Synopsis
Classify renal tubular acidosis from acid-base and potassium physiology, identify reversible causes, and replace alkali safely without missing an electrolyte emergency.
- RTA is a renal acidification defect that usually causes a normal-anion-gap, hyperchloraemic metabolic acidosis out of proportion to any reduction in glomerular filtration.
- First confirm genuine metabolic acidosis and exclude gastrointestinal bicarbonate loss, chloride-rich fluid administration, ketoacidosis masked by mixed disorders, toxins and advanced CKD.
- Distal type 1 RTA impairs urinary hydrogen secretion, often leaves urine inappropriately alkaline during systemic acidosis, and is associated with hypokalaemia, hypocitraturia, stones and nephrocalcinosis.
- Proximal type 2 RTA reflects bicarbonate wasting; urine becomes acidic after plasma bicarbonate falls below the reduced reabsorptive threshold, and generalised proximal loss indicates Fanconi syndrome.
- Type 4 RTA is characterised by hyperkalaemia from deficient or ineffective aldosterone action, commonly with diabetic kidney disease, interstitial disease or medicines affecting the renin-aldosterone-distal sodium pathway.
- Urine pH is only interpretable in a fresh sample during confirmed acidosis; urea-splitting infection, diet, low distal sodium delivery and sample delay can mislead.
- Treatment combines cause removal with potassium management and individually titrated bicarbonate or citrate; proximal RTA often needs much more alkali than distal disease.
- Potassium citrate can be useful in hypokalaemic stone-forming distal RTA but is dangerous in hyperkalaemia or significant renal impairment and belongs under specialist monitoring.
Key red flags
Mild metabolic acidosis with persistent hyperkalaemia in diabetic or interstitial CKD, especially during RAAS or ENaC-blocking therapy, suggests type 4 physiology.
Palpitations, syncope, ascending weakness or paralysis can result from severe potassium disturbance and require immediate ECG and biochemical assessment.
Investigation priorities
Confirm metabolic acidosis and assess severity and respiratory compensation.
Management branches
Routine chemistry shows a low bicarbonate concentration.
- Repeat or obtain a blood gas when artefact or respiratory alkalosis is possible, while checking chloride, potassium, renal function, glucose, lactate and ketones.
- Calculate and albumin-adjust the anion gap, then seek diarrhoea, urinary diversion, saline administration, toxins and reduced-GFR explanations.
- Collect fresh urine pH, culture and electrolytes before alkali when clinically safe, and involve nephrology if the physiology remains mixed or uncertain.
Key medicines
Sodium bicarbonateFor chronic renal tubular acidosis, initiate and titrate using the current BNF and specialist plan; the required dose varies substantially with subtype and ongoing bicarbonate loss.Monitor sodium load, blood pressure, oedema, potassium and gastrointestinal tolerance. Large doses may be required in proximal RTA and can worsen hypokalaemia.
Potassium citrate with potassium bicarbonateUse only through a renal or metabolic stone service, divided and titrated to potassium, bicarbonate and urine citrate using the live BNF product guidance.Avoid or use extreme caution with hyperkalaemia, interacting potassium-raising drugs or impaired excretion; gastrointestinal injury and rapid potassium change are important risks.