Renal Tubular Acidosis

Overview

Renal tubular acidosis (RTA) is a condition in which the kidneys fail to properly handle acid. The kidneys normally remove excess acid from the blood and pass it into the urine, helping keep the body's acid-base balance steady. In RTA, the small tubes (tubules) inside the kidneys do not do this job correctly, so acid builds up in the blood, a state called metabolic acidosis.

There are several types, most commonly called type 1, type 2, and type 4, each involving a different part of the tubules and a different mechanism. RTA can be present from birth or develop later from diseases or medications. Left untreated, it can affect growth, bone health, kidney stones, and electrolyte balance, but it is usually manageable once diagnosed.

Symptoms

Symptoms vary by type and severity, and some people have few or no symptoms, with the condition discovered through routine blood tests. When symptoms occur, they may include:

• Fatigue and weakness, sometimes from low potassium.
• Muscle weakness or cramps.
• Increased thirst and urination.
• Bone pain or softening, and a higher risk of fractures over time.
• Kidney stones or deposits of calcium in the kidneys, especially in one type.
• In children, poor growth and failure to gain weight as expected.
• Confusion or, in severe acidosis, more serious symptoms.

Because the symptoms can be vague, RTA is often found when blood or urine tests show an acid imbalance.

Causes

RTA results from problems in the kidney tubules. Causes differ by type:

• Inherited forms present from birth, caused by genetic differences affecting the tubules.
• Autoimmune diseases, which can damage the tubules.
• Certain medications and toxins that affect kidney function.
• Other kidney diseases and conditions that affect the tubules.
• Problems with the hormone aldosterone or how the kidney responds to it, which underlie one type.

In some cases no clear cause is found, while in others RTA is linked to a broader medical condition.

Risk Factors

Factors that can increase the risk of RTA include:

• A family history of an inherited form.
• Autoimmune conditions affecting the kidneys.
• Other forms of chronic kidney disease.
• Use of certain medications that can affect the tubules.
• Diabetes, which is associated with one type of RTA.
• Conditions that disturb the body's mineral and acid balance.

Diagnosis

Diagnosis involves confirming that acid is building up in the blood and then identifying which type of RTA is present, since the types are treated somewhat differently. Evaluation may include:

• Blood tests showing metabolic acidosis, along with measurement of potassium, bicarbonate, and other electrolytes and kidney function.
• Urine tests to measure how acidic the urine is and to assess how the kidneys are handling acid.
• Specialized tests that challenge the kidney's ability to acidify urine, which help distinguish the types.
• Imaging such as ultrasound to check for kidney stones or calcium deposits.
• Additional tests to look for an underlying cause, such as an autoimmune disease.

Treatment

Treatment aims to correct the acid imbalance, restore electrolyte balance, and prevent complications:

• Alkali therapy, such as oral sodium bicarbonate or sodium or potassium citrate, to neutralize excess acid in the blood.
• Potassium supplements when potassium is low, as in some types.
• Medications or adjustments to manage potassium when it is high, as in another type.
• Treating the underlying cause, such as adjusting a medication or managing an autoimmune disease.
• Measures to prevent and treat kidney stones and to protect bone health.

In children, prompt treatment is important to support normal growth and bone development, since untreated acidosis can interfere with both. The right dose of alkali and supplements is adjusted over time based on blood and urine tests, and treatment is often continued long term. Many people do well with ongoing therapy and regular monitoring, and complications such as bone disease and kidney stones can often be prevented when the acid imbalance is kept under control.

Prevention

Inherited forms cannot be prevented, but some steps can reduce risk or limit complications:

• Managing underlying conditions such as autoimmune diseases and diabetes.
• Reviewing medications with a doctor when kidney effects are a concern.
• Staying well hydrated and following treatment to reduce the risk of kidney stones.
• Keeping regular follow-up appointments and lab tests to catch imbalances early.

When to See a Doctor

See a doctor if you have persistent fatigue, muscle weakness, bone pain, recurrent kidney stones, or if a child is not growing as expected, since these can be signs of an acid or electrolyte imbalance that needs testing.

Seek urgent care for severe muscle weakness, an irregular heartbeat, confusion, or severe symptoms, as marked acidosis or potassium imbalance can be dangerous and may require prompt treatment.

Related Topics

Frequently Asked Questions

References

1. MedlinePlus, U.S. National Library of Medicine.
2. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
3. Mayo Clinic.