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# 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

Tap one to see what it is and open it in 3D.

- [Kidneys](https://durgical.com/en/anatomy/kidney/)
- [Renal pelvis](https://durgical.com/en/anatomy/renal-pelvis/)
- [Ureters](https://durgical.com/en/anatomy/ureter/)
- [Left adrenal gland](https://durgical.com/en/anatomy/suprarenal-gland/)
- [Right adrenal gland](https://durgical.com/en/anatomy/suprarenal-gland-abdomen/)

## Why it happens

- [Renal handling of H⁺ and bicarbonate](https://durgical.com/en/physiology/renal-handling-of-h-and-bicarbonate/)
- [Metabolic acidosis, the anion gap and compensation](https://durgical.com/en/physiology/metabolic-acidosis-the-anion-gap-and-compensation/)
- [Proximal tubule transport](https://durgical.com/en/physiology/proximal-tubule-transport/)
- [Distal tubule and collecting duct](https://durgical.com/en/physiology/distal-tubule-and-collecting-duct/)
- [Anion gap and delta ratio](https://durgical.com/en/biochemistry/topics/anion-gap-and-delta-ratio/)
- [Kidney: cortex, medulla and the nephron](https://durgical.com/en/histology/kidney-cortex-medulla-and-the-nephron/)

## 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
- 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)

## Red flags

- Profound weakness or paralysis, or arrhythmias (severe hypo- or hyperkalaemia)
- Severe acidosis with fast breathing or altered consciousness
- Recurrent stones with declining kidney function (nephrocalcinosis)
- Bone pain, anaemia and high calcium in an older adult (myeloma)

## 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](https://durgical.com/en/anatomy/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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## Related conditions

- [Hypokalaemia](https://durgical.com/en/conditions/hypokalaemia/)
- [Hyperkalaemia](https://durgical.com/en/conditions/hyperkalaemia/)
- [Kidney stones (urolithiasis)](https://durgical.com/en/conditions/kidney-stones/)
- [Fanconi syndrome](https://durgical.com/en/conditions/fanconi-syndrome/)
- [Multiple myeloma](https://durgical.com/en/conditions/multiple-myeloma/)
- [Sjögren disease](https://durgical.com/en/conditions/sjogren-disease/)
- [Diabetic kidney disease](https://durgical.com/en/conditions/diabetic-kidney-disease/)
- [Rickets and osteomalacia](https://durgical.com/en/conditions/rickets-and-osteomalacia/)
- [Bartter, Gitelman and Liddle syndromes](https://durgical.com/en/conditions/bartter-gitelman-and-liddle-syndromes/)

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

Sources: [Renal Tubular Acidosis](https://www.niddk.nih.gov/health-information/kidney-disease/renal-tubular-acidosis) (NIDDK (National Institutes of Health), 2024); [Distal renal tubular acidosis: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000493.htm) (MedlinePlus (U.S. National Library of Medicine), 2024).

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Source: https://durgical.com/en/conditions/renal-tubular-acidosis/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/conditions/renal-tubular-acidosis/