Ketones are chemicals your body produces when it breaks down fat for energy instead of using glucose. In diabetes, ketones typically appear when your cells can’t get enough glucose, either because there isn’t enough insulin or because insulin isn’t working effectively. A small amount of ketones is normal, but when they build up in your blood, they make it dangerously acidic, a condition called diabetic ketoacidosis (DKA).
Why Diabetes Causes Ketone Buildup
Insulin acts like a key that lets glucose enter your cells. When insulin is missing or severely insufficient, glucose stays trapped in your bloodstream while your cells starve. Your body responds by switching to its backup fuel source: fat. Breaking down fat produces ketones as a byproduct, and in small quantities this is perfectly fine. Your brain and muscles can use ketones for energy.
The problem starts when this process runs unchecked. Without insulin to slow things down, fat breakdown accelerates and ketones flood the bloodstream faster than your body can clear them. Ketones are acidic, so as levels climb, your blood pH drops. Healthy blood pH sits around 7.35 to 7.45. In mild DKA, it falls to 7.25 to 7.3. In severe DKA, it can drop below 7.0, which is life-threatening.
This is most common in type 1 diabetes, where the body produces little or no insulin. But it can also happen in type 2 diabetes during severe illness, infection, or when medications aren’t managing blood sugar well enough. Blood sugar in DKA usually exceeds 250 mg/dL, though DKA can occasionally develop at lower blood sugar levels too.
Common Triggers for Ketones
The most frequent trigger is not getting enough insulin. This can happen if you miss a dose, if your insulin pen or pump malfunctions, or if your insulin has gone bad from heat exposure. Illness is the second major trigger. When your body fights an infection or fever, it releases stress hormones that raise blood sugar and increase insulin resistance. Even a common cold or stomach bug can tip the balance.
Other triggers include surgery, physical trauma, certain medications (particularly steroids), and emotional stress. Dehydration from vomiting or diarrhea makes things worse because your kidneys lose some of their ability to flush excess ketones. This is why “sick day rules” matter so much for people with diabetes: checking blood sugar and ketones more frequently during any illness can catch a dangerous rise before it escalates.
What Ketone Buildup Feels Like
Early signs are easy to dismiss. You might feel unusually thirsty, urinate more often than normal, or notice fatigue that seems out of proportion. Nausea and stomach pain are common, and some people describe a general “off” feeling they can’t quite place.
As ketone levels climb, more distinctive symptoms appear. One of the most recognizable is fruity-smelling breath, caused by acetone. Acetone is one of three types of ketones your body produces during fat breakdown, and it’s volatile enough to escape through your lungs when you exhale. Breathing may become rapid and deep as your body tries to blow off excess acid through carbon dioxide. Confusion, difficulty concentrating, and extreme drowsiness signal that the situation is becoming urgent.
How Ketone Levels Are Tested
There are two ways to check ketones: blood tests and urine tests. Blood testing is more accurate and gives real-time results. It measures a specific ketone called beta-hydroxybutyrate, which is the most abundant ketone during DKA. Urine strips are cheaper and easier to find over the counter, but they reflect ketone levels from a few hours earlier rather than right now.
For blood ketone meters, the ranges break down like this:
- Below 0.6 mmol/L: Normal. No action needed.
- 0.6 to 1.5 mmol/L: Low to moderate DKA risk. Recheck in a couple of hours and make sure you’re getting adequate insulin and fluids.
- 1.6 to 2.9 mmol/L: High DKA risk. Contact your healthcare team promptly.
- 3.0 mmol/L or above: Very high DKA risk. This level correlates with the need for emergency treatment.
If you use an insulin pump or have type 1 diabetes, keeping a blood ketone meter at home is a practical safety net, especially during illness. A simple check can be the difference between catching a problem early and ending up in the emergency room.
When Ketones Become a Medical Emergency
DKA can develop in hours, not days. Mild DKA (pH above 7.25) can often be treated in an emergency department over four to six hours without a full hospital admission. Moderate and severe DKA require longer treatment with IV fluids and insulin, often in an intensive care setting.
Certain signs mean you need immediate help: vomiting that won’t stop (which prevents you from drinking fluids or keeping oral medication down), blood ketones above 3.0 mmol/L, confusion or difficulty staying awake, and rapid labored breathing. A person who is unresponsive to voice commands or has dangerously low blood pressure needs critical care right away. DKA is fatal if untreated, but with prompt treatment, most people recover fully.
Keeping Ketones in Check
For people with type 1 diabetes, consistent insulin delivery is the single most important prevention strategy. That means having backup supplies, checking pump sites regularly for kinks or dislodged needles, and never skipping long-acting insulin doses. For people with type 2 diabetes, staying on top of medication during illness is key, even if you’re not eating much.
During sick days, the CDC recommends checking blood sugar more often than usual, since illness-related hormones can spike glucose unpredictably. Staying hydrated helps your kidneys clear ketones. If you notice ketones creeping above 0.6 mmol/L, extra fluids and a correction dose of rapid-acting insulin (if your care plan includes one) can often bring levels back down before they become dangerous. Having a written sick day plan from your care team, with specific steps for different ketone levels, removes guesswork during the moments when clear thinking matters most.