Differential Diagnosis for Decreased CO2 and Elevated Anion Gap
Single Most Likely Diagnosis
- Diabetic Ketoacidosis (DKA): This condition is characterized by hyperglycemia, metabolic acidosis, and the presence of ketones in the blood. The metabolic acidosis leads to a decreased CO2 level (as the body tries to compensate by increasing respiratory rate and depth, thus blowing off CO2) and an elevated anion gap due to the accumulation of ketones and other organic acids.
Other Likely Diagnoses
- Lactic Acidosis: This can occur due to tissue hypoxia (from any cause, including shock, sepsis, or carbon monoxide poisoning), leading to the production of lactic acid. The increased lactic acid levels decrease CO2 and increase the anion gap.
- Renal Failure: Acute or chronic renal failure can lead to the accumulation of organic acids, which in turn can cause metabolic acidosis with an elevated anion gap and decreased CO2.
- Toxic Ingestions (e.g., Salicylates, Ethylene Glycol, Methanol): Certain toxic ingestions can lead to metabolic acidosis with an elevated anion gap. For example, salicylate toxicity can directly contribute to an increased anion gap, while ethylene glycol and methanol poisonings lead to the production of organic acids.
Do Not Miss Diagnoses
- Sepsis: Although sepsis can lead to a variety of acid-base disturbances, it is crucial not to miss, as it can cause lactic acidosis and thus an elevated anion gap and decreased CO2.
- Severe Dehydration: Leading to lactic acidosis due to poor tissue perfusion, which can result in an elevated anion gap and decreased CO2.
Rare Diagnoses
- Ketone Body Production Disorders: Rare genetic disorders affecting the metabolism of fatty acids and ketone bodies, leading to the accumulation of organic acids and thus an elevated anion gap and decreased CO2.
- Pyroglutamic Acidemia: A rare condition caused by an inborn error of metabolism leading to the accumulation of pyroglutamic acid, which contributes to an elevated anion gap metabolic acidosis.
- Isopropyl Alcohol Toxicity: Though less common than ethanol or methanol, isopropyl alcohol (isopropanol) ingestion can lead to metabolic acidosis with an elevated anion gap due to the formation of acetone and other organic acids.