RTA (for its acronym in English), is a disease that occurs when the kidneys do not excrete acids in the urine, which causes the person’s blood to remain too acidic.
Without proper treatment, chronic acidity of the blood causes growth retardation, kidney stones, bone disease, chronic kidney disease, and possibly total kidney failure.
Cells in the body use chemical reactions to carry out tasks like converting food into energy and repairing tissues.
These chemical reactions generate acids. A little acid in the blood is normal, but too much acid acidosis can disrupt many bodily functions.
Healthy kidneys help maintain acid-base balance by excreting acids in the urine and returning bicarbonate (an alkaline or basic substance) to the blood. This “regenerated” bicarbonate neutralizes much of the acid that is created when food breaks down in the body.
The movement of substances such as bicarbonate between the blood and kidney structures is called transport.
How is renal tubular acidosis diagnosed?
To diagnose RTA, doctors check the acid-base balance in blood and urine samples. If the blood is more acidic than it should be and the urine is less acidic than it should be, the RTA may be the reason, but additional information is needed to rule out other causes.
If RTA is the reason, additional information about urine sodium, potassium, and chloride levels and blood potassium level will help identify what type of RTA a person has.
In all cases, the first goal of therapy is to neutralize acid in the blood, but different treatments may be needed to address the different underlying causes of acidosis.
What are the types, causes, and symptoms of RTA?
Type 1: Classical distal RTA
Type 1 is also called classic distal RTA. “Distal,” meaning distant, refers to the point in the kidney’s urine-forming tube where the defect occurs, relatively distant from the point where blood fluid enters the small tube, or tubule, that collects fluid and waste for urine form
This disorder can be inherited as a primary disorder or it can be a symptom of a disease that affects many parts of the body. Researchers have discovered abnormal genes responsible for inherited forms of the disease.
More often, however, classic distal ACR occurs as a result of systemic diseases, diseases that affect many organ systems, such as autoimmune diseases, Sjögren’s syndrome, and lupus, which also attack the distal tubule.
Other diseases and conditions associated with classic distal ACR include:
- Anemia drepanocítica.
- Hyperparathyroidism .
- Active chronic hepatitis.
- Primary biliary cirrhosis.
- An inherited form of deafness.
- Analgesic nephropathy.
- Rejection of a transplanted kidney.
- Renal medullary cystic disease.
- Obstructive uropathy.
- Chronic urinary tract infections.
Many of these conditions cause abnormal calcium deposits to build up in the kidney and affect the function of the distal tubule.
An important consequence of classic distal ACR is a low level of potassium in the blood. The level drops if the kidneys excrete too much potassium in the urine instead of returning it to the blood supply.
Because potassium helps regulate nerve and muscle health and heart rate, low levels can cause in some cases:
- Extreme weakness
- Irregular heartbeat
Untreated classic distal ACR causes growth retardation in children and progressive kidney and bone disease in adults. Restoring normal growth and preventing kidney stones are the main goals of therapy.
If acidosis is corrected with sodium bicarbonate or sodium citrate, low potassium levels, salt depletion, and calcium in the urine will be corrected. This alkaline therapy also helps slow the development of kidney stones and stabilizes kidney function, so kidney failure does not progress.
Babies may need potassium supplements, but older children and adults rarely do so because alkaline therapy prevents the kidney from excreting potassium in the urine.
Type 2: proximal RTA
Type 2 is also called proximal RTA. The word “proximal,” meaning close, indicates that the defect is closer to the point where fluid and debris from the blood enter the tubule.
This form of RTA occurs most often in children as part of a disorder called Fanconi syndrome.
Features of Fanconi syndrome include abnormal excretion of:
- Amino acids.
- Phosphate to urine.
- Vitamin D deficiency.
- Low level of potassium in the blood.
Proximal ACR can also be the result of inherited disorders that disrupt the body’s normal breakdown and use of nutrients.
Examples include the rare disease cystinosis, in which cystine crystals are deposited in bone and other tissues; hereditary fructose intolerance; and Wilson’s disease.
Proximal RTA also occurs in patients treated with ifosfamide, a drug used in chemotherapy.
Some older drugs, such as acetazolamide or obsolete tetracycline, can also cause a proximal RTA. In adults, proximal RTA can complicate conditions such as multiple myeloma, or it can occur in people who experience chronic rejection of a transplanted kidney.
When possible, identifying and correcting underlying causes are important steps in treating acquired forms of proximal RTA.
Diagnosis is based on chemical analysis of blood and urine samples. Children with this disorder would likely receive large doses of an oral alkali, such as sodium bicarbonate or potassium citrate, to treat acidosis and prevent bone disorders, kidney stones, and growth failure.
Correction of acidosis and low potassium levels restore normal growth patterns, allowing bones to mature while preventing further kidney disease. Vitamin D supplements may also be necessary to help prevent bone problems.
Type 3 is rarely used as a classification because it is now thought to be a combination of type 1 and type 2.
Type 4: hyperkalemia RTA
Type 4 is also called hyperkalemic RTA and is caused by a generalized transport abnormality of the distal tubule.
The transport of electrolytes such as sodium, chloride, and potassium that normally occurs in the distal tubule is impaired. This form is distinguished from classic distal RTA and proximal RTA because it results in elevated potassium levels in the blood rather than low levels.
Or, low potassium hypokalemia or high potassium hyperkalemia can be a problem because potassium is important for regulating your heart rate.
RTA type 4 occurs when blood levels of the hormone aldosterone are low or when the kidneys do not respond to it.
Aldosterone directs the kidneys to regulate sodium, potassium, and chloride levels in the blood. Type 4 RTA also occurs when the tubular transport of electrolytes such as sodium, chloride, and potassium is impaired due to an inherited disorder or the use of certain medications.
Medications that can cause type 4 RTA include:
- Diuretics used to treat congestive heart failure such as spironolactone or eplerenone.
- Blood pressure medications called angiotensin converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs).
- The antibiotic trimethoprim.
- The antibiotic pentamidine, which is used to treat pneumonia.
- An agent called heparin that prevents blood from clotting.
- A class of pain relievers called non-steroidal anti-inflammatory drugs (NSAIDs).
- Some immunosuppressive medications used to prevent rejection.
Type 4 RTA can also be the result of diseases that alter the structure and function of the kidney. These diseases can be:
- Diabetic nephropathy.
- VIH / PAGE.
- Addison’s disease.
- Sickle cell disease
- Urinary tract obstruction.
- Removal or destruction of both adrenal glands.
- Renal transplant rejection.
For people who make aldosterone but cannot use it, researchers have identified the genetic basis for their body’s resistance to the hormone. To successfully treat RTA type 4, patients may need alkaline agents to correct acidosis and medication to lower potassium in the blood.
If treated early, most people with any type of RTA will not develop permanent kidney failure. Therefore, the goal is early recognition and appropriate therapy, which should be maintained and monitored throughout the person’s life.
What is the treatment for renal tubular acidosis?
- Stop the medicine, which may have caused the renal tubular acidosis.
- Treat autoimmune disease with high doses of corticosteroids or cyclophosphamides.
- Treat primary hyperparathyroidism.
- Another form of treatment for renal tubular acidosis can be alkaline medications to restore the acid-base balance in the blood, such as sodium bicarbonate, which helps reduce the acid concentration in the blood.
- Oral bicarbonate supplement : the amount of bicarbonate prescribed depends on blood and biological levels, thiazide diuretics retain bicarbonate and correct acidosis.
- Renal tubular acidosis (RTA) is a disease that occurs when the kidneys do not excrete acids in the urine, causing the person’s blood to remain too acidic.
- Without proper treatment, chronic acidity of the blood causes growth retardation, kidney stones, bone disease, chronic kidney disease, and possibly total kidney failure.
- If RTA is suspected, additional information about urine sodium, potassium, and chloride levels and blood potassium level will help identify what type of RTA a person has.
- In all cases, the first goal of therapy is to neutralize acid in the blood, but different treatments may be needed to address the different underlying causes of acidosis.