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Renal Tubular Acidosis

A syndrome of persistent dehydration, hyperchloremia, hypokalemia, metabolic acidosis, and nephrocalcinosis, renal tubular acidosis (RTA) results from the kidneys' inability to conserve bicarbonate. This disorder occurs as distal RTA (Type I, or classic RTA) or proximal RTA (Type II). The prognosis is usually good but depends on the severity of renal damage that precedes treatment.

Causes

The kidneys normally remove substances such as acid from the blood and excrete them through the urine. There are three types of renal tubular acidosis, called Types 1, 2, and 4 (there is no Type 3). Type 1 may be hereditary or can be triggered by an autoimmune disease (such as lupus), certain drugs, chronic kidney obstruction, or kidney transplant. Type 2 is usually caused by a hereditary disease, such as hereditary fructose intolerance, Lowe's syndrome, Wilson's disease, or Fanconi's syndrome; heavy metal poisoning; kidney transplant; vitamin D deficiency; and certain drugs. Type 4 is the only type that is not hereditary, but is caused by autoimmune disease, diabetes mellitis, urinary tract obstruction, or sickle cell disease.

Signs and symptoms

In infants, RTA produces anorexia, vomiting, occasional fever, polyuria, dehydration, growth retardation, apathy, weakness, tissue wasting, constipation, nephrocalcinosis, and rickets.

In children and adults, RTA may lead to urinary tract infection, rickets, and growth problems. Possible complications of RTA include nephrocalcinosis and pyelonephritis.

Diagnosis

To diagnose RTA, your doctor will check the acid-base balance in samples of your blood and urine. If the blood is more acidic than it should be and the urine less acidic than it should be, RTA may be the reason, but additional information is needed first to rule out other causes. If RTA is suspected, additional information about the sodium, potassium, and chloride levels in the urine and the potassium level in the blood will help identify which of the three types of RTA you have. 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.

Treatment

Supportive treatment for patients with RTA requires replacement of those substances being abnormally excreted, especially bicarbonate. It may include sodium bicarbonate tablets or Shohl's solution to control acidosis, oral potassium for dangerously low potassium levels, and vitamin D for bone disease. If pyelonephritis occurs, treatment may include antibiotics as well.

Treatment for renal calculi secondary to nephrocalcinosis varies and may include supportive therapy until the calculi pass or until surgery for severe obstruction is performed.

Prevention

Most of the disorders that cause proximal renal tubular acidosis are not preventable.