Differential Diagnosis for CO2 16, Anion Gap 19, with Nausea and Vomiting

• Single Most Likely Diagnosis
  • Metabolic Acidosis due to Diarrhea or Gastrointestinal Bypass: The elevated anion gap and low CO2 (bicarbonate) levels suggest a metabolic acidosis. Nausea and vomiting can lead to loss of bicarbonate, contributing to the acidosis. However, the presence of an elevated anion gap suggests that there might be an additional component such as lactic acidosis or ketoacidosis, especially if the vomiting is severe enough to cause dehydration and subsequent lactic acid production.
• Other Likely Diagnoses
  • Diabetic Ketoacidosis (DKA): Although typically associated with hyperglycemia, DKA can present with an elevated anion gap metabolic acidosis, nausea, vomiting, and variable glucose levels. The anion gap is elevated due to the production of ketone bodies.
  • Lactic Acidosis: This can occur due to tissue hypoperfusion (e.g., from severe dehydration caused by vomiting), leading to an elevated anion gap metabolic acidosis. Nausea and vomiting can be symptoms of the underlying cause of lactic acidosis.
  • Renal Tubular Acidosis (RTA): Certain types of RTA can present with a normal anion gap metabolic acidosis, but some forms, especially those with a significant tubular damage, might have an elevated anion gap. However, RTA is less likely given the acute presentation with nausea and vomiting.
• Do Not Miss Diagnoses
  • Ethylene Glycol or Methanol Poisoning: These can cause an elevated anion gap metabolic acidosis and are critical to diagnose early due to their potential for severe morbidity and mortality. Nausea and vomiting can be part of the presentation, although the history of ingestion might not always be available.
  • Salicylate Toxicity: Aspirin overdose can lead to an elevated anion gap metabolic acidosis, tinnitus, and gastrointestinal symptoms like nausea and vomiting. It's crucial to consider this diagnosis due to its potential severity and the need for specific treatment.
• Rare Diagnoses
  • Pyroglutamic Acidemia: A rare cause of elevated anion gap metabolic acidosis, often associated with acetaminophen use, malnutrition, or critical illness. It's less likely but should be considered in the appropriate clinical context.
  • Maple Syrup Urine Disease or Other Organic Acidemias: These are rare genetic disorders that can cause elevated anion gap metabolic acidosis. They are more commonly diagnosed in pediatric patients but can present at any age, especially during metabolic stress.