Unidentified anion gap metabolic acidosis

Area of Science:

• Pediatric Critical Care
• Clinical Chemistry
• Toxicology

Background:

• Nonketotic hyperglycinemia (NKH) is a rare metabolic disorder.
• Anion gap metabolic acidosis requires prompt diagnosis and management.
• Dietary supplements can have unmonotic effects.

Observation:

• A 35-month-old female with NKH presented with severe metabolic acidosis, seizures, and hypoglycemia.
• Standard diagnostic mnemonics for high anion gap metabolic acidosis were initially unrevealing.
• Elevated benzoic acid levels were detected via GC-MS, correlating with sodium benzoate supplementation.

Findings:

• High benzoic acid concentrations (over 2000 μg/mL) were identified in the patient's urine.
• Benzoic acid was determined to be the cause of the anion gap metabolic acidosis.
• Benzoic acid interfered with the salicylate assay, leading to a falsely elevated salicylate level.

Implications:

• This case highlights the importance of considering supplement toxicity in pediatric metabolic emergencies.
• Accurate laboratory testing interpretation is crucial, especially when unexpected results arise.
• Awareness of benzoic acid's potential to interfere with salicylate assays is important for clinicians.