Hi Saffrons
Normally the only problem we sometimes get with bloods is low haemoglobin (anaemia) which if its a first occurance would have to be investigated, if its chronic long standing we normally contact GP for treatment if not already on iron.
The other is low potassium, and although its usually when you are on pre op diet - hence the recommended fruits (orange/banana etc) it can also happen if you take diuretics particularly furosimide or bendroflumethiazide, if its down on preassessment bloods you will get a phonecall from staff to advise on how to correct it.
Good luck with op