Renal Tubular Acidosis in MRCP (1)

As I mentioned earlier in my previous post, there are two main types of metabolic acidosis. These can be either a normal or reduced anion gap type of metabolic acidosis. The causes of reduced anion gap metabolic acidosis are MUD-PILES. Today we are going to discuss the major cause of normal anion gap metabolic acidosis namely RENAL TUBULAR ACIDOSIS. In case you forget,
Anion gap= (Na+K) - (Cl+HCO3)
Normal range= 10-18 mmol/L

In above formula, as you notice, in metabolic acidosis, the value of HCO3 will be reduced, therefore, in a normal anion gap metabolic acidosis, the value of Cl will be increased so that the value of anion gap remains unchanged, therefore, normal anion gap metabolic acidosis also can be named as hyperchloraemic acidosis.

RENAL TUBULAR ACIDOSIS TYPE 1

It is the commonest RTA. It is known as distal RTA. It is due to failure of the kidney to create acid urine because the distal tubule fails to exchange Na for H.

Remember that RTA can be due to either congenital or acquired. For RTA type I causes for acquired one include DISTAL+O

D - Vit D excess
I -Inflammatory/ autoimmune- such as chronic active hepatitis, Sjogren’s syndrome.
S -Sickle Cell Disease
T -Transplanted kidney
A -Amphotericin, analgesics (drugs)
L -Lithium
O -Others- medullary sponge kidney

Remember a few features that are characteristics to distal RTA, they are,

1)Hypercalciuria and risk of stone formation and nephrocalcinosis,
2)Plasma HCO3 tends to be lower than proximal,
3)Urine PH always more than 5.5

to be continued......................