Renal tubular acidosis

Question 1

What is it?

Answer 1

Renal tubular acidosis is where there is a metabolic acidosis due to pathology in the tubules of the kidney. The tubules are responsible for balancing the hydrogen and bicarbonate ions between the blood and urine and maintaining a normal pH. There are four types each with different pathophysiology.

Type 1 and type 4 are the two that may come up in your exams and are most relevant to clinical practice.

Question 2

Type 1 Renal Tubular Acidosis causes?

Answer 2

Type 1 renal tubular acidosis is due to pathology in the distal tubule. The distal tubule is unable to excrete hydrogen ions.

There are many causes:

Genetic. There are both autosomal dominant and recessive forms.
Systemic lupus erythematosus
Sjogren’s syndrome
Primary biliary cirrhosis
Hyperthyroidism
Sickle cell anaemia
Marfan’s syndrome

Question 3

Type 1 Renal Tubular Acidosis presentation?

Answer 3

Failure to thrive in children
Hyperventilation to compensate for the metabolic acidosis
Chronic kidney disease
Bone disease (osteomalacia)

Question 4

Type 1 Renal Tubular Acidosis results and treatment?

Answer 4

Hypokalaemia
Metabolic acidosis
High urinary pH (above 6)

Treatment is with oral bicarbonate. This corrects the other electrolyte imbalances.

Question 5

Type 2 Renal Tubular Acidosis

Answer 5

Type 2 renal tubular acidosis is due to pathology in the proximal tubule. The proximal tubule is unable to reabsorb bicarbonate from the urine into the blood. Excessive bicarbonate is excreted in the urine. Fanconi’s syndrome is the main cause.

Question 6

Type 2 results and treatment?

Answer 6

Results:

Hypokalaemia
Metabolic acidosis
High urinary pH (above 6)

Treatment is with oral bicarbonate.

Question 7

Type 4 Renal Tubular Acidosis

Answer 7

Type 4 renal tubular acidosis is caused by reduced aldosterone. This is probably the most common cause of renal tubular acidosis and the most likely to turn up in your exams and clinical practice.

This can be due to adrenal insufficiency, medications such as ACE inhibitors and spironolactone or systemic conditions that affect the kidneys such as systemic lupus erythematosus, diabetes or HIV.

Question 8

Type 4 results and treatment ?

Answer 8

Hyperkalaemia
High chloride
Metabolic acidosis
Low urinary pH

Management is with fludrocortisone. Sodium bicarbonate and treatment of the hyperkalaemia may also be required.