Pseudo-Metabolic Alkalosis: A Hidden Laboratory Pitfall With Elevated LDH.
Tulsi Patel, Kevin Wortman, Nabil Merchant
✦ AI-curated · Sources linked
Case in brief
A 33-year-old man presented with progressive exertional dyspnea, syncope, and paresthesia. Testing showed pancytopenia, macrocytosis, LDH >3600 U/L, low haptoglobin, and vitamin B₁₂ <68 pg/mL, consistent with pernicious anemia. Chemistry panels repeatedly reported serum bicarbonate >45 mmol/L, suggesting metabolic alkalosis, but arterial and venous blood gases showed normal pH and bicarbonate. The discrepancy was attributed to interference from extreme LDH activity in the chemistry assay, rather than a true acid–base disturbance.
What made this case unusual
Marked LDH elevation associated with severe vitamin B₁₂ deficiency produced pseudohyperbicarbonatemia on routine chemistry testing, while blood gas-derived bicarbonate remained normal.
Diagnostic / clinical pearl
When a markedly elevated chemistry-panel bicarbonate conflicts with the clinical picture, confirm the acid–base status with blood gas analysis; extreme LDH can interfere with enzymatic bicarbonate assays.
Why it matters
Recognizing this assay interference can prevent a false diagnosis of metabolic alkalosis and unnecessary intervention.