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Renal tubular acidosis - distal
Definition A condition in which the body is in an acidic state, caused by abnormal excretion of acid (hydrogen ions) from the distal tubule of the kidney.
Alternative Names Distal renal tubular acidosis; Renal tubular acidosis type I; Type I RTA; RTA - distal; Classical RTA
Causes, incidence, and risk factors NORMAL ACID-BASE REGULATION An ion is a substance that can carry an electrical charge. The acid-base balance is defined by the concentration of hydrogen ions (the pH). The normal pH of the body is very slightly alkaline. Acidic substances in the body include carbon dioxide and molecules containing hydrogen ions. These are buffered (counteracted) by alkaline substances, primarily bicarbonate, with some buffering by phosphate, proteins , hemoglobin , and other substances. Increased carbon dioxide or decreased bicarbonate levels can create an acidic state in the body, called acidosis . Decreased carbon dioxide or increased bicarbonate levels can create an excess alkaline state, called alkalosis . If the defect is caused by changes in carbon dioxide levels, it is a respiratory acidosis or respiratory alkalosis . If the defect is caused by changes in bicarbonate levels, it is a metabolic acidosis or metabolic alkalosis. The respiratory system regulates the levels of carbon dioxide through changes in the breathing rate. Carbon dioxide is lost with faster breathing and increased when breathing slows. This provides fast, but temporary regulation of body pH. The major, long-term regulation of body pH occurs in the kidneys, which excrete acids, and excrete or create bicarbonate for use in the body. DISTAL RENAL TUBULAR ACIDOSIS Renal tubular acidosis is one common cause of metabolic acidosis. Distal renal tubular acidosis (Type I RTA) is a disorder caused by a defect in the secretion of hydrogen ions in the distal renal tubule (the late portion of the kidney tubule). This causes a reduction in the reabsorption of bicarbonate into the bloodstream. Type I RTA is caused by a variety of conditions including hereditary disorders, autoimmune diseases and certain drugs including amphotericin B, lithium, and analgesics. Renal tubular acidosis causes disorders of the body related to the loss of bicarbonate and inability to excrete hydrogen. The body attempts to maintain an electro-chemical balance between positively charged and negatively charged molecules. If the excretion of a molecule is abnormal, the excretion of other molecules may become abnormal in an attempt to maintain a balance. Type I RTA causes retention of acid and is also associated with mild loss of potassium in the urine. The acidic condition of the body causes calcium to dissolve from the bones. The calcium accumulates in the bloodstream, and excess serum calcium is excreted by the kidneys, causing a loss of total body calcium and resulting in osteomalacia or rickets , impaired growth of children, skeletal deformities, and muscle weakness . There is an increased incidence of kidney stones and nephrocalcinosis associated with the excessive excretion of calcium and phosphate through the kidneys.
  • fatigue
  • weakness
  • confusion
  • or
  • decreased alertness
  • increased rate of breathing
  • Signs and tests
  • The most common presentation is with
  • kidney stones ( renal calculi ). The respiratory rate may be rapid as the body attempts to decrease carbon dioxide in response to decreased bicarbonate levels. Signs and symptoms of osteomalacia or rickets , nephrocalcinosis , or electrolyte disturbances may appear.
  • The simultaneous measurements of the blood pH and the
  • urine pH may show inadequate hydrogen ion excretion.
  • A
  • urinalysis may show abnormalities including increased levels of calcium and potassium in the urine. The urine pH is usually > 5.0.
  • An ABG (
  • arterial blood gas ) and blood chemistries may indicate metabolic acidosis and hypokalemia (a low blood-potassium level).
    Treatment The goal of treatment is to restore the normal pH (acid-base level) and normal electrolyte balance. This will indirectly correct bone disorders and reduce the risk of nephrocalcinosis and kidney stones . The underlying cause should be corrected if it can be identified. Alkaline medications such as potassium citrate and sodium bicarbonate are administered to correct the acidic condition of the body. Sodium bicarbonate administration may correct the loss of potassium and calcium. Vitamin D and calcium supplements are usually not given because the tendency toward nephrocalcinosis persists even after bicarbonate therapy.
    Support Groups 
    Expectations (prognosis) The disorder must be treated to reduce its effects and complications, which can be permanent and/or life-threatening. Most cases resolve successfully with treatment.
  • osteomalacia
  • rickets
  • nephrocalcinosis
  • kidney stones
  • electrolyte
  • disturbances including (but not limited to)
  • hypokalemia
    Calling your health care provider Call your health care provider if symptoms indicate distal renal tubular acidosis may be present. Call your health care provider if new symptoms develop, including bone pain , pain in the back or flank or abdomen, skeletal deformities, increased heart rate or irregular heartbeat , muscle cramps , decreased urine output , bloody urine , or other symptoms. Severe decrease in alertness or orientation , decreased consciousness , and seizures , are emergency symptoms that can develop.
    Prevention There is no prevention for this disorder.