Distal renal tubular acidosis (dRTA) is a kidney condition that disrupts the body’s acid-base balance. It occurs when the kidneys struggle to adequately remove acids from the blood, leading to an accumulation of acid in the bloodstream. This imbalance can affect various bodily functions and may vary in severity.
Understanding Distal Renal Tubular Acidosis
The kidneys play a complex role in maintaining the body’s internal balance, including regulating acid and base levels. Specifically, the distal tubules, a particular section of the kidney’s filtering units, are responsible for secreting hydrogen ions (acid) into the urine and reabsorbing bicarbonate (a base) back into the bloodstream. This process helps to keep the blood’s pH within a healthy range, typically between 7.35 and 7.45.
In dRTA, the alpha intercalated cells within the distal tubules, which are responsible for acid secretion, do not function correctly. This impairment means that the kidneys cannot effectively excrete the daily acid load produced by the body, such as from normal metabolic processes or a protein-rich diet. The resulting buildup of acid in the blood is known as metabolic acidosis.
Causes of Distal Renal Tubular Acidosis
Distal renal tubular acidosis can stem from various factors, broadly categorized into inherited (primary) and acquired (secondary) forms. Primary dRTA often has a genetic basis, meaning it is passed down through families. Specific genetic mutations, such as those in the SLC4A1, ATP6V0A4, or ATP6V1B1 genes, have been linked to inherited dRTA. These genes are involved in managing the body’s acid-base balance.
Secondary dRTA develops due to underlying medical conditions or certain medications. Common causes include autoimmune diseases like Sjögren’s syndrome, systemic lupus erythematosus (lupus), and rheumatoid arthritis. Medications such as the antifungal amphotericin B, the psychiatric medication lithium, and certain antibiotics like pentamidine can also induce dRTA. Other potential causes include:
- Amyloidosis
- Fabry disease
- High blood calcium levels
- Sickle cell disease
- Wilson disease
Identifying Distal Renal Tubular Acidosis
Recognizing distal renal tubular acidosis involves observing symptoms and undergoing diagnostic tests. Individuals with dRTA may experience:
- Muscle weakness, fatigue, and bone pain
- Kidney stones, sometimes leading to flank or abdominal pain
- Impaired growth or failure to thrive in children
- Increased breathing rate
- Confusion or decreased alertness in severe cases
Diagnosis involves a physical examination, blood tests, and urine tests. Blood work measures electrolytes like sodium, potassium, and chloride, and assesses blood pH. Bicarbonate levels are also measured. Urine tests (urinalysis) check electrolyte levels and urine pH, which in dRTA is often inappropriately high (greater than 5.3 to 6.0) despite systemic acidosis. Genetic testing may be offered if an inherited form is suspected.
Treatment and Management
The primary goal of treating distal renal tubular acidosis is to restore the body’s normal acid and electrolyte balance. This is achieved through alkali therapy, administering alkaline agents to neutralize excess acid in the blood. Common agents include sodium bicarbonate, potassium bicarbonate, sodium citrate, or potassium citrate. Sodium bicarbonate is often used to lower blood acidity, while potassium citrate may be preferred if sodium bicarbonate is not effective or well-tolerated, and it also helps prevent calcium deposits in the kidneys.
Regular monitoring of blood chemistry is important to ensure appropriate dosage adjustments of alkali therapy. Correcting the acid-base imbalance also helps address other electrolyte disturbances, such as low potassium levels, which are common in dRTA. If secondary dRTA is present, addressing the underlying condition or modifying medications that contribute to the acidosis is also part of the management strategy. While specific dietary changes are not always the main treatment, a diet higher in alkali-producing fruits and vegetables and lower in acid-producing animal products may support overall acid-base balance.
Potential Complications
If distal renal tubular acidosis is left untreated or inadequately managed, several health problems can arise. One common complication is recurrent kidney stones, due to high levels of calcium in the urine and an inability to properly acidify the urine. Calcium deposits can also accumulate in the kidneys, a condition called nephrocalcinosis.
Bone disease is another complication. The body may draw calcium and other buffers from bones to neutralize excess acid, leading to osteomalacia (softening of bones in adults) or rickets (bending of bones in children). This can increase fracture risk.
Electrolyte disturbances, particularly low blood potassium (hypokalemia), are frequent, potentially causing severe muscle weakness, breathing difficulties, and abnormal heart rhythms. Prolonged or severe dRTA can lead to kidney damage and may progress to chronic kidney disease or kidney failure requiring dialysis or transplant.