Proximal renal tubular acidosis

Definition

Proximal renal tubular acidosis is a condition that occurs when the kidneys don't properly remove acids in the urine, leaving the blood too acidic.

Alternative Names

Renal tubular acidosis - proximal; Type II RTA; RTA - proximal; Renal tubular acidosis type II

Causes, incidence, and risk factors

Your kidneys help regulate your body's acid-base balance (pH). Acidic substances in the body are buffered (counteracted) by alkaline substances, primarily bicarbonate.

The kidneys contain more than a million filtering units, called nephrons. Bicarbonate is reabsorbed into the blood in the initial (proximal) part of the tubule of each nephron. Proximal renal tubular acidosis (Type II RTA) occurs when bicarbonate is not properly reabsorbed by the proximal tubules, leaving the body in an acidic state (called acidosis).

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

Causes of type II RTA include:

• Cystinosis
• Drugs such as ifosfamide (a chemotherapy drug), outdated tetracycline, aminoglycoside antibiotics, or acetazolamide
• Fanconi Syndrome
• Inherited fructose intolerance
• Multiple myeloma
• Primary hyperparathyroidism
• Sjogren syndrome
• Wilson's disease

Symptoms

• Confusion or decreased alertness
• Dehydration
• Fatigue
• Increased breathing rate
• Osteomalacia
• Muscle pain
• Rickets
• Weakness

Other symptoms can include:

• Decreased urine output
• Increased heart rate or irregular heartbeat
• Muscle cramps
• Pain in the bones, back, flank, or abdomen
• Skeletal deformities

Signs and tests

Arterial blood gas and blood chemistries may suggest metabolic acidosis and electrolyte imbalances, most often low levels of potassium or bicarbonate.

Other tests that may be done include:

• Blood pH level
• Urine pH
• Urinalysis may show abnormal levels of phosphate, calcium, glucose, and amino acids

• Acid loading test (pH)
• Blood potassium level
• Urine calcium
• Urine citric acid
• Urine potassium level

Treatment

The goal is to restore the normal pH (acid-base level) and 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 acid-induced bone disease such as rickets, and to allow normal growth. The underlying cause should be corrected if it can be found.

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

Vitamin D and calcium supplements may be needed to help reduce skeletal deformities resulting from osteomalacia or rickets.

Expectations (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.

Complications

• Electrolyte imbalances, such as hypokalemia
• Osteomalacia
• Rickets

Calling your health care provider

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

Get medical help immediately if you develop any of the following emergency symptoms:

• Decreased alertness or orientation
• Decreased consciousness
• Seizures

Prevention

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

References

Seifter JL. Acid-base disorders. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 119.