Spirometry for asthma diagnosis

[Dilbertian]

I was diagnosed with asthma by peak flow readings and trial of treatment. It's generally well-controlled, except when I catch a cold.

No spirometry was done, because of the pandemic. Now the lists are open again and the Asthma nurse has referred me for spirometry. Good. But if I'm well at the time, what will it show?

I think it would show if there was something else contributing. I have compromised lung function due to some mystery small airways disease and was put on a steroid inhaler for that. Spirometry revealed it - I don't have classic asthma and it was only due to the spirometry that the doctor finally believed I wasn't making it all up.

DD's shows even when well, she's very fit too (her peak flow is well above expected when well) but her asthma always shows with spirometry.