8 year old always thirsty

[tejodouro]

My daughter is 8 years old.  She is always very thirsty and uses the bathroom alot, including once or twice per night.  She has average behavior for her age but her behavior is not good right after she eats a meal, most of all breakfast.  She becomes loud and hyper.  I requested about a year ago a diabetes test from her doctor.  He did a urine test at the office and told me that it was negative.  My questions for you moms that are experts with diabetes:
(1) Is the office urine test always reliable?
(2) Could she have diabetes.  I am surprised how much water she drinks all day long.  She even drinks water during the night. I have another daughter and she does not drink 1 tenth of the water that her sister does.
(3) Is there another test that I should request from her doctor? what is the best test for childhood diabetes?
Thank you,

[Zoelula]

Yes, I certainly would want to explore the possibility of diabetes a bit more. I don't know what the urine test was (protein in her urine?) but the standard for diabetes is a fasting blood test called an A1C which shows blood sugar averages for a period of a couple months and/or an OGTT which would give her a very sweet drink and then test its influence on her blood sugar over a couple hours. I would press the doctor to do these tests and if not see a different doctor. It could be nothing, but that would be good to know as well.