ConditionKidneys & urinary tract
Renal Tubular Acidosis
Renal tubular acidosis (RTA) is a group of conditions in which the kidney tubules cannot properly remove acid from the blood or hold on to bicarbonate, even though overall kidney filtering may be normal. Acid builds up in the body (metabolic acidosis). Depending on the type, RTA can cause low or high potassium, kidney stones, weak bones, muscle weakness and poor growth in children. It may be inherited or caused by autoimmune diseases, medicines or diabetes. Treatment with alkali supplements and potassium management is usually effective.
Also called: RTA, kidney tubule acid disorder, distal RTA, proximal RTA, type 4 RTA
At a glance
- What it is
- Kidney tubules fail to excrete acid or reabsorb bicarbonate, causing a normal anion gap metabolic acidosis.
- Main types
- Type 1 (distal), type 2 (proximal), type 4 (hyperkalemic, the most common in adults).
- Causes
- Inherited gene mutations; autoimmune disease (Sjögren's, lupus); medicines; diabetes; myeloma.
- Symptoms
- Fatigue, muscle weakness, kidney stones, bone pain, poor growth in children; often found on blood tests.
- Diagnosis
- Blood gases and electrolytes, urine pH and urine anion gap.
- Treatment
- Alkali (bicarbonate or citrate), potassium supplements or potassium lowering, treating the cause.
When to get help
Call 911 or go to the ER
- Sudden severe muscle weakness or paralysis (possible very low potassium)
- Palpitations, irregular heartbeat or fainting (possible dangerous potassium levels)
- Deep, rapid breathing with confusion or extreme tiredness
See a doctor within a day or two
- Severe one-sided flank pain spreading to the groin, with blood in urine (possible kidney stone)
- Muscle cramps and weakness with abnormal potassium on a blood test
Book a routine appointment
- A child who is not growing or gaining weight normally, with vomiting or excessive urination
- Recurrent kidney stones, especially at a young age
- Bone pain or fractures with low bicarbonate on blood tests
- Dry eyes and dry mouth with kidney stones or low potassium
How the kidneys control acid
Normal metabolism produces acid every day. The kidneys keep blood pH in a narrow range by:
- reabsorbing bicarbonate (a base) in the proximal tubule
- excreting acid into the urine in the distal tubule
When either process fails, acid accumulates. Unlike kidney failure, filtration (eGFR) may be normal in RTA.
Types of renal tubular acidosis
| Type | Problem | Potassium | Urine pH | Key complications |
|---|---|---|---|---|
| Type 1 (distal) | Cannot excrete acid in the distal tubule | Low | Above 5.5 | Kidney stones, calcium deposits in kidneys, bone disease, growth failure |
| Type 2 (proximal) | Cannot reabsorb bicarbonate | Low | Variable (can be below 5.5) | Rickets or osteomalacia, often with Fanconi syndrome |
| Type 4 (hyperkalemic) | Low aldosterone or resistance to it | High | Usually below 5.5 | High potassium; usually mild acidosis |
Type 3 is a rare mixed form.
Type 1 (distal) RTA
- Inherited forms often appear in infancy or childhood with vomiting, poor growth and kidney calcification; some include hearing loss.
- Acquired causes: Sjögren's syndrome, lupus, rheumatoid arthritis, autoimmune hepatitis, medicines (amphotericin B, lithium, ifosfamide), sickle cell disease, obstruction and kidney transplant rejection.
- Leads to kidney stones, nephrocalcinosis and low potassium.
Type 2 (proximal) RTA
- Often part of Fanconi syndrome, where the proximal tubule also wastes glucose, phosphate, amino acids and uric acid.
- Causes: inherited conditions such as cystinosis in children, multiple myeloma, heavy metals, and medicines including tenofovir, ifosfamide and acetazolamide or topiramate.
- Phosphate loss causes rickets in children and osteomalacia in adults.
Type 4 RTA
- Most common type in adults.
- Caused by low aldosterone or the kidney's resistance to it.
- Causes: diabetic kidney disease, chronic kidney disease, Addison's disease, and medicines such as ACE inhibitors, ARBs, spironolactone, trimethoprim, NSAIDs, heparin and calcineurin inhibitors.
- Main issue is hyperkalemia.
Symptoms
Many people, especially with type 4, have no symptoms and are diagnosed from blood tests. Possible symptoms:
- tiredness and muscle weakness
- muscle cramps or, with very low potassium, paralysis
- rapid breathing
- kidney stones: flank pain and blood in urine
- bone pain, fractures, bowed legs in children
- poor growth and feeding problems in infants and children
- excessive urination and thirst
- palpitations from potassium imbalance
Diagnosis
- Blood tests: low bicarbonate with a normal anion gap (metabolic acidosis), potassium, chloride, kidney function.
- Urine pH and urine anion gap: help distinguish RTA from acid loss through diarrhea and identify the type.
- Bicarbonate loading or acid loading tests in specialist settings.
- Urine tests for glucose, phosphate and protein (Fanconi syndrome).
- Kidney ultrasound for stones and calcification.
- Tests for causes: autoimmune antibodies, protein electrophoresis for myeloma, aldosterone and renin, genetic testing in children.
Treatment
Alkali therapy
- Sodium bicarbonate or potassium citrate to neutralize acid.
- Type 1 usually needs modest doses and responds well; correcting acidosis prevents stones and supports growth in children.
- Type 2 often needs much larger doses because bicarbonate keeps being lost in urine.
- Potassium citrate both corrects acid and replaces potassium, and helps prevent kidney stones.
Potassium management
- Types 1 and 2: potassium supplements.
- Type 4: lower potassium through a low-potassium diet, stopping causative medicines, diuretics, potassium binders, and fludrocortisone in some cases.
Other treatments
- phosphate and vitamin D for Fanconi syndrome-related bone disease
- treating the underlying autoimmune disease, myeloma or obstruction
- stopping or changing causative medicines
Outlook
With treatment, most people with RTA do well. Children with inherited distal RTA who are treated early usually grow normally and avoid severe kidney damage. Untreated, RTA can lead to stunted growth, bone disease, recurrent stones and chronic kidney disease.
Frequently asked questions
What is renal tubular acidosis?
Renal tubular acidosis is a condition in which the kidney tubules cannot remove acid or keep enough bicarbonate, causing acid to build up in the blood. It can cause potassium problems, kidney stones, weak bones and poor growth.
What are the types of renal tubular acidosis?
The main types are type 1 (distal), where the kidney cannot excrete acid; type 2 (proximal), where bicarbonate is lost in urine; and type 4, caused by low aldosterone or resistance to it, which causes high potassium.
What causes renal tubular acidosis?
Causes include inherited gene mutations, autoimmune diseases such as Sjögren's syndrome and lupus, medicines such as lithium, amphotericin, tenofovir, ACE inhibitors and spironolactone, diabetes, kidney disease and multiple myeloma.
How is renal tubular acidosis treated?
It is treated with alkali supplements such as sodium bicarbonate or potassium citrate, along with potassium supplements or potassium-lowering measures depending on the type. Treating the underlying cause and stopping causative medicines are also important.
Is renal tubular acidosis serious?
It can be if untreated, causing growth failure, kidney stones, bone disease and dangerous potassium levels. With treatment, most people live normal lives. Children diagnosed early usually grow and develop normally.
Sources
This guide was written from current patient and clinical guidance, including:
- National Kidney Foundation: Renal tubular acidosis
- NIDDK: Renal tubular acidosis
- MedlinePlus: Distal renal tubular acidosis; Proximal renal tubular acidosis
- Merck Manual Professional: Renal tubular acidosis
- European Society for Paediatric Nephrology: Clinical practice recommendations for distal RTA