Ketonuria in a 12-Year-Old with Normal Glucose: Clinical Approach
In a 12-year-old girl with ketonuria and a normal random blood glucose of 91 mg/dL, without vomiting, diarrhea, or weight loss, this most likely represents benign physiologic ketosis from fasting or inadequate caloric intake rather than diabetic ketoacidosis, and does not require insulin therapy.
Immediate Assessment
Rule Out Diabetic Ketoacidosis First
The normal blood glucose of 91 mg/dL makes diabetic ketoacidosis (DKA) highly unlikely, as DKA traditionally requires hyperglycemia >250 mg/dL along with metabolic acidosis and ketonemia 1, 2, 3. However, you must remain vigilant because:
- Euglycemic DKA can occur at lower glucose levels, particularly in patients taking SGLT2 inhibitors or during pregnancy, though this is uncommon in a 12-year-old 3
- The absence of classic DKA symptoms (vomiting, abdominal pain, weight loss) strongly argues against DKA 2, 3
Obtain Critical Additional Information
Ask about recent dietary intake and fasting duration, as ketones are normally present during fasting and can be detected in up to 30% of first morning urine specimens in healthy individuals 1, 4. Specifically inquire about:
- Time of last meal and adequacy of recent caloric intake 4, 5
- Any intentional dieting or calorie restriction 5
- Timing of urine collection (first morning specimens commonly show physiologic ketonuria) 1
Diagnostic Workup
Essential Laboratory Tests
Measure fasting plasma glucose and HbA1c to screen for undiagnosed diabetes, as approximately one-third of DKA cases occur in persons without known diabetes 1, 2. The diagnostic thresholds are:
- Fasting plasma glucose ≥126 mg/dL indicates diabetes 1
- HbA1c ≥6.5% indicates diabetes 1
- Random glucose ≥200 mg/dL with symptoms indicates diabetes 1
If diabetes screening is positive or clinical suspicion remains high, obtain venous pH and serum bicarbonate, as DKA requires pH <7.3 and bicarbonate <18 mEq/L 1, 6, 2, 3.
Preferred Ketone Testing Method
Blood β-hydroxybutyrate measurement is superior to urine ketone testing for diagnosing and monitoring ketoacidosis, as it measures the predominant ketone body directly 1, 4, 6. Important limitations of urine testing include:
- Urine dipsticks only detect acetoacetate, missing β-hydroxybutyrate 1, 6
- False-positives occur with sulfhydryl drugs (e.g., captopril) and highly colored urine 1, 4
- False-negatives occur with expired test strips or highly acidic urine 1, 4
Most Likely Diagnosis: Starvation Ketosis
Given the normal glucose and absence of symptoms, this represents physiologic starvation ketosis, which is a benign adaptive response to inadequate carbohydrate or caloric intake 4, 5. Key distinguishing features:
- Starvation ketosis occurs with normal glucose control but insufficient intake 4, 5
- It does not cause metabolic acidosis or require insulin therapy 4, 5
- Management consists of increasing dietary carbohydrate and caloric intake 4, 5
Management Algorithm
For Confirmed Starvation Ketosis (Normal Glucose, No Symptoms)
Increase oral carbohydrate intake and ensure adequate total calories, particularly if the patient has been fasting, dieting, or has inadequate nutritional intake 4, 5. Specific recommendations:
- Provide carbohydrate-rich foods or beverages immediately 5
- Ensure minimum carbohydrate intake of at least 150 g per day 5
- Avoid further calorie restriction 5
Do not initiate insulin therapy when glucose is normal and ketonuria is isolated, as the issue is nutritional rather than insulin-related 5.
If Diabetes Is Newly Diagnosed
When diabetes is confirmed but the patient is metabolically stable (no ketoacidosis), initiate metformin as first-line therapy if the patient meets criteria 1:
- Metabolically stable means A1C <8.5% and asymptomatic 1
- Random glucose <250 mg/dL without ketoacidosis 1
- Metformin is preferred over insulin in this scenario 1
If ketosis or ketoacidosis is present at diabetes diagnosis, insulin therapy is mandatory until fasting and postprandial glycemia normalize, after which metformin can be added 1.
Critical Pitfalls to Avoid
Do not assume all ketonuria represents DKA—ketones are commonly present during normal fasting 1, 4.
Do not rely solely on urine ketone testing to diagnose or monitor DKA, as it is unreliable and can mislead clinical decision-making 1, 4, 6.
Do not start insulin if glucose is normal and the patient is asymptomatic, as this represents starvation ketosis requiring nutritional intervention 4, 5.
Do not ignore persistent or worsening ketonuria—if symptoms develop (nausea, vomiting, abdominal pain, mental status changes) or glucose rises, immediate medical evaluation is required 4, 6.
When to Escalate Care
Seek immediate medical evaluation if any of the following develop 4, 6: