**Question:** Increased anion gap metabolic acidosis is seen in all except:

A. Diabetic ketoacidosis (DKA)
B. Acidosis due to respiratory failure
C. Acidosis due to lactic acidosis
D. Acidosis due to ketonic compounds

**Core Concept:**
Anion gap is a measure of the difference between the measured and calculated acid-base status in the blood. It is calculated as:

Anion gap = Na+ (in mmoles/L) + Cl- (in mmoles/L) - (Glucose [in mg/dL] x 0.05)

Increased anion gap indicates the presence of unmeasured anions (e.g., ketone bodies, unmeasured acidic compounds) which cause a dissociation of hydrogen ions (H+) from plasma proteins, leading to a decrease in pH and an increase in base excess.

**Why the Correct Answer is Right:**
Increased anion gap is an indicator of the presence of unmeasured anions, which are substances not included in the anion gap calculation. The correct answer (A) refers to Diabetic Ketoacidosis (DKA), which is a condition characterized by the presence of unmeasured anions (ketone bodies) causing acidosis. DKA is typically seen in patients with poorly controlled diabetes mellitus.

**Why Each Wrong Option is Incorrect:**

A. Diabetic ketoacidosis (DKA) causes an increased anion gap due to the presence of unmeasured anions (ketone bodies). It is therefore the correct answer.

B. Acidosis due to respiratory failure (option B) primarily results from an increase in carbon dioxide (CO2) levels, which reduces the anion gap. In respiratory acidosis, the increase in CO2 levels leads to a decrease in plasma bicarbonate concentration, causing a decrease in the anion gap.

C. Acidosis due to lactic acidosis (option C) also results in a decreased anion gap. Lactic acidosis occurs due to impaired oxidative phosphorylation, leading to a decrease in plasma bicarbonate concentration and a decrease in the anion gap.

D. Acidosis due to ketonic compounds (option D) typically results in a decreased anion gap. Ketonic compounds (e.g., ketone bodies) cause a decrease in plasma bicarbonate concentration and lead to a decrease in the anion gap.

**Clinical Pearl:**

An increased anion gap is seen in conditions involving the presence of unmeasured anions, such as in Diabetic ketoacidosis (DKA). A decreased anion gap is seen in conditions like lactic acidosis and respiratory acidosis, where there is an increase in plasma bicarbonate concentration.