contrast and no injection whatsoever. The only thing given is a bronchodilator, usually salbutamol through an inhaler and spacer, and only when reversibility is being assessed; it can leave a mild tremor or a faster heartbeat for a few minutes, which passes. What genuinely matters is the timing of your own medication: short-acting inhalers are withheld for around 6 hours and long-acting ones for longer ONLY if the requesting doctor has told you to, never on your own initiative, because the point is to measure the lungs without treatment on board. Avoid a heavy meal, smoking and vigorous exercise beforehand, and wear clothing loose enough not to restrict the chest and abdomen.

What your report will cover

The report gives each measured value alongside the value predicted for your age, height, sex and ethnicity, expressed as a percentage of predicted — the forced vital capacity, the volume blown out in the first second, the ratio between them, and the mid-expiratory flows. It states whether the pattern is normal, obstructive, restrictive or mixed, grades the severity, and reports the change after the bronchodilator with whether it meets the threshold for significant reversibility. A good report also grades how technically acceptable the effort was, because a poor-quality test should be repeated rather than interpreted. A spirometry pattern is never a diagnosis on its own: it is read together with your symptoms, your examination and your imaging.

How it works

The path from booking to results

Book in the app

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A phlebotomist visits home at your chosen time — or drop by a partner lab instead.

Processed at an NABL lab

Every sample is handled at one of our accredited labs, tracked end to end.

Report + doctor review

Your digital report lands with a complimentary read-through from a doctor.

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PFT (Pulmonary Function Test)

Pulmonary — what it shows, and who it is not for