Renal Tubular Acidosis Explained

I hate really hate studying this material but once you understand it, it becomes very easy to memorize.

Remember in renal tubular acidosis (RTA) there is normal anion gap.  [Na - (Cl - HCO3)] = 6-12.
Proximal part is the upper part of the renal tubules, while the distal part is the end part of the tubules.
 
Type II (Proximal)

1. Pathophysiology: Decreased ability of the proximal kidney tubules to reabsorb most of the filtered bicarbonate because normally bicarbonate is filtered at the proximal tube.
2. Urine pH: Variable: Urine pH is basic until bicarbonate is depleted, the it is acidic (less than 5.5)
3. Blood K+ level: Low
4. Kidney Stones: No
5. Associations
6. Diagnosis: Infuse bicarbonate and evaluate the urine pH
7. Treatment: Thiazide because it causes volume depletion, which will enhance bicarbonate reabsorption.

Type I (Distal)

1. Pathophysiology: Distal tubule is damaged so it is unable to generate bicarbonate. Without bicarbonate, H+ cannot be secreted in the tubule to the urine, raising urine pH.
2. Urine pH: Urine pH more than 5.5.
3. Blood K+ Level: Low
4. Kidney Stones: Yes
5. Associations
   
   • Amphotericin use
   • Lithium Use
   • Sickle Cell Disease
   • Autoimmune Diseases (SLE, Sjorgen Syndrome, Rheumatoid Arthritis, etc)
6. Diagnosis: Infuse acid
7. Treatment: Bicarbonate to be absorbed in the proximal tubule, because majority of the bicarbonate is absorbed there.
   

Type IV (Distal)

1. Pathophysiology: Decreased or diminished effect of aldosterone at the kidney tubule. Loss of sodium and retention of potassium and hydrogen ions.
2. Urine pH: Less than 5.5
3. Blood K+ level: High
4. Kidney Stones: No
5. Associations
   
   • Diabetes
   • Addison's Disease
   • NSAIDs
6. Diagnosis: Urine salt loss, despite sodium restricted diet
7. Treatment: Fludrocortisone