Foundations, Part 10
Ketones in Type 1 Diabetes
Sometimes glucose is the loudest signal that something is wrong, and sometimes it is the quietest. This page is about what ketones are, what the levels mean, when to test, and the one situation in type 1 diabetes where ketones can be climbing while glucose still looks fine.
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What ketones are
Picture insulin as the doorkey for cells: glucose can knock all it likes, but without insulin the door stays shut. When insulin is absent or insufficient in type 1 diabetes, cells starve in the middle of plenty, and the body switches to breaking down stored fat for energy instead.
That fat breakdown produces three molecules collectively known as ketone bodies:
- Beta-hydroxybutyrate (BHB), the most abundant, and the one measured by blood ketone meters
- Acetoacetate, measured by urine ketone strips
- Acetone, a volatile by-product that produces the characteristic “fruity breath” sometimes noticed during high ketone states
Small amounts of ketones are entirely normal: the body produces them during overnight fasting, prolonged exercise, and low-carbohydrate eating, and uses them efficiently as an alternative fuel. The problem arises when ketone production accelerates beyond the body’s ability to use them, accumulating in the blood and making it progressively more acidic, a state that, if unchecked, leads to diabetic ketoacidosis (DKA).
Why ketones matter uniquely in type 1 diabetes
People with type 1 diabetes are uniquely vulnerable to dangerous ketone accumulation because they cannot produce their own insulin. Without insulin, two things happen at once: glucose cannot enter cells, so cells are starved of fuel even while blood glucose climbs; and the liver accelerates both glucose output and ketone production, because insulin normally suppresses both processes, and without it, both run unchecked.
This creates a vicious cycle: rising glucose, rising ketones, increasing acidity. In someone who produces their own insulin (type 2 diabetes, for example), even a small amount of residual insulin production acts as a brake on this cycle. In type 1 diabetes, that brake is absent.
This is the mechanism behind DKA. It is not simply “high glucose”; it is the combination of insulin absence, unrestrained ketone production, and the resulting acidosis that makes DKA dangerous.
Types of ketone tests
Two ways to test, two different molecules. Blood meters measure beta-hydroxybutyrate directly, the predominant ketone body during insulin deficiency, giving a real-time picture of what is happening now. Urine strips measure acetoacetate, which reflects what was happening hours ago when the urine was produced; they can also show positive during recovery (when ketones are actually falling), because the body converts BHB back to acetoacetate as it clears.
Blood testing is the preferred method for type 1 diabetes. Many diabetes teams recommend keeping a blood ketone meter and test strips at home at all times. Urine strips are better than nothing, but blood testing gives a more accurate and timely result.
Understanding ketone levels
Blood ketone levels (beta-hydroxybutyrate, measured in mmol/L) are generally interpreted in four ranges. These are averages and general guidance; individual circumstances and clinical advice from a diabetes team always take precedence.
| Level (mmol/L) | Category | What this typically means |
|---|---|---|
| Below 0.6 | Normal | No concern. Within the range seen during normal fasting or after exercise. |
| 0.6 to 1.4 | Mildly elevated | Needs attention. Common causes include missed insulin, infusion site failure, illness, or prolonged fasting. Many people find it helpful to check insulin delivery is intact, apply a correction, hydrate, and retest in around two hours. |
| 1.5 to 2.9 | Significantly elevated | Indicates a substantial insulin deficit. The typical approach involves a pen correction (often around 20 per cent of total daily dose), changing the infusion site, suspending AID if applicable, hydrating aggressively, and retesting in one hour. Many diabetes teams advise making contact if levels are not falling after two hours. |
| 3.0 or above | High, urgent | DKA risk is high at this level. This generally warrants urgent medical attention, emergency department or immediate contact with the diabetes team. |
The specific protocol agreed with a diabetes care team always takes priority over general guidance.
Euglycaemic DKA, when glucose is not the whole story
One of the most important things to understand about ketones is that they can be dangerously elevated even when glucose is not particularly high. This is known as euglycaemic DKA, and it catches people off guard because the usual warning sign, persistent high glucose, may be absent or only mildly elevated.
Situations where euglycaemic DKA is more commonly seen include SGLT-2 inhibitor use (these medications lower glucose by causing it to be excreted in urine, masking the glucose rise that would normally accompany insulin deficiency); prolonged fasting or very low carbohydrate intake; illness with vomiting, where reduced food intake plus stress hormones drive ketone production without the expected glucose spike; and after heavy or prolonged exercise, where glycogen depletion and increased fat metabolism can drive ketones while glucose remains in range.
The key message: when feeling unwell, check ketones, not just glucose. Glucose alone does not tell the full story.
Ketones after hypoglycaemia
Some people notice elevated ketone readings after a severe hypo. The mechanism: during a significant hypoglycaemic episode, the counter-regulatory hormone surge (cortisol, glucagon, adrenaline) mobilises stored fat, and ketone bodies are produced as a by-product. Once glucose is restored, those ketones can still appear elevated for a few hours before falling back to normal. Worth knowing because the reading can look alarming but does not require the same response as ketones caused by insulin deficiency. Context matters.
When to test ketones
Many diabetes teams suggest testing blood ketones in the situations below. Tap each for the detail.
During illness
Especially with fever, vomiting, or reduced food intake. Counter-regulatory hormones during infection drive both glucose and ketones up, and reduced eating does not protect against this.
Persistent glucose above 14 mmol/L for 90 minutes or more
Particularly if corrections are not bringing it down. This is the early-warning pattern that ketone production may have started; the Hyperglycaemia page covers the action framework.
Nausea or vomiting
These can be both a cause and a symptom of rising ketones. Worth a check even when glucose looks fine.
After a severe hypo
To check for transient counter-regulatory ketone elevation (see the section above). Usually transient and not dangerous, but worth the reassurance.
Pump or infusion site problems
A site failure means no insulin delivery, and ketones can rise quickly, sometimes within hours. Test ketones any time a site change is being made because of unexplained highs.
Feeling generally unwell with no clear explanation
Sometimes the first sign of a problem is a vague sense of being “off”. A ketone test takes thirty seconds and rules out one of the more serious possibilities.
For the step-by-step action protocol when ketones are elevated, see the Hyper Treatment Explorer in the GNL app, which surfaces a population-average ketone correction estimate at your total daily insulin and routes paediatric high-ketones via ISPAD Chapter 13 sick-day rather than adult DAFNE or BERTIE pathways.
This content is for educational exploration only. It describes average responses and general principles. It is not medical advice and cannot replace individual clinical guidance from your diabetes care team.
Part 10 of 12
Ketones in Type 1 Diabetes