The full name is “diabetes mellitus”. Diabetes is when blood sugar rises above 20mM, the kidneys can't hold it all in and so the glucose starts leaking into the urine. This is bad because once it causes an increase in urine glucose levels, it creates an osmotic imbalance. So, extra water begins to flow from the blood into the urine to compensate, which is why the volume of urine is excessive. As a result, the water level in the blood decreases, which stimulates the need to replace water, hence thirst. Excessive thirst (polydipsia) is a consequence. Which is also another symptom of