PFT test explained — what it measures, how to prepare and what your report means

A PFT test — a pulmonary function test, also called a lung function test — is the breathing equivalent of an ECG. It turns a vague complaint like 'I get breathless on the stairs' into numbers that can be compared with normal values for your age, height, sex and ethnicity, and then tracked over time. If your doctor has ordered a PFT test, this is what to expect.

Why a PFT test is ordered

• Breathlessness or cough that has lasted more than three weeks
• To confirm asthma and demonstrate reversibility after a bronchodilator
• To confirm and grade COPD in a current or ex-smoker
• To monitor interstitial lung disease, post-tuberculosis or post-COVID lung damage
• Before major surgery, or as part of occupational and pre-employment health checks
• To decide whether treatment is working, before escalating medication

The three parts of a full PFT test

Spirometry measures the volume and speed of air you can blow out. Lung volumes (by body plethysmography or dilution) measure the air left behind that you cannot blow out, which separates restrictive from obstructive disease. Diffusion capacity (DLCO) measures how efficiently oxygen crosses from the air sacs into the blood — the number that falls early in emphysema and interstitial disease. Many patients only need spirometry; your pulmonologist decides how much of the panel is required.

How to prepare for a PFT test

• Avoid your reliever inhaler for 6 hours beforehand unless you are breathless
• Skip the morning dose of long-acting inhalers only if the clinic instructs you to
• No smoking for at least an hour, preferably 24 hours
• No heavy meal in the 2 hours before, and no strenuous exercise that morning
• Wear loose clothing; tight waistbands and tightly pinned saris limit a full breath
• Bring all your inhalers and any previous PFT, X-ray or CT reports

What happens during the test

You sit upright, a soft clip closes your nose, and you seal your lips around a mouthpiece. The technician coaches each manoeuvre loudly and specifically: breathe in as deep as you can, then blast the air out as hard and as long as possible. Three technically acceptable, reproducible efforts are needed — this is why the coaching matters more than the machine. If reversibility is being tested, you inhale a bronchodilator and repeat the blows after 15 minutes. The whole appointment takes 30–45 minutes, it is completely non-invasive, and there is no radiation. Mild dizziness or a brief cough is common and settles within seconds.

Tell the technician if you have had eye, chest or abdominal surgery recently, a heart attack in the last month, an active pneumothorax, or uncontrolled high blood pressure — these are reasons to postpone forced manoeuvres.

Reading your PFT report

• FVC — total volume you can forcefully exhale after a full breath in
• FEV1 — volume exhaled in the first second; the workhorse number
• FEV1/FVC ratio — below the lower limit of normal indicates obstruction
• Reversibility — a rise in FEV1 of 12% and 200 ml after bronchodilator supports asthma
• TLC and RV — total and residual volumes; a low TLC indicates restriction
• DLCO — gas transfer; reduced in emphysema, ILD and pulmonary vascular disease
• Z-scores or % predicted — how far you sit from normal for your demographics

In broad terms: obstruction with reversibility suggests asthma; fixed obstruction in a smoker suggests COPD; a restrictive pattern with a low DLCO suggests interstitial lung disease; and normal spirometry with a low DLCO points towards early emphysema or a vascular cause. A report also carries a quality grade — an ungraded or poorly reproducible test should be repeated rather than acted upon.

When a PFT test is not enough

Spirometry needs maximal effort, which children under six and some elderly or neurologically affected patients cannot deliver. Forced oscillation technique (FOT) requires only quiet breathing and gives airway resistance and reactance instead — useful for young children and for follow-up. Where symptoms are exercise-related but resting numbers are normal, a six-minute walk test with oxygen saturation monitoring, or bronchial provocation testing, is the next step.

Getting a PFT test in Coimbatore

At Lung Care — The Pulmonary Clinic in R.S. Puram, lung function testing is done in-house with technician coaching, and the report is interpreted by Dr. Arun Gangadhar during the same visit rather than handed over as a bare printout. Bring your previous reports so trends, not just single values, guide the plan.

To book a PFT test, or to have an existing report explained, book a consultation or call the clinic on +91 82203 33209.