Why is ketonuria 3+ present despite normal blood glucose levels?

Ketones (+++) with normal blood glucose levels typically occur when the body has been in a prolonged fasting state or after intense physical exercise, as detailed below:

First, prolonged fasting: Healthy individuals may be unable to eat due to conditions such as fever or severe vomiting, resulting in extended fasting. During fasting, the body breaks down fat for energy; this process generates ketone bodies, which are excreted in large amounts in the urine. Urinalysis thus reveals ketonuria (3+). Since these individuals do not have diabetes and their carbohydrate metabolism remains normal, blood glucose levels remain within the normal range.

Second, intense exercise: Vigorous physical activity increases fat utilization. As fatty acids undergo oxidative metabolism, ketone bodies appear in the urine.

Ketone bodies—comprising acetoacetate, β-hydroxybutyrate, and acetone—are intermediate products of hepatic fatty acid oxidation. They are not generated as a result of hyperglycemia, nor does dietary carbohydrate intake increase ketone production. Thus, elevated ketone levels can occur independently of high blood glucose.

Therefore, in daily life, it is important to avoid excessive stress and fatigue, consume adequate staple foods, and prevent fasting-induced metabolic stress. If symptoms such as high fever, severe vomiting, or diarrhea occur, prompt medical attention is essential, and intravenous energy supplementation may be required to prevent ketosis.