What labs should be ordered for a patient presenting with Diabetic Ketoacidosis (DKA)?

Essential Laboratory Tests for Diabetic Ketoacidosis (DKA)

For patients presenting with suspected DKA, the initial laboratory evaluation should include plasma glucose, blood urea nitrogen/creatinine, serum ketones, electrolytes with calculated anion gap, osmolality, urinalysis, urine ketones by dipstick, arterial blood gases, complete blood count with differential, and electrocardiogram. 1, 2

Core Laboratory Tests for DKA Diagnosis

Immediate Tests (STAT)

• Blood glucose - Typically >250 mg/dL, though euglycemic DKA is possible 3, 4
• Arterial blood gases - To assess pH (<7.3 in DKA) and acid-base status
• Serum electrolytes - Including sodium, potassium, chloride, bicarbonate
• Calculated anion gap - Formula: [Na⁺] - ([Cl⁻] + [HCO₃⁻]), typically >10-12 mEq/L in DKA
• Serum ketones - Direct measurement of β-hydroxybutyrate preferred over nitroprusside method
• BUN/creatinine - To assess renal function and dehydration status
• Urinalysis - For glucose and ketones
• Calculated serum osmolality - Formula: 2[measured Na (mEq/L)] + glucose (mg/dL)/18

Additional Essential Tests

• Complete blood count with differential - To assess for infection and dehydration
• Electrocardiogram - To evaluate cardiac status and effects of electrolyte abnormalities 5
• HbA1c - To differentiate between new-onset diabetes and poor control of known diabetes 1

Tests to Identify Precipitating Factors

• Bacterial cultures (urine, blood, throat) - If infection is suspected 1
• Chest X-ray - If respiratory symptoms are present or infection is suspected
• Additional tests based on clinical presentation:
  • Amylase/lipase - If pancreatitis is suspected
  • Cardiac enzymes - If myocardial infarction is suspected
  • Toxicology screen - If drug abuse is suspected

Monitoring Tests During Treatment

• Blood glucose - Every 1-2 hours 2
• Electrolytes, BUN, creatinine - Every 2-4 hours 2
• Venous pH or arterial blood gases - To monitor resolution of acidosis
• Serum potassium - Critical to monitor before and during insulin therapy 6

Interpretation and Clinical Correlation

Diagnostic Criteria for DKA 1

• Plasma glucose >250 mg/dL (though can be lower in euglycemic DKA)
• Arterial pH <7.3
• Serum bicarbonate <18 mEq/L
• Positive serum ketones
• Anion gap >10-12 mEq/L

Common Pitfalls to Avoid

1. Failing to check potassium before starting insulin - 5.6% of DKA patients present with hypokalemia, which can worsen with insulin therapy 6
2. Relying solely on nitroprusside method for ketone measurement - This only measures acetoacetic acid and acetone, not β-hydroxybutyrate (the predominant ketone in DKA) 1
3. Missing euglycemic DKA - Some patients may present with blood glucose <250 mg/dL, particularly those on SGLT2 inhibitors 4
4. Overlooking cardiac complications - Electrolyte abnormalities in DKA can cause ECG changes and arrhythmias 5

Algorithm for Laboratory Assessment in Suspected DKA

1. Initial laboratory panel (STAT): Blood glucose, arterial blood gases, electrolytes, BUN/creatinine, serum ketones, CBC, urinalysis
2. Calculate: Anion gap, corrected sodium, serum osmolality
3. Obtain ECG to assess for cardiac effects of electrolyte abnormalities
4. Order additional tests based on suspected precipitating factors
5. Monitor key parameters during treatment: glucose, electrolytes, acid-base status

By systematically ordering and interpreting these laboratory tests, clinicians can promptly diagnose DKA, identify precipitating factors, guide treatment, and monitor response to therapy, ultimately improving patient outcomes.