Proximal renal tubular acidosis

Definition

The term "renal" refers to the kidney. The kidney contains over a million functional units called nephrons, which filter your blood and produce urine. Normally, a blood buffer called bicarbonate is reabsorbed into the blood in the proximal tubule of each nephron. When it is not reabsorbed properly, your body is left an acidic state (called acidosis).

Alternative Names

Causes

When healthy, your body is very slightly alkaline. Acidic substances in the body, such as carbon dioxide, are buffered (counteracted) by alkaline substances, primarily bicarbonate. Your kidneys regulate your body's pH by controlling acids and bicarbonate buffer.

An acidic state in your body can be caused by high carbon dioxide levels (respiratory acidosis). It can also be caused by low bicarbonate levels (metabolic acidosis).

Proximal renal tubular acidosis (Type II RTA) is a result of poor bicarbonate reabsorption by the proximal tubules. This leads to lower bicarbonate buffer in the blood, causing metabolic acidosis.

Type II RTA is less common than  Type I RTA. It most commonly occurs during infancy, and may go away by itself.

Many different molecular abnormalities can lead to Type II RTA. It can occur in an isolated form or with general problems with the proximal tubule. (See Fanconi's Syndrome.

People with Type II RTA tend to reabsorb chloride to compensate, and thus have high blood serum chloride levels. They are also low in potassium.

Symptoms

• fatigue
• weakness
• confusion or decreased alertness
• increased rate of breathing
• muscle pain

Exams and Tests

• Your breathing rate may be rapid as your body attempts to decrease carbon dioxide.
• You may have symptoms of osteomalacia and rickets.
• You may be dehydrated from loss of water into the urine (low potassium levels interfere with the kidney's ability to concentrate the urine).
• Measurements of the blood pH and urine pH may show a problem. The urine may be alkaline, although this may change as the body becomes more acidic.
• A urinalysis may show abnormal levels of phosphate, calcium, glucose, and amino acids in the urine.
• Arterial blood gases and blood chemistries may indicate metabolic acidosis and electrolyte abnormalities.

• urine potassium level (high)
• blood potassium level (low)
• urine citric acid
• urine calcium
• acid loading test (pH)

Treatment

The goal is to restore the normal pH (acid-base level) and a normal electrolyte balance to the body. This will indirectly correct bone disorders and reduce the risk of osteomalacia and osteopenia in adults.

Some adults may need no treatment. All children need alkaline medication to prevent bone disease (rickets in particular) and to permit normal growth. The underlying cause should be corrected if it can be identified.

Alkaline medications include sodium bicarbonate and potassium citrate. They correct the acidic condition of the body and correct low potassium levels. Thiazide diuretics may indirectly decrease bicarbonate loss but may exacerbate the low potassium levels.

Vitamin D and calcium supplements may be needed to aid in the reduction of skeletal deformities resulting from osteomalacia or rickets.

Outlook (Prognosis)

Although the underlying cause of proximal renal tubular acidosis may go away by itself, the effects and complications can be permanent or life-threatening. Treatment is usually successful.

Possible Complications

• osteomalacia
• rickets
• electrolyte disturbances, such as hypokalemia

When to Contact a Medical Professional

Call your health care provider if you have symptoms of proximal renal tubular acidosis.

Call your health care provider if new symptoms develop, including pain in the bones, back, flank, or abdomen; skeletal deformities, increased heart rate or irregular heartbeat, muscle cramps, decreased urine output, bloody urine, or other symptoms.

Get medical help immediately if decreased alertness or orientation, decreased consciousness, or seizures develop.

Prevention

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