What Ketones in Urine Mean
Ketones in urine indicate your body is breaking down fat for energy instead of using glucose, which can be normal (fasting, pregnancy) or pathological (diabetic ketoacidosis in people with diabetes). 1
Normal Physiological Causes
Ketone bodies are normally present in blood and urine but usually below detection limits of routine testing methods. 1
Up to 30% of first morning urine specimens from pregnant women show positive ketones as a normal finding due to physiologic starvation ketosis from nausea/vomiting or fasting. 2
Positive ketone readings occur in normal individuals during fasting and prolonged exercise as the body shifts to fat metabolism when glucose is not readily available. 3, 4
Pathological Causes in Diabetes
In diabetic patients, especially those with type 1 diabetes, elevated ketones suggest insufficient insulin and may indicate impending or established diabetic ketoacidosis (DKA), which is a medical emergency. 3
The presence of urine ketones is highly sensitive for DKA with high negative predictive value, making it useful for ruling out DKA. 1
Prolonged hyperglycemia in type 1 diabetes can result in DKA, with first symptoms including drowsy feeling, flushed face, thirst, loss of appetite, and fruity odor on breath, followed by heavy breathing and rapid pulse. 5
Critical Limitations of Urine Ketone Testing
Urine ketone tests using nitroprusside-containing reagents only detect acetoacetate and NOT β-hydroxybutyrate, which is the predominant ketone body in DKA (up to 10:1 ratio). 1, 3
This causes significant underestimation of total ketone body concentration and can provide misleading clinical information. 1
As DKA resolves, β-hydroxybutyrate is oxidized to acetoacetate, so urine ketone tests might be increasing even as DKA is resolving due to this lag. 4
False-positive results occur with highly colored urine and sulfhydryl drugs including captopril, while false-negative readings occur when test strips are exposed to air or urine specimens are highly acidic. 3
When to Act Immediately (Red Flags)
For people with diabetes, seek emergency medical attention if ketones are present along with:
- Blood glucose that does not improve with insulin administration 6
- Inability to tolerate oral hydration due to vomiting 6
- Altered mental status 6
- Ketone levels that continue to increase despite interventions 6
- Symptoms of DKA: abdominal pain, nausea, vomiting, drowsiness, fruity breath odor 2, 5
Management Algorithm for Diabetic Patients
For mild ketosis (1+ ketones) with diabetes:
- Increase oral fluid intake immediately to prevent dehydration 6
- Monitor blood glucose and ketone levels every 3-4 hours 1, 6
- Administer additional short or rapid-acting insulin if blood glucose is elevated 1, 6
- For normal blood glucose but elevated ketones, consume carbohydrates along with insulin to help suppress ketone production 3
Special High-Risk Populations
Individuals treated with SGLT2 inhibitors are at increased risk for euglycemic DKA (DKA with relatively normal blood glucose levels). 6, 4
Pregnant individuals may present with euglycemic DKA and should seek immediate medical attention if ketones are elevated, as this represents a life-threatening emergency. 2, 6
Metformin is contraindicated in diabetic ketoacidosis and should not be used for treatment. 7
Preferred Testing Method
Blood ketone testing measuring β-hydroxybutyrate is strongly preferred over urine ketone testing for diagnosing and monitoring DKA, as it directly measures the predominant ketone body. 1, 3
Children with type 1 diabetes randomized to blood ketone testing had almost half the number of emergency department visits or hospitalizations compared to urine ketone testing. 1
Blood β-hydroxybutyrate normalization occurs faster than urine ketone clearance (17.4 vs 19.7 hours), making it a better indicator of metabolic control. 8