RENAL TUBULAR ACIDOSIS

Question 1

Describe the 4 forms of renal tubular acidosis

Answer 1

Type 1: Distal RTA: H+ not secreted from collecting duct

Type 2: Proximal RTA: HCO₃ not reabsorbed from PCT​

Type 3: Mixed

Type 4: Hyperkalaemic RTA: Aldosterone not responded to

Question 2

Why are there low potassium levels in type 1 renal tubular acidosis?

Answer 2

Distal tubules fail to secrete hydrogen and therefore potassium is not reabsorbed from urine

Question 3

Why is TY1 (distal) renal tubular acidosis associated with chronic kidney stones?

Answer 3

• Alkaline urine precipitates stones
• Acidosis increases calcium resorption from bones
• Acidosis suppresses reabsorption of calcium from urine

Question 4

What condition should you consider in someone with Sjogren’s syndrome or rheumatoid arthritis or on amphotericin B developing metabolic acidosis?

Answer 4

Type 1 (distal) RTA

Question 5

How do you treat a distal RTA?

Answer 5

Sodium bicarbonate

Question 6

Why do distal RTAs cause very low serum bicarbonate levels?

Answer 6

Acid cannot be secreted in the distal tubules causing HCO3 levels to dramatically drop

Question 7

Which type of RTA causes a hyperkalaemia? Explain why

Answer 7

Type IV RTA: hypoaldosteronism

Decreased excretion of potassium due to distal tubular failure to respond to aldosterone

Question 8

Explain why there is a lower urinary pH in type 4 RTA

Answer 8

• Hyperkalaemia causes decreased excretion of ammonium in urine
• This reduces buffering available in urine and decreases pH

Question 9

A diabetic on ibuprofen comes in with elevated potassium, low bicarbonate and low urinary pH has which condition? Explain why this is caused

Answer 9

Type IV RTA

Low renin activity is common in diabetics and results in hypoaldosteronism

NSAIDs also impair renin release

HIGH YIELD

Question 10

People with multiple myeloma are at increased risk of which type of RTA?

Answer 10

Type 2 (proximal): impaired HCO₃ reabsorption in proximal tubule