Final answer:
Ketonuria is the pathological presence of ketones in the urine, often associated with diabetes mellitus or other conditions where the body utilizes fat instead of glucose for energy.
Step-by-step explanation:
The pathological presence of ketones in the urine is called ketonuria. Ketones are byproducts of fat metabolism, and their presence in the urine suggests that the body is using fat for energy instead of glucose, which can occur in conditions such as diabetes mellitus. In diabetes, either due to insufficient insulin or insulin resistance, glucose cannot be taken up by the cells and remains in the bloodstream. As a result, the body turns to fat as an energy source, leading to the production of excess ketones. These are then excreted in the urine, causing ketonuria. Ketonuria can also be indicative of other conditions, such as severe protein or carbohydrate deficiency in the diet or during states of starvation, fever, and frequent pregnancies.