What arterial blood gas findings are typical in primary adrenal insufficiency (Addison's disease)?

Arterial Blood Gas Findings in Primary Adrenal Insufficiency

Primary adrenal insufficiency typically presents with metabolic acidosis on arterial blood gas analysis, though the specific ABG pattern is not the primary diagnostic feature—electrolyte abnormalities and hormonal testing are far more critical.

Expected ABG Pattern

• Metabolic acidosis is the characteristic acid-base disturbance in primary adrenal insufficiency, reflecting both mineralocorticoid deficiency and volume depletion 1
• The acidosis results from aldosterone deficiency leading to renal sodium wasting, volume contraction, and impaired hydrogen ion excretion 1
• Compensatory respiratory alkalosis may be present if the patient is hyperventilating in response to the metabolic acidosis 1

Critical Context: ABG Is Not the Diagnostic Focus

The ABG is a supportive finding but should never be used in isolation to diagnose or exclude adrenal insufficiency. The diagnosis hinges on:

• Morning cortisol <250 nmol/L (<9 µg/dL) with elevated ACTH in acute illness is diagnostic of primary adrenal insufficiency 2, 3
• Cosyntropin stimulation test with peak cortisol <500 nmol/L (<18 µg/dL) confirms the diagnosis 2, 3
• Hyponatremia is present in 90% of cases, making it far more sensitive than any ABG finding 2, 3

Important Electrolyte Considerations That Affect ABG Interpretation

• Hyperkalemia occurs in only ~50% of primary adrenal insufficiency cases, so its absence cannot rule out the diagnosis 2, 3
• Hypokalemia can paradoxically occur when severe vomiting or diarrhea is present, masking the expected hyperkalemia from aldosterone deficiency 4, 1, 5
• When hypokalemia coexists with Addison's disease, investigate for concurrent renal tubulopathy or gastrointestinal losses 1, 5

Clinical Pitfalls to Avoid

• Never delay treatment of suspected adrenal crisis to obtain an ABG or any other diagnostic test—give 100 mg IV hydrocortisone immediately plus 0.9% saline at 1 L/hour if the patient is hemodynamically unstable 2, 3, 4
• Do not rely on the presence or absence of hyperkalemia to make or exclude the diagnosis, as electrolyte patterns are highly variable 2, 3, 5
• The combination of severe hyponatremia with normal potassium can mimic SIADH—always perform cosyntropin stimulation testing to exclude adrenal insufficiency before diagnosing SIADH 2, 5

Additional Laboratory Findings Beyond ABG

• Hypoglycemia may be present, particularly in children with adrenal insufficiency 1
• Mild hypercalcemia occurs in 10-20% of cases 2, 3
• Elevated creatinine from prerenal azotemia is common due to volume depletion 2
• Anemia, mild eosinophilia, and lymphocytosis are frequent hematologic findings 3