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British Lung Foundation
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Why not just fev1 to diagnose?

Why not just fev1 to diagnose?

I read all the time where they use the fev1 and fvc ratio to diagnose copd. So, call me dumb, but if fev1 tells what stage of copd you are in, then why do they need to use any other numbers to show/diagnose severity? Can't it be as simple as the fev1 level to validate you have it AND at what level you are..... period? Plain and simple? :o hmmm.....

P.S. I'm still learning. hahahaha!! Be gentle.

6 Replies


FEV May tell you the severity

FEV/FVC will tell whether you have restrictive lung condition or a obstructive lung condition

COPD is a obstructive condition.plus others

Idiopathic pulmonary fibrosis is restrictive condition plus others

If your FEV and FVC are normal or above, the FEV/FVC ratio is ignored.


Gotcha'!! I understand a bit more now. I haven't googled a lot, so that I won't freak out about the things I read. :(

However I will ask questions here. So thank you for that answer.

So the fev/fvc ratio can mean different things/different diagnosis/different everything.

Thanks stone-UK! :)


There are other numbers that tell you how much air trapping you have and also how well your lungs are able to transfer oxygen to the blood.


I agree with the whole ratio nonsense it is the same for asthma I tend to show strong reversibility and low fev1 also sometimes hyperinflation but because my ratio didn't show much according to cons everything else got dismissed and this was taking into account 4 sets of lung function tests over several years



Fev only measures the amount of obstruction but strangely not all conditions classed as c.o.p.d are obstructive in nature. c.t. scans and D.L.C.O shows I have severe emphysema with a loss of over 60% of my lung surface area, yet my fev is at 110% expected, I have no other related conditions and no measurable obstuction, the occasional DLCO tests done at the hospital show my condition deteriorating slowly but my spirometry nurse says if she did not know I had emphysema she wold say from my F.E.V results that I have no copd at all ! and I am not the only person in this position.

Contrary to your question I think we should ask if spirometry should be used at all to measure the severity of lung disease.

IF spirometry were the only measure I and many others would still be undiagnosed!.


Fev1 (Forced Expiry Volume) is the volume of air that you can forcibly blow out in 1 second.

FVC (Forced vital capacity) is the volume of air that can forcibly be blown out after full inspiration.

Normal = should be able to blow 70-80% (arguable) of your total (FVC) capacity in 1 second.

Fev 1 is measured in litres ( so 2 or 3 or thereabout). If big number 25, 40, 60, 80 etc that is % of predicted (expected from 'normal lungs' of a person your height, age & gender).

Men have significantly bigger lungs, and so different norms, than women.


Predicted numbers is an average of normals of your sex, that include big people with small lungs and small people with big lungs.

So taken by itself Fev1 could look 'obstucted' because your blow is less than average... but you could have smaller than average lungs thus actually be normal.

***Someone else could blow 90% predicted but have bigger than average lungs and actually be obstructed***

So they need to take into account the size of your own lungs hence the ratio of blow(FEV1) to volume (FVC) where Fev1 divided by Fvc (FEV1/FVC) = 75%, arguably, is bottom of the normal range, or top of the obstructed.. depending on age, and depending on history, smokers (&ex) with symptoms very likely to be deemed obstructed.

***So you can see it is not only possible to be obstructed if your both Fev1 & FVC is above predicted, it is more likely - ie if your fev1> predicted & FVC less than predicted the ratio(%) would be higher & show no obstructive pattern; whilst the bigger FVC, the lower the ratio and the worse the obstruction.

FEV1/FVC is the primary go-to measure in spirometry diagnosing or ruling out COPD .


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