How to diagnose diabetic ketoacidosis in urgent care?

How to Diagnose Diabetic Ketoacidosis in Urgent Care

Diagnose DKA immediately using three simultaneous criteria: blood glucose >250 mg/dL, venous pH <7.3, and serum bicarbonate <15 mEq/L, with elevated blood ketones (preferably β-hydroxybutyrate). 1

Initial Diagnostic Workup

Obtain the following tests STAT when DKA is suspected:

• Blood glucose to confirm hyperglycemia >250 mg/dL (though be aware euglycemic DKA can occur, particularly with SGLT2 inhibitors) 1, 2
• Venous blood gas for pH and bicarbonate measurement—this is sufficient and avoids unnecessary arterial sticks 3, 1
• Complete metabolic panel including sodium, potassium, chloride, bicarbonate, BUN, and creatinine 1, 4
• Blood β-hydroxybutyrate (the gold standard ketone measurement, NOT urine ketones) 1, 5
• Complete blood count with differential to identify infection or other precipitating factors 3, 4
• Urinalysis with dipstick 3, 4
• Electrocardiogram to detect cardiac complications and monitor for potassium-related arrhythmias 3, 4
• Serum osmolality to assess hyperosmolar state 3, 4

Core Diagnostic Criteria

All three components must be present simultaneously for DKA diagnosis 1:

1. Hyperglycemia: Blood glucose >250 mg/dL 3, 1
2. Metabolic acidosis: Venous pH <7.3 3, 1
3. Low bicarbonate: Serum bicarbonate <15 mEq/L 3, 1
4. Elevated ketones: Moderate ketonuria or ketonemia (preferably β-hydroxybutyrate) 3, 1

Calculate the anion gap using [Na⁺] - ([Cl⁻] + [HCO₃⁻]), which should be >10-12 mEq/L in DKA 1, 4. This confirms high anion gap metabolic acidosis and helps distinguish DKA from other causes of acidosis.

Severity Classification

Classify DKA severity immediately as it determines monitoring intensity and prognosis 1:

• Mild DKA: pH 7.25-7.30, bicarbonate 15-18 mEq/L, anion gap >10, alert mental status 1, 4
• Moderate DKA: pH 7.00-7.24, bicarbonate 10-15 mEq/L, anion gap >12, drowsy/lethargic 1, 4
• Severe DKA: pH <7.00, bicarbonate <10 mEq/L, anion gap >12, stuporous or comatose—requires intensive monitoring and has higher mortality 1, 6

Clinical Presentation to Look For

The classical presentation includes 1:

• History: Polyuria, polydipsia, weight loss, vomiting, abdominal pain, weakness, altered mental status
• Physical findings: Poor skin turgor, Kussmaul respirations (deep, rapid breathing), tachycardia, hypotension, fruity breath odor, altered mental status
• Additional signs: Up to 25% may have coffee-ground emesis due to hemorrhagic gastritis 1

Critical Pitfall: β-Hydroxybutyrate vs. Urine Ketones

Never rely on urine ketones or nitroprusside-based tests for diagnosis or monitoring. 1, 6 These methods only measure acetoacetate and acetone, completely missing β-hydroxybutyrate—the predominant and strongest ketoacid in DKA. During treatment, β-hydroxybutyrate converts to acetoacetate, which paradoxically makes nitroprusside tests appear worse even as the patient improves. 1, 6

Point-of-care β-hydroxybutyrate testing (e.g., Precision Xtra meter) has 98% sensitivity and 85% specificity at the threshold of 1.5 mmol/L, making it highly accurate for immediate diagnosis at triage. 5

Differential Diagnosis

Distinguish DKA from other causes of high anion gap metabolic acidosis 3, 1:

• Starvation ketosis: Glucose rarely >250 mg/dL, bicarbonate usually not <18 mEq/L 3
• Alcoholic ketoacidosis: Glucose ranges from mildly elevated to hypoglycemia, distinguished by clinical history 3
• Lactic acidosis: Measure blood lactate 1
• Toxic ingestions: Salicylate, methanol, ethylene glycol—identified by specific tests and clinical presentation 3, 1
• Chronic renal failure: Typically causes hyperchloremic acidosis rather than high anion gap 3

Additional Calculations

Correct serum sodium for hyperglycemia: Add 1.6 mEq/L for every 100 mg/dL glucose above 100 mg/dL. 3, 4 This corrected sodium guides subsequent fluid choice during treatment.

When to Obtain Cultures

Obtain bacterial cultures of urine, blood, and throat if infection is suspected, as infection is a common precipitating factor. 6 Also obtain chest X-ray if clinically indicated. 3

Special Consideration: Euglycemic DKA

Be aware that patients on SGLT2 inhibitors can develop euglycemic DKA with relatively normal glucose levels (<250 mg/dL) but still meet the other criteria for DKA (acidosis, ketosis). 1, 2 This is an increasingly recognized phenomenon that can cause diagnostic confusion if you rely solely on glucose levels.

Monitoring Strategy

After initial diagnosis, venous pH and anion gap adequately monitor acidosis resolution without requiring repeated arterial blood gases. 3, 1 Venous pH is typically 0.03 units lower than arterial pH. 6