Hi Dowris
I'm not an expert but have been led to understand that anything over 20, you should go to A/E. However, on reading the posts here recently (I've only started out on this stuff, I have to say) it seems folks can experience higher.
Hopefully, someone with more knowledge about it will post for you soon but, if you don't hear something soon, it might be worth phoning the on-call GP and asking his advise.
If you're ill that can cause a spike whilst your body tries to fight off the infection. I'd keep testing to see if there's any decrease but check with the doctor or NHS Direct as you may need something to treat whatever is making you ill.
I was over 20 at diagnosis, and for the first week or so after. I didn't need to go into A&E but did feel pretty rough.