Renal tubular acidosis (RTA) is a medical condition that involves an accumulation of acid in the body due to a failure of the kidneys to appropriately acidify the urine. When blood is filtered by the kidney, the filtrate passes through the tubules of the nephron, allowing for exchange of salts, acid equivalents, and other solutes before it drains into the bladder as urine. The metabolic acidosis that results from RTA may be caused either by failure to recover sufficient (alkaline) bicarbonate ions from the filtrate in the early portion of the nephron (proximal tubule) or by insufficient secretion of (acid) hydrogen ions into the latter portions of the nephron (distal tubule). Although a metabolic acidosis also occurs in those with renal insufficiency, the term RTA is reserved for individuals with poor urinary acidification in otherwise well-functioning kidneys. Several different types of RTA exist, which all have different syndromes and different causes.
The word acidosis refers to the tendency for RTA to lower the blood's pH. When the blood pH is below normal (7.35), this is called acidemia. The metabolic acidosis caused by RTA is a normal anion gap acidosis.
An overview of types 1, 2, and 4 is presented below (type 3 is usually excluded from modern classifications):
| Type | Type 1 | Type 2 | Type 4 |
|---|---|---|---|
| Location | Distal tubules | Proximal tubules | Adrenal |
| Acidosis? | Yes (severe) | Yes | Mild when present |
| Potassium | Hypokalemia | Hypokalemia | Hyperkalemia |
| Pathophysiology | Failure of H+ secretion by the α intercalated cells | Failed HCO3− reabsorption from the urine by the proximal tubular cells | Deficiency of aldosterone, or a resistance to its effects, (hypoaldosteronism or pseudohypoaldosteronism) |
Read more about Renal Tubular Acidosis: Type 1-Distal RTA, Type 2-Proximal RTA, Type 3 RTA-Combined Proximal and Distal RTA, Type 4 RTA, History, See Also