Ketones
Fuel your body makes from fat when glucose is scarce; high levels can be dangerous.
When cells can't get enough glucose, the liver breaks down fat into ketones as an alternative fuel. Light ketosis happens with fasting or low-carb eating and is usually harmless.
But in diabetes, very high glucose plus rising ketones can signal diabetic ketoacidosis (DKA), a medical emergency. If you're advised to check for ketones when glucose runs high, follow that guidance promptly.