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Renal Tubular Acidosis

(RTA)

By James I. McMillan, MD

In renal tubular acidosis, the kidney tubules malfunction, resulting in excess levels of acid in the blood.

  • The tubules of the kidneys that remove acid from the blood are damaged when a person takes certain drugs or has another disorder that affects the kidneys.

  • Often muscle weakness and diminished reflexes occur when the disorder has been present for a long time.

  • Blood tests show high acid levels and a disturbance of the body's acid-base balance.

  • Some people drink a solution of baking soda every day to neutralize the acid.

To function normally, body acids and alkali (such as bicarbonate) must be balanced. Normally, the breakdown of food produces acids that circulate in the blood. The kidneys remove acids from the blood and excrete them in the urine. This function is predominantly carried out by the kidney tubules. In renal tubular acidosis, the kidney tubules malfunction in one of two ways that tend to increase acids in the blood ( metabolic acidosis):

  • Too little of the acids the body produces are excreted, so acid levels in blood increase.

  • Too little of the bicarbonate that filters through the kidney tubules is reabsorbed, so too much bicarbonate is lost in the urine.

In renal tubular acidosis, the balance of electrolytes is also affected. Renal tubular acidosis may lead to the following problems:

  • Low or high potassium levels in the blood

  • Calcium deposits in the kidneys, which may lead to kidney stones

  • Painful softening and bending of the bones (osteomalacia or rickets)

Renal tubular acidosis may be a permanent, inherited disorder in children. However, it may be an intermittent problem in people who have other disorders, such as diabetes mellitus, sickle cell disease, or an autoimmune disorder (such as systemic lupus erythematosus [lupus]). Renal tubular acidosis may also be a temporary condition brought on by blockage of the urinary tract or by drugs, such as acetazolamide, amphotericin B, angiotensin-converting enzyme (ACE) inhibitors, angiotensin II receptor blockers (ARBs), and diuretics that conserve the body’s potassium (so-called potassium-sparing diuretics).

If renal tubular acidosis persists, it may damage the kidney tubules and progress to chronic kidney disease.

There are four types of renal tubular acidosis, types 1 through 4. The types are distinguished by the particular abnormality in kidney function that causes acidosis. All four types are uncommon, but type 4 is the most common and type 3 is extremely rare.

Some Types of Renal Tubular Acidosis

Type

Cause

Underlying Abnormality

Resulting Symptoms and Metabolic Abnormalities

1

May be hereditary or may be triggered by an autoimmune disorder or certain drugs

Cause usually not known, especially in women

Inability to excrete acid into the urine

High blood acidity

Mild dehydration

Low potassium levels in the blood, leading to muscle weakness and paralysis

Fragile bones

Bone pain

Calcium deposits, leading to kidney stones

Chronic kidney disease

2

Usually caused by a hereditary disease such as Fanconi syndrome, hereditary fructose intolerance, Wilson disease, or oculocerebrorenal syndrome (Lowe syndrome)

May also be caused by multiple myeloma, heavy metal poisoning, or certain drugs

Inability to reabsorb bicarbonate from the urine, so too much bicarbonate is excreted

High blood acidity

Fragile bones

Bone pain

Mild dehydration

Low potassium levels in the blood

Decreased production of the active form of vitamin D

4

Not hereditary

Caused by diabetes, an autoimmune disorder, chronic kidney disease, or an obstruction in the urinary tract

Worsened by certain drugs, including potassium-sparing diuretics, angiotensin-converting enzyme inhibitors, and angiotensin II receptor blockers

Deficiency of or inability to respond to aldosterone, a hormone that helps regulate potassium and sodium excretion by the kidneys

Mildly increased blood acidity and high potassium levels in the blood that rarely cause symptoms, unless the potassium level is unusually high (in that case, irregular heartbeats and muscle paralysis develop)

Note: Type 3 is a mixture of Types 1 and 2 and is extremely rare.

Symptoms

Many people have no symptoms. Most others develop symptoms only after the disorder has been present for a long time. Which symptoms eventually develop depend on the type of renal tubular acidosis.

Types 1 and 2

When potassium levels in the blood are low, as occurs in types 1 and 2, neurologic problems may develop, including muscle weakness, diminished reflexes, and even paralysis. In type 1, kidney stones may develop, causing damage to kidney cells and, in some cases, chronic kidney disease. In type 2 and sometimes in type 1, bone pain and osteomalacia may occur in adults and rickets may occur in children.

Type 4

In type 4, potassium levels typically increase, although it is uncommon for the level to rise high enough to cause symptoms. If the level becomes too high, irregular heartbeats and muscle paralysis may develop.

Diagnosis

  • Blood tests

  • Urine tests

A doctor considers the diagnosis of type 1 or type 2 renal tubular acidosis when a person has certain characteristic symptoms (such as muscle weakness and diminished reflexes) and when tests reveal high levels of acid and low levels of bicarbonate and potassium in the blood.

Type 4 renal tubular acidosis is usually suspected when high potassium levels accompany high acid levels and low bicarbonate levels in the blood. Tests on urine samples and other tests help to determine the type of renal tubular acidosis.

Treatment

  • Drinking sodium bicarbonate daily

Treatment depends on the type.

Types 1 and 2

Types 1 and 2 are treated by drinking a solution of sodium bicarbonate (baking soda) every day to neutralize the acid that is produced from food. This treatment relieves the symptoms and prevents kidney failure and bone disease or keeps these problems from becoming worse. Other specially prepared solutions are available, and potassium supplements may also be required.

Type 4

In type 4, the acidosis is so mild that bicarbonate may not be needed. High potassium levels in the blood can usually be kept in check by restricting potassium intake, avoiding dehydration, using diuretics that increase potassium loss, and substituting different drugs or adjusting drug dosages.

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