I'm not sure how the CAA measure Hb, my Class 2 medical involved some sort of fingerprick test. It that's the case, it's probably worth having a re-test involving taking a sample from your arm.
If your talking in units of g/dl, then I suspect the 0.1 difference is due to an artefact, rather than anything sinister.
Anaemia is usually seen as a symptom, rather than a disease, and your doc. is duty bound to differentiate between the various causes.
The likely cause, and further investigations, will depend on your age, sex, and co existing health.
The most (common), and most benign cause is heavy periods, the most unlikely (and sinister) cause is cancer. And there's lots of mid ground inbetween.
So go and see someone who knows what they are talking about. Your GP is a good starting point.
And what the flipp are the CAA doing measuring Hb's? Are they trying to stop planes crashing, are they interested in saving pilots live's, or have they just got a new machine to play with?