@Mighi, the easy answer is to have something high glucose such as dextrose tablets, jelly babies, sweets such as mints, drink fruit juice, etc. All things that dissolve internally quickly and leave no trace to show up on a CT PET scan - which is in itself looking to identify some physical abnormality to assist in making a complete diagnosis.
But, as others are saying a BG of 4.4 for a non-diabetic is normal and even if you were diabetic, but on no medication, this also would be normal. Even on medication that can not possibly put you into a hypoglcaemic state, such as Metformin, there is still zero risk of hypoglycemia. I think the radiology team that sent you away are blatantly wrong to do that - which is very disappointing for you and others in your position.
I would report this to probably 3 different places - to ensure corrective training is given to whoever made this poor decision and consequently is wasting NHS resources as well as defeating getting you a prompt diagnosis:
1. The booking system that sent you the paperwork that called you in. They will know who set up your requirement for a CT PET scan. They won't know why but can provide simple feedback to the requesting Dep't.
2. The GP or Consultant who you last saw or spoke to that wants the scan result and initiated the scan requirement.
3. The Radiology Department - not only to point out that 4.4 is fine and in accord with the call in instructions but also to point out that sending you home without any advice on what else you might do to raise your BG is unhelpful, wasteful and frankly unprofessional.
I see this as a modest nail that needs firmly hammering home to prevent it from recurring.