The difference between diabetes mellitus and diabetes insipidus is that

• In diabetes mellitus:

Ketone bodies can be present in the urine due to the body's inability to properly use glucose for energy. When there's a lack of insulin (as in type 1 diabetes) or insulin resistance (as in type 2 diabetes), the body breaks down fats for energy, leading to the production of ketone bodies as byproducts. This can result in a condition known as diabetic ketoacidosis (DKA), characterized by high blood sugar levels, high ketone levels, and acidic blood pH.

• In diabetes insipidus:

Ketone bodies are typically not present in the urine because diabetes insipidus is unrelated to glucose metabolism. Diabetes insipidus is a disorder of water balance and urine concentration caused by insufficient production or action of antidiuretic hormone (ADH), also known as vasopressin. It leads to excessive thirst and urination of dilute urine. Unlike in diabetes mellitus, the absence of ADH doesn't directly influence glucose metabolism or ketone production.