Diagnostic Criteria for Diabetic Ketoacidosis (DKA)
DKA is diagnosed when all three of the following criteria are met: blood glucose ≥250 mg/dL, arterial pH <7.3, and serum bicarbonate <15 mEq/L, along with positive serum or urine ketones. 1
Core Diagnostic Triad
The American Diabetes Association guidelines establish a severity-stratified approach to DKA diagnosis based on three biochemical parameters 1:
Mandatory Criteria (All Must Be Present):
- Plasma glucose: ≥250 mg/dL
- Arterial pH: <7.3 (with severity gradations: mild 7.25-7.30, moderate 7.00-7.24, severe <7.00)
- Serum bicarbonate: <15 mEq/L (mild 15-18 mEq/L, moderate 10-15 mEq/L, severe <10 mEq/L)
- Ketones: Positive serum or urine ketones (by nitroprusside method)
- Anion gap: ≥10 mEq/L (calculated as Na - [Cl + HCO3])
Important Clinical Nuances
The Hyperglycemia Threshold Is Being De-emphasized
Recent evidence shows that hyperglycemia should no longer be considered an absolute requirement for DKA diagnosis 2. This shift recognizes the increasing incidence of euglycemic DKA, particularly in patients taking SGLT-2 inhibitors, where blood glucose may be <250 mg/dL despite meeting all other criteria for ketoacidosis 2, 3.
Venous vs. Arterial Blood
Use venous pH rather than arterial blood gases unless respiratory compromise is present 1, 4. Venous pH is typically ~0.03 units lower than arterial pH and is sufficient for diagnosis and monitoring. This reduces patient discomfort and is equally reliable for DKA management 1.
Essential Laboratory Workup
Beyond the diagnostic triad, obtain 1:
- Electrolytes with calculated anion gap
- Blood urea nitrogen and creatinine (assess renal function and dehydration)
- Complete blood count with differential (evaluate for infection/leukocytosis)
- Urinalysis with urine ketones
- Electrocardiogram (assess for hyperkalemia changes and cardiac precipitants)
- Serum osmolality: Calculate as 2[Na] + glucose/18 (typically variable in DKA, vs. ≥320 mOsm/kg in HHS)
Critical Pitfalls to Avoid
Ketone Measurement Method Matters
The nitroprusside method (standard urine/serum ketone testing) only measures acetoacetate and acetone, NOT β-hydroxybutyrate (β-OHB), which is the predominant ketoacid in DKA 1. During treatment, β-OHB converts to acetoacetate, which can falsely suggest worsening ketosis when the patient is actually improving. Blood β-OHB measurement is the preferred monitoring method 1, 4.
Corrected Sodium Is Essential
Always correct serum sodium for hyperglycemia: add 1.6 mEq/L to the measured sodium for every 100 mg/dL glucose above 100 mg/dL 1. This prevents misinterpretation of electrolyte status and guides appropriate fluid selection.
Clinical Diagnosis Trumps Laboratory Values
In real-world practice, approximately 31% of patients diagnosed with DKA do not meet strict laboratory criteria at presentation 5. Emergency physicians appropriately use clinical judgment when laboratory values are borderline, recognizing that DKA is ultimately a clinical diagnosis supported by—but not solely defined by—laboratory thresholds 5.
Differential Diagnosis Considerations
Distinguish DKA from 1:
- Starvation ketosis: Glucose rarely >250 mg/dL, bicarbonate usually ≥18 mEq/L
- Alcoholic ketoacidosis: Normal to low glucose (often hypoglycemic), history of alcohol use
- Hyperosmolar hyperglycemic state (HHS): Glucose typically ≥600 mg/dL, pH >7.3, bicarbonate ≥15 mEq/L, minimal ketones, osmolality ≥320 mOsm/kg
Resolution Criteria
DKA is considered resolved when glucose <200 mg/dL, serum bicarbonate ≥18 mEq/L, and venous pH >7.3 1. All three criteria must be met before transitioning from intravenous to subcutaneous insulin.