Renal tubular acidosis is a kidney disorder that leads to acidification of the blood. Since there are several mechanisms which, if defective, can lead to metabolic acidosis, the disease is divided into four classes. A distinction is made between distal (type I), proximal (type II), a mixed form of type I and type II (i.e. type III) and hyperkalemic (type IV) acidosis.
What is renal tubular acidosis?
Renal tubular acidosis usually results from defective antiporters and transport channels in the epithelial cells. Specialized channels in the epithelial cells, through which certain molecules can be exchanged with one another, are referred to as antiporters. In order to be able to understand the exact cause of the defect, the resorption processes must first be explained. For what does kns stand for, please visit biotionary.com.
The resorption processes in the nephron tubule begin with the exchange of hydrogen ions (H+) from the adjacent epithelial cells with sodium from the tubule. This process takes place via the sodium/hydrogen antiporter. A molecule of bicarbonate (bicarbonate, HCO3) is too large to be absorbed via an antiporter. Therefore, bicarbonate must first react with the hydrogen ion that has been exchanged with sodium to form carbonic acid.
The reaction is chemically described as HCO3 + H+ = H2CO3. The carbonic acid then breaks down into water (H2O) and carbon dioxide (CO2). Carbon dioxide can escape through the cell wall and triggers a reverse reaction within the epithelial cell, which again takes place in two steps. First, carbon dioxide and water react to form carbonic acid (CO2 + H20 = H2CO3).
The carbonic acid is now split into bicarbonate and a hydrogen ion (H2CO3 = HCO3 + H+). The bicarbonate molecule has now arrived in the epithelial cell via several chemical reactions and can be taken back into the bloodstream via the sodium bicarbonate cotransporter (NBC1).
Type I renal tubular acidosis is usually caused by a defective sodium hydrogen antiporter. As a result, no exchange of sodium from the tubule with hydrogen ions from the epithelial cell can be guaranteed. A reaction of the hydrogen ions with bicarbonate and thus the resorption of bicarbonate is therefore not possible.
Another reason for type I acidosis can be a defect in the sodium bicarbonate cotransporter. Here the bicarbonate is already stored in the epithelial cell, but cannot escape from it into the bloodstream. Type II acidosis is also caused by defective transport channels. However, the location of the defect is in the proximal rather than the distal tubule.
Symptoms, Ailments & Signs
In type IV acidosis, the aldosterone within the cell cannot ensure increased sodium absorption. A defective sodium-hydrogen antiporter is also often responsible for this. By blocking and flushing out sodium, not enough water can be absorbed.
The result is dehydration, hyperaldosteronism and other symptoms. The causes of defective transport channels are manifold. Other causes of renal tubular acidosis unrelated to defective transport channels and antiporters are also present.
Diagnosis & course of disease
Type I renal tubular acidosis is the most common form. It is caused by impaired secretion of hydrogen ions (H+) in the distal tubule. Hydrogen ions ensure reabsorption of bicarbonate in the distal tubule. Bicarbonate plays an important role in the body’s acid-base balance. Inadequate absorption of bicarbonate can therefore trigger acidosis.
The kidneys excrete more sodium and potassium due to poor reabsorption. The urine is only insufficiently acidified and at most reaches a pH value that is greater than or equal to six (urine pH > 6). As a result, metabolic acidosis occurs, which cannot be compensated for by the body because of the progressive deficient secretion of hydrogen ions.
The flushing out of sodium and potassium causes further clinical pictures. Hypokalemia can result from low potassium levels. Inadequate absorption of sodium leads to volume depletion of the blood and promotes hyperaldosteronism and hypercalciuria. Chronic courses of renal tubular acidosis type I are often associated with kidney stones (nephrolithiasis) or nephrocalcinosis.
The complications of renal tubular acidosis depend on the type of acidosis. Hyperaldosteronism and hypokalemia are the main features of renal tubular acidosis type I. Depending on the severity, hypokalemia can lead to severe cardiac arrhythmias, including atrial fibrillation, ventricular fibrillation and even cardiac arrest. Symptoms of paralysis appear on the muscles.
Another complication of renal tubular acidosis type I is the formation of kidney stones. These can lead to renal colic and urinary retention. Urinary retention often causes kidney damage with pelvic inflammatory disease and uremia. In uremia, substances that are excreted in the urine accumulate in the blood. In the worst case, pathological changes occur in the brain, which are often associated with disturbances of consciousness and even coma. Type II renal tubular acidosis often leads to osteoporosis and bone softening.
Here the risk of fractures and deformation of the bones is increased. In addition, growth disorders and rickety changes occur in children. Kidney stones are not usually formed. Type III renal tubular acidosis is a mixed form of types I and II. All the complications of these two types can occur here.
Finally, type IV renal tubular acidosis is characterized by hyperkalemia, which can become life-threatening if left untreated. Serious cardiac arrhythmia can occur. Cardiac arrest is sometimes the only symptom that occurs with hyperkalemia.
When should you go to the doctor?
Renal tubular acidosis should not remain untreated. Whether congenital or acquired, renal acid excretion is disrupted. If this disorder is not treated, the acidosis becomes metabolic. This conclusion applies to all forms of renal tubular acidosis, i.e. types I-IV.
Damage to the renal tubules prevents enough acid from being filtered out of the blood. The excessive acid concentration in the blood can be measured. You have to find a balance, otherwise the acid-base balance will be disturbed. The effects can be found, for example, in weakened muscles or in a reduced reflex. The electrolyte balance is increasingly disturbed.
Renal tubular acidosis can occur as a hereditary disease in children. However, they can also occur as a temporary consequence of other diseases. Autoimmune diseases or diabetes mellitus, for example, come into question. The prescription of certain medications can also lead to this. If triggered by a drug, it may need to be replaced.
The question is whether renal tubular acidosis is noticeable at all. Doctor visits are often omitted when renal tubular acidosis leads to side effects such as low or high blood potassium levels, dehydration or kidney stones. Even painful softening of the bones does not necessarily indicate renal tubular acidosis. Nevertheless, renal tubular acidosis should be considered with such symptoms.
Treatment & Therapy
By administering sodium bicarbonate and citrates, an improvement in the condition can be observed quickly. An administration of potassium is also advisable in the case of an associated low potassium balance. Type II renal tubular acidosis is characterized by a persistent resorption defect in the proximal tubule.
In type II acidosis too little bicarbonate is resorbed. However, the resorption defect does not exist in the distal tubule. Due to the different location of the defect, the uric acidification in the distal tubule remains intact. The hyperacidity, which is initiated by the lack of bicarbonate, also occurs in type II acidosis, but additional valences can be excreted by the intact functions of the distal tubule.
The subsequent symptoms of renal tubular acidosis type II are very similar to those of acidosis type I, despite the possibility of removing the excess acid. High sodium and potassium depletion is associated with volume depletion and hyperaldosteronism. Symptoms such as nephrocalcinosis and nephrolithiasis are not present in type II acidosis. Large doses of sodium citrate or sodium lactate can provide rapid relief.
Type IV renal tubular acidosis is caused by insufficient sodium absorption in the distal tubule. The defective resorption is caused by an aldosterone deficiency or aldosterone resistance. Type IV acidosis triggers hyperkalemia. However, the acidification of the urine is not affected and works perfectly. Severe hyperkalemia can be avoided with a low-potassium diet.
In order to prevent secondary diseases such as kidney stones or osteoporosis, it is very important, even after successfully treated renal tubular acidosis, to recognize recurring deficiencies and a deterioration in kidney function at an early stage. For this it is elementary to carry out regular checks of the potassium, sodium and kidney values in the blood, as well as regular pH tests of the urine with administration of ammonium chloride by the attending physician.
The follow-up treatment and the limit values depend on the type of renal tubular acidosis. If type 1 distal renal tubular acidosis is present, it is necessary to take potassium as a dietary supplement for life and, if the values deteriorate, to give additional infusions with potassium in order to prevent a new outbreak of acidosis and the development of secondary diseases. Type 2 proximal renal tubular acidosis requires lifelong sodium supplementation.
If the values in the blood deteriorate, additional infusions may also be necessary here to prevent the acidosis from breaking out again and the development of secondary diseases. If type 3 renal tubular acidosis is present, type 1 and type 2 treatment must be combined. In the case of type 4 renal tubular acidosis, on the other hand, a low-potassium diet must be adhered to for life because of the possibility of potassium poisoning.
You can do that yourself
Renal tubular acidosis is easy to cope with in everyday life. When the first symptoms appear, it is important to have them clarified by a doctor at an early stage. In this way, severe electrolyte imbalances can be avoided.
In renal tubular acidosis type I, sodium bicarbonate should be drunk daily. To prevent the risk of hypokalemia, potassium levels can be influenced by diet. Eating foods rich in potassium is recommended. These are, for example, nuts, yeast, dried fruit, bananas, tomatoes, mushrooms, cocoa and chocolate or herbs.
In renal tubular acidosis type IV, on the other hand, a low-potassium diet should be aimed at. Avoiding high-potassium foods and increasing the consumption of low-potassium foods can lower the potassium balance in a simple and everyday way. Foods such as rice, semolina, tofu, lemons or dairy products are naturally low in potassium. The preparation of food can also have an influence on the potassium content. Potatoes should be gently cooked at 70 degrees and slowly cooled. The cooking water should not be consumed. In this way, up to 80 percent of potassium can be reduced. In principle, it is advisable to boil other foods as well in order to reduce the potassium concentration they contain. In addition, tea should be drunk instead of coffee – tea contains significantly less potassium.