Can u say "no" if u don't want to have blood taken in the hospital? Even if you are under 18?

Sure why not.

Patients can refuse procedures most times as long as legal matters aren't involved and a judge has ordered blood to be drawn or if the patient has been deemed incompetent to make their own healthcare decisions but refusing can sometimes result in other issues such as not figuring out the cause of your illness and correcting the problem or sometimes insurance coverage can be dropped completely and you would have to pay out of pocket if other issues were to arise due to your refusal.

Blood work is a vital part of protocol. If your an inpatient and they release you while your under certain ailment they can be sued if something goes wrong. Blood lab results detect sicknesses blind to the naked eye.

Yes you can say no ,but , sometimes they need a blood sample to identify an illness .