Diabetes Insipidus and Osmolality levels

Patient: HiMy 3 year old son drinks on average about 3 litres of fluid a day, and has excessive urination. He also wakes every night, several times for water.My doctor has tested him for Diabetes Insipidus, and his urine osmolality has come back as 814 after 12 hours without fluids.My doctor said that anything above 700 rules out DI, but I wanted to check that this was the case even after fluid restriction?Thanks

Symptoms: Extreme thirst
excessive urination
tiredness & irritability
complains of sore back
No ketones in urine though (Type 2 diabetes has been ruled out)