Renal tubular acidosis

Question 1

What is Renal Tubular Acidosis (RTA)?

Answer 1

RTA involves metabolic acidosis due to pathology in the tubules of the kidneys, affecting the balance of hydrogen ions (H+) and bicarbonate ions (HCO3–) between the blood and urine.

Question 2

What are the types of Renal Tubular Acidosis (RTA) and their characteristics?

Answer 2

Type 1: Distal tubule cannot excrete hydrogen ions, leading to high urinary pH and low serum potassium.
Type 2: Proximal tubule cannot reabsorb bicarbonate, leading to high urinary pH and low serum potassium.
Type 4: Low or impaired aldosterone, leading to low urinary pH and high serum potassium.

Question 3

What is the key difference between Type 1 and Type 4 Renal Tubular Acidosis?

Answer 3

Both involve inadequate hydrogen excretion in the distal tubules, but Type 1 involves hypokalaemia and Type 4 involves hyperkalaemia.

Question 4

What happens in Type 1 Renal Tubular Acidosis (Distal RTA)?

Answer 4

The distal tubule cannot excrete hydrogen ions, leading to:
* High urinary pH (due to absence of hydrogen ions)
* Metabolic acidosis (due to retained hydrogen ions in blood)
* Hypokalaemia (due to failure of H+/K+ ATPase)

Question 5

What conditions can cause Type 1 Renal Tubular Acidosis?

Answer 5

• Genetic factors (autosomal dominant or recessive)
• Systemic lupus erythematosus
• Sjögren’s syndrome
• Primary biliary cholangitis
• Hyperthyroidism
• Sickle cell anaemia
• Marfan’s syndrome

Question 6

What are the symptoms of Type 1 Renal Tubular Acidosis?

Answer 6

• Failure to thrive in children
• Recurrent UTIs (due to alkaline urine)
• Bone disease (rickets or osteomalacia)
• Muscle weakness
• Arrhythmias (due to hypokalaemia)

Question 7

How is Type 1 Renal Tubular Acidosis treated?

Answer 7

Treatment involves oral bicarbonate to correct acidosis and electrolyte imbalances.

Question 8

What happens in Type 2 Renal Tubular Acidosis (Proximal RTA)?

Answer 8

The proximal tubule cannot reabsorb bicarbonate, leading to:
* High urinary pH (due to excess bicarbonate in urine)
* Metabolic acidosis (due to inadequate bicarbonate in blood)
* Hypokalaemia (due to potassium loss with bicarbonate)

Question 9

What are the key causes of Type 2 Renal Tubular Acidosis?

Answer 9

• Inherited (autosomal dominant or recessive)
• Multiple myeloma
• Fanconi’s syndrome

Question 10

How is Type 2 Renal Tubular Acidosis treated?

Answer 10

Treatment involves oral bicarbonate.

Question 11

What is Type 3 Renal Tubular Acidosis?

Answer 11

Type 3 RTA (mixed RTA) is a combination of Type 1 and Type 2, with pathology in both the proximal and distal tubules. It is rare and unlikely to appear in exams.

Question 12

What happens in Type 4 Renal Tubular Acidosis (Hyperkalaemic RTA)?

Answer 12

Type 4 RTA is caused by reduced aldosterone, leading to:
* Metabolic acidosis (due to retained hydrogen ions)
* Hyperkalaemia (due to retained potassium)
* Low urinary pH (due to reduced ammonia production in response to hyperkalaemia)

Question 13

What causes Type 4 Renal Tubular Acidosis?

Answer 13

• Adrenal insufficiency
• Diabetic nephropathy
• Medications (e.g., ACE inhibitors, spironolactone, eplerenone)

Question 14

How is Type 4 Renal Tubular Acidosis treated?

Answer 14

Treatment is targeted at the underlying cause, with options including:
* Fludrocortisone (for aldosterone deficiency)
* Oral bicarbonate
* Treatment of hyperkalaemia