Hi all,
The CAA medical looks for an FEV 1 of 80% with 70% being the lowest they'll accept and sign off there and then. Mine was just over 68 so they made me run round the car park and do the spirometry test again immediately and then after 10 minutes rest. They then had a specialist look at my results to see whether he thought I'd pose any kind of risk. Problem is I have a large lung capacity for my build (nearly 7 litres at 5"8) but only a regular sized tube to force it all out of.
The point is they have their margins but can do other tests if somethings not quite right.