What serum ketone level is diagnostic for diabetic ketoacidosis (DKA)?

Serum Ketone Levels for Diagnosing DKA

A serum β-hydroxybutyrate (bOHB) level ≥3.0 mmol/L in the presence of hyperglycemia and acidosis is diagnostic for diabetic ketoacidosis (DKA). 1, 2

Diagnostic Criteria for DKA

DKA is characterized by the triad of:

1. Hyperglycemia (blood glucose >250 mg/dL)
2. Metabolic acidosis (pH <7.3, bicarbonate <18 mEq/L)
3. Ketonemia (elevated serum ketones)

Preferred Ketone Measurement

• β-hydroxybutyrate (bOHB) is the predominant ketone body in DKA and the preferred measurement for diagnosis 1
• Normal serum ketone levels are very low (<0.5 mmol/L) 3
• Diagnostic threshold for DKA:
  • Children: bOHB ≥3.0 mmol/L 2
  • Adults: bOHB ≥3.8 mmol/L 2

Why bOHB Measurement is Superior

• bOHB accounts for 75% of ketones in DKA
• The nitroprusside method (used in urine ketone testing) only measures acetoacetic acid and acetone, not bOHB 3
• During DKA treatment, bOHB converts to acetoacetic acid, which can falsely suggest worsening ketosis if using nitroprusside methods 3
• Direct bOHB measurement shows excellent correlation with anion gap (r=0.66) and bicarbonate levels (r=-0.69) 4

Point-of-Care Testing

Point-of-care testing for bOHB offers several advantages:

• Immediate results at triage
• High sensitivity (98%) and specificity (85%) at a cutoff of 1.5 mmol/L 4
• Strong correlation with laboratory measurements (r=0.99) 5

Diagnostic Algorithm

1. Initial assessment: Check capillary blood glucose

   • If >250 mg/dL, proceed to ketone testing

2. Ketone measurement: Measure serum bOHB

   • bOHB ≥3.0 mmol/L (children) or ≥3.8 mmol/L (adults): Highly suggestive of DKA

3. Confirm acidosis: Check venous pH and bicarbonate

   • pH <7.3 and bicarbonate <18 mEq/L: Confirms DKA

4. Additional testing: Complete blood count, electrolytes, renal function, anion gap calculation

Common Pitfalls to Avoid

• Don't rely solely on urine ketones: While sensitive for detecting ketosis, urine ketones are not specific for DKA and don't measure bOHB 3, 1
• Don't use nitroprusside method to monitor treatment: This can mislead clinicians as bOHB converts to acetoacetate during treatment 3
• Don't diagnose DKA based on hyperglycemia alone: Some patients may have euglycemic DKA, especially those on SGLT2 inhibitors
• Don't ignore the need for acidosis: Ketosis without acidosis is not DKA

Monitoring During Treatment

• Monitor serum bOHB levels to track resolution of ketosis
• DKA is considered resolved when:
  • Blood glucose <200 mg/dL
  • Serum bicarbonate ≥18 mEq/L
  • Venous pH >7.3
  • Normalized anion gap 1

Remember that ketonemia typically takes longer to clear than hyperglycemia, so continued monitoring of ketone levels is essential even after blood glucose normalizes 3, 1.