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Difficulty: EasyNephrology

A newly admitted 19-year-old male with a history of type 1 diabetes mellitus is evaluated on the medical ward for persistent nausea, recurrent vomiting, and diffuse abdominal pain. The patient admits to missing his insulin doses over the past three days. The following initial serum chemistry panel is obtained:

* Sodium: 138 mEq/L
* Potassium: 5.1 mEq/L
* Chloride: 99 mEq/L
* Bicarbonate: 14 mEq/L
* Blood urea nitrogen: 28 mg/dL
* Creatinine: 1.2 mg/dL
* Glucose: 485 mg/dL

Calculate the patient's serum anion gap in mEq/L.

Answer: 25 mEq/L

Answer

25 mEq/L
The patient's clinical presentation and laboratory results indicate diabetic ketoacidosis. To evaluate the severity and nature of the metabolic acidosis, the anion gap is calculated using the formula AG=Na+−(Cl−+HCO3−)AG = Na^+ - (Cl^- + HCO_3^-). Using the provided serum values: 138−(99+14)=25138 - (99 + 14) = 25 mEq/L. A normal anion gap typically ranges between 8 and 12 mEq/L, confirming that this patient has a significantly elevated high anion gap metabolic acidosis (HAGMA).

Step-by-Step Solution

1
Identify the standard formula for calculating the serum anion gap.
AG=Na+−(Cl−+HCO3−)AG = Na^+ - (Cl^- + HCO_3^-)
The anion gap evaluates the unmeasured anions in the blood by subtracting the sum of the primary measured anions (chloride and bicarbonate) from the primary measured cation (sodium).
2
Extract the necessary laboratory values from the clinical vignette.
Na+=138Na^+ = 138 mEq/L, Cl−=99Cl^- = 99 mEq/L, and HCO3−=14HCO_3^- = 14 mEq/L.
These specific serum electrolytes are required to perform the calculation.
3
Perform the subtraction using the extracted values.
138−(99+14)=25138 - (99 + 14) = 25 mEq/L.
The result yields the final unmeasured anion concentration, which is significantly elevated and consistent with a high anion gap metabolic acidosis.

Key Concept

Calculation of the serum anion gap in the evaluation of metabolic acidosis.
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Topics

Nephrology

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