Question

A 45-year-old man is evaluated for electrolyte imbalance: \(Na^+ = 130\) mmol/L, \(Cl^- = 84\) mmol/L, \(HCO_3^- = 16\) mmol/L. What is his anion gap?

• A. 26
• B. 30
• C. 18
• D. 22

Hint:

Anion gap formula: \[ AG = Na^+ - (Cl^- + HCO_3^-) \]

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The objective is to calculate the serum anion gap based on provided clinical laboratory data.
The anion gap is an essential tool in clinical medicine used to narrow down the differential diagnosis of metabolic acidosis.
Step 2: Key Formula or Approach:
The serum anion gap (SAG) represents the difference between measured cations and measured anions in the blood. The standard calculation formula is:
\[ \text{Anion Gap} = [Na^+] - ([Cl^-] + [HCO_3^-]) \]
Step 3: Detailed Explanation:

Step-by-step Calculation:

Identify the given electrolyte values: Sodium ($Na^+$) = 130, Chloride ($Cl^-$) = 84, and Bicarbonate ($HCO_3^-$) = 16.

First, calculate the total sum of the measured anions:
\[ 84 + 16 = 100 \text{ mmol/L} \]

Subtract this sum from the measured Sodium concentration:
\[ 130 - 100 = 30 \text{ mmol/L} \]


Clinical Interpretation:

A normal anion gap is typically between 8 and 12 mmol/L.

The calculated value of 30 indicates a significantly elevated anion gap.

This signifies High Anion Gap Metabolic Acidosis (HAGMA), suggesting the presence of unmeasured anions such as ketoacids, lactate, or toxins like methanol or salicylates.


Step 4: Final Answer:
The patient has an anion gap of 30, which is Option B.