No one wants to have high blood sugar—you'd rather feel your best. But there's even more to it. When your blood sugar is high, your body can't move the large amount of glucose in the blood into your cells. Instead, your body uses more fat for fuel. And when fat is burned in this way, ketones are formed.
Any time your blood sugar is over 240, you should immediately use a ketone test strip to check your urine.1
Ketones make the blood acidic, making you feel ill and possibly leading to diabetic ketoacidosis (or DKA). DKA is a serious medical condition that causes nausea and vomiting. With vomiting can come severe dehydration as well. When a person has DKA, immediate hospitalization may be necessary, as untreated DKA can be deadly.
If you wear an insulin pump, you have to take note any time there is a disruption in insulin delivery—if the site falls out or is disconnected, if the cannula is bent, or if insulin is not being absorbed properly. Because your insulin pump uses short-acting insulin, blood sugar can increase in just a few hours and ketones can form.