## **Core Concept**
The anion gap is a calculated measure used in clinical medicine to help diagnose metabolic acidosis and other conditions. It represents the difference between the concentrations of major cations (positively charged ions) and anions (negatively charged ions) in the blood, typically calculated as: Anion Gap = [Na+] - ([Cl-] + [HCO3-]). This calculation helps identify unmeasured anions that may be present in cases of metabolic acidosis.

## **Why the Correct Answer is Right**
To calculate the anion gap for this patient:
- Sodium (Na+) = 135 mmol/L
- Chloride (Cl-) = 116 mmol/L
- Bicarbonate (HCO3-) = 14 mmol/L

Using the formula: Anion Gap = [Na+] - ([Cl-] + [HCO3-]) = 135 - (116 + 14) = 135 - 130 = 5.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Without a specific value provided for option A, we cannot directly assess its correctness, but based on the calculation, any option not equal to 5 would be incorrect.
- **Option B:** Similarly, without a value, we cannot assess, but if it's not 5, it's incorrect.
- **Option C:** This option is not provided, but if it were not 5, it would be incorrect based on our calculation.
- **Option D:** This option suggests an anion gap of , which does not match our calculated value of 5.

## **Clinical Pearl / High-Yield Fact**
A normal anion gap ranges from 3 to 10 mmol/L, though this can slightly vary by laboratory. An increased anion gap (>10 mmol/L) often indicates the presence of unmeasured anions, such as in diabetic ketoacidosis, lactic acidosis, or renal failure. A normal anion gap (or "non-anion gap") metabolic acidosis suggests the loss of bicarbonate or the addition of non-anion gap acids.

## **Correct Answer:** . 5