The question asks to identify the disorder that does not typically cause an increased anion gap among the given options.

Anion Gap Disorders Explained

The anion gap (AG) is calculated as: $ \text{AG} = [\text{Na}^+] - ([\text{Cl}^-] + [\text{HCO}_3^-]) $ An increased anion gap indicates the presence of unmeasured anions in the blood, often due to organic acids.

Analysis of Options

• Diabetic ketoacidosis (DKA): Characterized by the accumulation of ketone bodies (ketoacids), which are unmeasured anions. This leads to a metabolic acidosis with an increased anion gap.
• Starvation ketosis: Prolonged fasting leads to ketone body production, similar to DKA, resulting in a metabolic acidosis with an increased anion gap.
• Renal tubular acidosis (RTA): This condition involves impaired kidney function in excreting acids or conserving bicarbonate. Most forms of RTA (Type 1, Type 2) cause a metabolic acidosis where chloride levels rise to compensate for bicarbonate loss, maintaining a normal anion gap.
• Lactic acidosis: Caused by the buildup of lactic acid, a strong organic acid. This results in a severe metabolic acidosis with a significantly increased anion gap.

Identifying the Exception

Based on the analysis, Diabetic ketoacidosis, Starvation ketosis, and Lactic acidosis all lead to an accumulation of unmeasured anions, thus increasing the anion gap. Renal tubular acidosis, particularly Type 1 and Type 2, is primarily characterized by a normal anion gap metabolic acidosis.

Therefore, Renal tubular acidosis is the exception.