Question:
A 45-year-old man is brought to the emergency department with confusion and rapid breathing after being found unconscious at home. Arterial blood gas analysis shows pH 7.10 and an anion gap of 18. Toxicology screening is pending. Which of the following substances is least likely to be responsible for his condition?
A 45-year-old man is brought to the emergency department with confusion and rapid breathing after being found unconscious at home. Arterial blood gas analysis shows pH 7.10 and an anion gap of 18. Toxicology screening is pending. Which of the following substances is least likely to be responsible for his condition?
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Anion Gap = $[Na^+] - ([Cl^-] + [HCO_3^-])$.
Toxic alcohols (Methanol, Ethylene glycol) are unique because they often cause BOTH a High Anion Gap AND a High Osmolar Gap.
Toxic alcohols (Methanol, Ethylene glycol) are unique because they often cause BOTH a High Anion Gap AND a High Osmolar Gap.
Updated On: Sep 3, 2026
- Ethanol
- Ethylene glycol
- Lithium
- Methanol
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The Correct Option is C
Solution and Explanation
Concept:
The patient presents with an altered mental status, tachypnea (rapid breathing indicating Kussmaul respirations to blow off CO2), severe acidemia (pH 7.10), and an elevated anion gap (Normal AG is roughly 8-12).
This establishes a diagnosis of High Anion Gap Metabolic Acidosis (HAGMA).
The question asks us to identify which of the provided toxicological substances is LEAST likely to cause HAGMA.
Explanation:
• The classic mnemonic for the causes of High Anion Gap Metabolic Acidosis is MUDPILES:
• M = Methanol
• U = Uremia
• D = Diabetic Ketoacidosis (DKA)
• P = Propylene glycol Paracetamol
• I = Iron Isoniazid
• L = Lactic acidosis
• E = Ethylene glycol Ethanol (via alcoholic ketoacidosis)
• S = Salicylates
• Based on this differential, Methanol (Option D) metabolizes to formic acid, causing severe HAGMA.
• Ethylene glycol (Option B) metabolizes to glycolic and oxalic acids, causing profound HAGMA.
• Ethanol (Option A) overdose can induce alcoholic ketoacidosis (secondary to starvation and hepatic glycogen depletion), leading to a buildup of beta-hydroxybutyrate and subsequent HAGMA.
• Lithium (Option C) toxicity primarily causes neurological symptoms (tremors, ataxia, encephalopathy) and renal dysfunction (Nephrogenic Diabetes Insipidus). It does not inherently cause a High Anion Gap Metabolic Acidosis.
• Therefore, Lithium is the toxic agent among the choices that does not fit the ABG profile.
Final answer:
Lithium does not cause high anion gap metabolic acidosis and is the least likely culprit.
The patient presents with an altered mental status, tachypnea (rapid breathing indicating Kussmaul respirations to blow off CO2), severe acidemia (pH 7.10), and an elevated anion gap (Normal AG is roughly 8-12).
This establishes a diagnosis of High Anion Gap Metabolic Acidosis (HAGMA).
The question asks us to identify which of the provided toxicological substances is LEAST likely to cause HAGMA.
Explanation:
• The classic mnemonic for the causes of High Anion Gap Metabolic Acidosis is MUDPILES:
• M = Methanol
• U = Uremia
• D = Diabetic Ketoacidosis (DKA)
• P = Propylene glycol Paracetamol
• I = Iron Isoniazid
• L = Lactic acidosis
• E = Ethylene glycol Ethanol (via alcoholic ketoacidosis)
• S = Salicylates
• Based on this differential, Methanol (Option D) metabolizes to formic acid, causing severe HAGMA.
• Ethylene glycol (Option B) metabolizes to glycolic and oxalic acids, causing profound HAGMA.
• Ethanol (Option A) overdose can induce alcoholic ketoacidosis (secondary to starvation and hepatic glycogen depletion), leading to a buildup of beta-hydroxybutyrate and subsequent HAGMA.
• Lithium (Option C) toxicity primarily causes neurological symptoms (tremors, ataxia, encephalopathy) and renal dysfunction (Nephrogenic Diabetes Insipidus). It does not inherently cause a High Anion Gap Metabolic Acidosis.
• Therefore, Lithium is the toxic agent among the choices that does not fit the ABG profile.
Final answer:
Lithium does not cause high anion gap metabolic acidosis and is the least likely culprit.
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