Can i drink tea or coffee while fasting for bloods for thyroid etc?

Try Not: Fasting for thyroid tests not usually needed so perhaps you are also having lipids, cortisol or blood glucose as well. Best if only water for the 12 hours prior to fasting tests. Some evidence that perhaps caffeine can impact blood sugar very slightly (though may be insignificant). Some sources of coffee (eg via percolator) have oils that raise triglyceride levels. Wait for that cup if you can.