From the Guidelines
Renal tubular acidosis (RTA) is primarily categorized into four main types: Type 1 (distal RTA), Type 2 (proximal RTA), Type 3 (mixed RTA), and Type 4 (hyperkalemic RTA), with each type having distinct pathophysiological characteristics and treatment approaches. The classification of RTA into these types is based on the segment of the nephron that is affected and the nature of the acid-base disturbance 1.
Types of Renal Tubular Acidosis
- Type 1 RTA occurs when the distal tubules cannot properly acidify urine, leading to systemic acidosis with alkaline urine and often hypokalemia.
- Type 2 RTA results from impaired bicarbonate reabsorption in the proximal tubules, causing bicarbonate wasting in urine and metabolic acidosis with hypokalemia.
- Type 3 RTA is a rare combined form showing features of both Type 1 and Type 2, typically seen in carbonic anhydrase II deficiency.
- Type 4 RTA is characterized by aldosterone deficiency or resistance, resulting in hyperkalemia and mild metabolic acidosis.
Treatment Approaches
Treatment varies by type but generally includes alkali therapy (sodium bicarbonate or potassium citrate) to correct acidosis 1. Type 1 often requires potassium supplementation, while Type 4 typically needs potassium restriction and sometimes mineralocorticoid replacement. These disorders occur due to specific defects in renal acid-base handling mechanisms, with each type reflecting dysfunction in different segments of the nephron. It's worth noting that while Bartter syndrome, discussed in 1, shares some similarities with RTA, particularly in terms of renal tubular dysfunction, it is distinct and characterized by salt-losing tubulopathy, polyuria, hypokalemia, and metabolic alkalosis.
From the Research
Types of Renal Tubular Acidosis
The main types of renal tubular acidosis (RTA) are:
- Distal RTA (type 1): characterized by impaired acid excretion 2, 3, 4
- Proximal RTA (type 2): caused by defects in reabsorption of filtered bicarbonate 2, 5, 3, 4, 6
- Hyperkalemic RTA (type 4): caused by abnormal excretion of acid and potassium in the collecting duct 2, 3, 4, 6
- Type 3 RTA: a rare form of the disease with features of both distal and proximal RTA 2, 4
Characteristics of Each Type
- Distal RTA (type 1): inability to acidify the urine below pH 5.5 during systemic acidemia 4
- Proximal RTA (type 2): decreased renal bicarbonate threshold 4
- Hyperkalemic RTA (type 4): may occur as a result of aldosterone deficiency or tubular insensitivity to aldosterone 4
- Combined proximal and distal RTA (type 3): secondary to a reduction in tubular reclamation of bicarbonate and an inability to acidify the urine in the face of severe acidemia 4