A spirometry report is a page of numbers and a curve, handed over with about eight seconds of explanation. Here is what the numbers are.
The three that matter
FVC — forced vital capacity. The total volume of air you can blow out after taking the deepest breath you can. It is a measure of size.
FEV1 — forced expiratory volume in one second. How much of that total comes out in the first second. It is a measure of speed.
FEV1/FVC — the ratio between them. This is the one to read first, because it distinguishes between two very different problems.
If the ratio is low, air is coming out too slowly for the size of your lungs. Something is narrowing the airways: that is obstruction, and it points at COPD or asthma. If the ratio is normal or high but both numbers are small, the lungs are simply not holding much. That is a restrictive pattern, and it points somewhere else entirely — scarring, chest wall or muscle problems, sometimes weight.
Same breathlessness, opposite investigations. Which is why the ratio comes first.
What percent predicted actually means
Beside each number is a percentage. It is not a score out of a hundred.
Your result is being compared against the average for people who share your age, height, sex and ethnic background, because all four change what a healthy lung does. A 68-year-old man of 5 foot 7 is not expected to produce the same FEV1 as a 25-year-old of 6 foot 2, and the software accounts for that.
So 78% predicted does not mean your lungs are 78% functional. It means you produced 78% of what the reference population your size and age typically produces. Whether that is meaningful depends entirely on the ratio, on your symptoms, and on what your previous tests showed.
That last point is underrated. A single spirometry is a snapshot. Two of them, eighteen months apart, are a trend, and a trend is far more useful than any one reading.
The bronchodilator part
Often the test is done twice: once at baseline, then again after an inhaled bronchodilator.
The comparison answers a specific question — how much of the narrowing opens back up? Substantial improvement points toward asthma, where the obstruction is largely reversible. Obstruction that persists after the bronchodilator is what defines COPD.
Plenty of people show features of both, and that is a recognised situation rather than a contradiction in the report.
Why effort changes everything
Spirometry is one of the few tests where the patient can change the result by not trying hard enough, and it does not fail gracefully. A half-hearted blow produces a curve that looks like obstruction.
This is why the technician keeps shouting at you to keep going, why you repeat it several times, and why a good report notes whether the efforts were acceptable and repeatable. If your test was done once, quickly, with no coaching, it is fair to ask whether it should be repeated before any diagnosis is hung on it.
It is also why results are hard to interpret if you were unwell on the day, had just used your rescue inhaler, or were in pain from something unrelated.
What to ask
What was my FEV1/FVC ratio, and is it above or below 0.70? Is this an obstructive or a restrictive pattern? Were the efforts acceptable? Do you have a previous spirometry to compare it against? And if I was given a bronchodilator, how much did the numbers move?
Ask for a copy of the report. It is your result, it is one page, and having the previous one in hand is what makes the next one worth doing.