What is the workup for metabolic alkalosis?

Workup for Metabolic Alkalosis

The diagnostic workup for metabolic alkalosis should include assessment of acid-base status, serum electrolytes, urinary chloride excretion, and evaluation of volume status to determine the underlying cause and guide appropriate treatment. 1

Initial Laboratory Evaluation

• Obtain blood gas analysis (arterial or venous) to confirm metabolic alkalosis (pH >7.43, bicarbonate >26 mmol/L) 1, 2
• Measure serum electrolytes including sodium, potassium, chloride, and bicarbonate 1, 3
• Assess renal function with serum creatinine and BUN 3
• Check urinary chloride concentration to differentiate between chloride-responsive (urinary Cl <10 mEq/L) and chloride-resistant (urinary Cl >20 mEq/L) metabolic alkalosis 2, 4
• Measure serum magnesium levels, as hypomagnesemia often accompanies metabolic alkalosis 3
• Consider measuring plasma renin and aldosterone levels if hyperaldosteronism is suspected 1, 2

Clinical Assessment

• Evaluate volume status (vital signs, orthostatic changes, skin turgor, mucous membranes) to determine if hypovolemic, euvolemic, or hypervolemic 1, 2
• Assess for signs of potassium depletion (muscle weakness, cardiac arrhythmias) 4
• Review medication history, particularly use of diuretics, laxatives, or alkali ingestion 1, 4
• Inquire about symptoms of vomiting, nasogastric suction, or other gastrointestinal losses 2, 4

Diagnostic Algorithm Based on Urinary Chloride

Chloride-Responsive Metabolic Alkalosis (Urinary Cl <10 mEq/L)

• Consider:
  • Vomiting or nasogastric suction 2, 4
  • Recent diuretic use (now discontinued) 1
  • Post-hypercapnic state 4

Chloride-Resistant Metabolic Alkalosis (Urinary Cl >20 mEq/L)

• Consider:
  • Current diuretic use 1, 4
  • Primary hyperaldosteronism 2
  • Bartter syndrome or Gitelman syndrome 5, 1
  • Cushing syndrome 4
  • Severe hypokalemia 1, 4

Additional Diagnostic Tests

• Renal ultrasound to assess for nephrocalcinosis or kidney stones, particularly if Bartter syndrome is suspected 5, 3
• If Bartter syndrome is suspected, consider genetic testing for definitive diagnosis 5
• In patients with heart failure and metabolic alkalosis, evaluate cardiac function and consider cardiology consultation 6, 7
• For patients with unexplained alkalosis, especially with a history of polyhydramnios and premature birth, consider Bartter syndrome in the differential diagnosis 1

Common Pitfalls to Avoid

• Failing to measure urinary chloride, which is essential for determining the cause and appropriate treatment 2, 4
• Overlooking medication-induced causes, particularly diuretics 1, 7
• Not considering rare genetic causes like Bartter syndrome in patients with persistent unexplained metabolic alkalosis 5, 1
• Treating the alkalosis without addressing the underlying cause 7, 4
• Administering large volumes of non-chloride containing fluids, which may worsen the alkalosis 2, 8

By following this systematic approach to the workup of metabolic alkalosis, clinicians can identify the underlying cause and implement appropriate treatment strategies to correct the acid-base disturbance and prevent complications.