Renal tubular acidosis

Question 1

What is type I renal tubular acidosis?

Answer 1

Distal hypocholraemic acidosis

Disorder where the tubules are unable to secrete hydrogen ions, which causes secondary hyperaldosteronism and results in hypokalaemia and hypochloraemia

Question 2

What are causes of type I RTA?

Answer 2

• Autoimmune disease - Sjogren’s. SLE, CAH
• Drugs - NSAIDS. amphotericin
• Nephrocalcinosis
• Obstructive nephropathy

Question 3

What is type II RTA?

Answer 3

Proximal hypokalaemic, hypochloraemic acidsosis

The principle abnormality is the inability of the proximal tubular cells to reabsorb bicarbonate. It is associated with with generalised defect of reabsorption, known as fanconi syndrome.

Proximal tubule cannot reabsorb the increased filtered load -> delivered to distal tubule and is unable to be reabsorbed -> urinary loss of HCO3

Question 4

What type of acisosis occurs in renal tubular acidosis?

Answer 4

Metabolic acidosis with normal anion gap

Question 5

What are causes of type II RTA?

Answer 5

• Hereditary (most common, diagnosed in infants and children)
• Fanconi syndrome
• Vitamin D deficiency
• Cystinosis
• Lead nephropathy
• Amyloidosis
• Medullary cystic disease

Question 6

Why does acidosis occur in type II RTA?

Answer 6

Proximal tubule cannot reabsorb the increased filtered load -> delivered to distal tubule and is unable to be reabsorbed -> urinary loss of HCO3

Question 7

Why does acidosis occur in type I RTA?

Answer 7

Reduced secretion of H+ in distal tubule results inability to maximally acidify the urine

Question 8

What investigations might you do in someone with suspected renal tubular acidosis?

Answer 8

• Bloods - U+E’s, ABG + anion gap
• Other - Urinary pH, Sodium bicarbonate loading

Question 9

What might you find on serum bicarbonate in type I RTA?

Answer 9

Low

Question 10

What might you find on investigation of serum bicarbonate in type II RTA?

Answer 10

Low

Question 11

What might you find on investigation of serum chloride levels in those with RTA?

Answer 11

Hyperchloraemia

Question 12

What might you find on investigation of urinary pH in someone with type I RTA?

Answer 12

pH > 5.5 despite severe acidaemia

Question 13

What might you find on investigation of urinary bicarbonate when loading someone with bicarbonate in type I RTA?

Answer 13

Increased urinary bicarbonate

Question 14

What might you expect to see on investigation of potassium in someone with type I RTA?

Answer 14

Hypokalaemia - secondary to secondary hyperaldosteronism

Question 15

What might you expect to see on investigation of serum potassium in someone with Type II RTA?

Answer 15

Hyperkalaemia

Question 16

What might you expect to see in bicarbonate loading in someone with type II RTA?

Answer 16

Urinary pH drops < 5.5

Question 17

What is type IV renal tubular acidosis?

Answer 17

Hyperkalaemic distal RTA

Seen in cases where there is a cause aldosterone deficiency or aldosterone resistance.

Question 18

Why does type IV RTA occur?

Answer 18

Defect in cation-exchange in the distal tubule with reduced secretion of both H+ and K+

Physiological reduction in proximal tubular ammonium excretion (impaired ammoniagenesis) due to to hypoaldosteronism, results in a decrease in urine buffering capacity

Question 19

What are causes of type IV RTA?

Answer 19

Aldosterone deficiency (hypoaldosteronism)

• Primary
• Secondary / hyporeninemic (including diabetic nephropathy)

Aldosterone resistance

• Drugs: NSAIDs, ACE inhibitors and ARBs, Eplerenone, Spironolactone, Trimethoprim, Pentamidine
• Pseudohypoaldosteronism

Question 20

What might you find on investigation of type IV RTA?

Answer 20

• Mild metabolic acidosis
• Plasma HCO3 usually > 15mmol/L
• Hyperkalaemia