Understanding Type-1 Renal Tubular Acidosis

Type-1 Renal Tubular Acidosis (RTA), also known as distal RTA, involves impaired acid secretion by the kidney's distal tubules. This leads to a buildup of acid in the body.

Key Features of Type-1 RTA

Common characteristics of Type-1 RTA:

• Impaired H+ Secretion: The distal tubules cannot effectively secrete hydrogen ions (H+).
• High Urine pH: Difficulty in acidifying urine, resulting in a urine pH typically exceeding 5.5 (mathematical expression: pH > 5.5).
• Hypokalemia: Characterized by low serum potassium levels (Option 3 is a feature).
• Normal Anion Gap Metabolic Acidosis: The metabolic acidosis typically presents with a normal anion gap. The body compensates by increasing chloride (Cl-) reabsorption to maintain electrical balance.

Identifying Non-Features of Type-1 RTA

We need to identify the option that is not a characteristic of Type-1 RTA.

• Option 1 (Lower tubule re-absorption of calcium): While related issues like hypercalciuria occur, this isn't the primary excluded feature.
• Option 2 (Defective bicarbonate absorption in distal tubule): The main defect is distal H+ secretion, not distal bicarbonate absorption.
• Option 3 (Low serum potassium level): This is a known feature (hypokalemia).
• Option 4 (Increased anion gap): This is the correct choice because Type-1 RTA causes a normal anion gap metabolic acidosis, not an increased one. An increased anion gap points to other underlying causes of acidosis.

Therefore, an increased anion gap is not a feature of Type-1 RTA.