Renal tubular acidosis !

Renal tubular acidosis is a group of kidney tubule disorders that fail to remove acid or keep bicarbonate, causing acid build-up in the blood.

Updated 2026-11-01

Structures involved

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Why it happens

What it is

A group of disorders in which the renal tubules cannot excrete acid or reabsorb bicarbonate properly, causing a normal anion gap (hyperchloraemic) metabolic acidosis while glomerular filtration is relatively preserved. Types 1 (distal), 2 (proximal) and 4 (hyperkalaemic) are taught.

Who gets it

Inherited forms are rare and present in infancy or childhood with poor growth. Acquired forms are more common in adults: type 4 is the most frequent overall, usually in diabetic kidney disease or with drugs that block aldosterone; type 1 is linked to autoimmune diseases such as Sjögren disease and lupus; type 2 to Fanconi syndrome, myeloma and drugs.

Causes

Type 1 (distal): inability to secrete H+ in the collecting duct; Sjögren disease, lupus, amphotericin B, lithium, hypercalciuria, inherited forms
Type 2 (proximal): failure to reabsorb bicarbonate; Fanconi syndrome, multiple myeloma, carbonic anhydrase inhibitors, tenofovir, ifosfamide, cystinosis, heavy metals
Type 4: low aldosterone or aldosterone resistance; diabetic kidney disease, ACE inhibitors, ARBs, potassium-sparing diuretics, heparin, trimethoprim, calcineurin inhibitors, adrenal insufficiency

Risk factors

Autoimmune disease (Sjögren disease, lupus, rheumatoid arthritis)
Diabetes with kidney disease
Multiple myeloma or light-chain disease
Nephrotoxic or aldosterone-blocking drugs
Family history or consanguinity (inherited forms)

Pathophysiology

In type 1 the alpha-intercalated cells cannot acidify the urine, so urine pH stays above about 5.5 despite acidosis; buffering by bone releases calcium and phosphate, causing hypercalciuria, kidney stones and nephrocalcinosis, with hypokalaemia. In type 2 the proximal tubule cannot reclaim filtered bicarbonate until plasma bicarbonate falls to a new low threshold, after which the urine can acidify; it often comes with Fanconi features (glucosuria, aminoaciduria, phosphaturia) and hypokalaemia. In type 4, lack of aldosterone action reduces potassium and ammonium excretion, producing hyperkalaemia with a mild acidosis.

Classification

Type 1, distal: urine pH > 5.5, low potassium, stones
Type 2, proximal: urine pH < 5.5 once bicarbonate is low, low potassium, Fanconi features, rickets or osteomalacia
Type 4, hypoaldosteronism: urine pH < 5.5, high potassium, most common
Type 3 (mixed) is rare and mostly historical

Symptoms and signs

Often found by laboratory tests: low bicarbonate with a normal anion gap
Children: failure to thrive, poor growth, vomiting, rickets
Muscle weakness, cramps or paralysis from low potassium (types 1 and 2)
Kidney stones and renal colic (type 1)
Bone pain and fractures (osteomalacia)
Palpitations or weakness from high potassium (type 4)

Diagnosis

Clinical: Suspected in normal anion gap metabolic acidosis without diarrhoea; history of autoimmune disease, drugs, diabetes, stones and growth in children.
Tests: Arterial or venous blood gas and electrolytes with anion gap; serum potassium (low in types 1 and 2, high in type 4); urine pH; urine anion gap (positive in RTA, negative in diarrhoea); urine calcium, glucose, phosphate and amino acids for Fanconi features; renin and aldosterone in type 4; serum and urine protein electrophoresis, anti-Ro/La antibodies as indicated. Specialised acid or bicarbonate loading tests are rarely needed.
Imaging: Kidney ultrasound or non-contrast CT for nephrocalcinosis and stones (type 1); skeletal X-rays for rickets or osteomalacia.

Differential diagnosis

Diarrhoea (normal anion gap acidosis with a negative urine anion gap)
Chronic kidney disease with acidosis
Saline-induced hyperchloraemic acidosis
Ureteral diversion into the bowel
Carbonic anhydrase inhibitor effect

Goal of treatment

Correct the acidosis and potassium disorder, prevent stones and bone disease, allow normal growth in children and treat the underlying cause.

Treatment

Medical: Alkali therapy with bicarbonate or citrate salts; type 1 needs modest amounts, type 2 needs much larger amounts because bicarbonate is lost in the urine; potassium citrate when potassium is low.
Medical: Type 4: stopping drugs that raise potassium, a low-potassium diet, loop or thiazide diuretics, potassium binders and mineralocorticoid replacement when aldosterone is deficient and the patient is not hypertensive or overloaded.
Medical: Treating the cause: Sjögren disease or lupus, myeloma, withdrawing the culprit drug; vitamin D and phosphate for bone disease in proximal RTA.
Follow-up: Monitoring: bicarbonate, potassium and creatinine; growth curves in children; stone and nephrocalcinosis follow-up; ECG with severe potassium changes.

Complications

Nephrolithiasis and nephrocalcinosis (type 1)
Rickets, osteomalacia and growth failure
Severe hypokalaemia with paralysis or arrhythmia (types 1 and 2)
Hyperkalaemia with arrhythmia (type 4)
Progressive chronic kidney disease

Prognosis

Good when the acidosis is corrected early: children can reach normal growth and stones are prevented. The outlook of acquired forms depends largely on the underlying disease.

Test yourself

Think of the answer, then tap the question to see it.

Which type of renal tubular acidosis causes hyperkalaemia?

Type 4, due to low aldosterone or aldosterone resistance (often diabetic kidney disease).

Which RTA type is associated with kidney stones and a urine pH persistently above 5.5?

Type 1, distal renal tubular acidosis.

Which RTA type is associated with Fanconi syndrome and multiple myeloma?

Type 2, proximal renal tubular acidosis.

What kind of anion gap do the renal tubular acidoses produce?

A normal anion gap (hyperchloraemic) metabolic acidosis.

How does the urine anion gap help separate RTA from diarrhoea?

It is positive in RTA (low ammonium excretion) and negative in diarrhoea (high ammonium excretion).

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Renal Tubular Acidosis (NIDDK (National Institutes of Health), 2024); Distal renal tubular acidosis: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2024).

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Representative model, for educational purposes only.

Kidneys highlighted on the Durgical 3D model