The three types
Type 1 (Distal) Rta
- Defect in the distal tubule H+ ATPase
- Cannot acidify urine — urine pH stays >5.5 despite acidosis
- Low blood bicarb (often <15)
- LOW potassium
- Calcium-phosphate stones, nephrocalcinosis
- Causes: hereditary (SLC4A1, ATP6V1B1), Sjögren's, lupus, RA, lithium, amphotericin, ifosfamide, sickle cell
Type 2 (Proximal) Rta
- Defect in proximal bicarbonate reabsorption
- Bicarbonate threshold is low (~15-18) — urine pH can be variable
- LOW potassium
- Often part of Fanconi syndrome (glycosuria, aminoaciduria, phosphaturia, uricosuria → rickets/osteomalacia)
- Causes: multiple myeloma, light-chain disease, Wilson's, cystinosis, tenofovir, ifosfamide, lead, acetazolamide
TYPE 3 — historical (mixed type 1/2, very rare in children).
Type 4 (Hyperkalaemic) Rta
- Aldosterone deficiency or resistance
- Mild acidosis (bicarb 17-22), HIGH potassium
- Commonest type in clinical practice
- Causes: diabetes, ACE inhibitors/ARBs/spironolactone, NSAIDs, calcineurin inhibitors (tacrolimus, ciclosporin), Addison's, sickle cell, obstructive uropathy
Diagnosis
STEP 1 — confirm normal-anion-gap acidosis:
- Anion gap = Na - (Cl + HCO3); normal 8-12
- High-AG: lactic acid, ketones, toxins, uraemia
- Normal-AG: GI bicarb loss (diarrhoea) or renal bicarb loss (RTA)
STEP 2 — urine anion gap (UAG):
- UAG = Na + K - Cl (measured in urine)
- Negative UAG → GI loss (kidney working normally, excreting ammonium)
- Positive UAG → RTA (kidney not excreting acid)
STEP 3 — classify by potassium and urine pH:
- Low K + urine pH >5.5 + stones/nephrocalcinosis → Type 1
- Low K + bicarb falls quickly on therapy + Fanconi features → Type 2
- High K + diabetes/ACE/ARB → Type 4
Additional Tests
- Furosemide-fludrocortisone test (type 1)
- Sodium bicarbonate infusion (type 2 — fractional excretion of HCO3 >15%)
- Plasma aldosterone, renin (type 4)
- Urine calcium, citrate (type 1 stone risk)
- Genetic testing if hereditary suspected
Kidney Vitality is a daily multivitamin developed by a UK Consultant Nephrologist using renal nutrition principles. It contains no added potassium, magnesium, phosphorus or iron, and no herbal blends. See the formulation.
Treatment
Type 1
- Sodium bicarbonate 1-2 mmol/kg/day (often as Sodibic 500 mg tablets, 2-4 tds)
- Potassium citrate (Cytra-K) — replaces K and provides extra alkali
- Treat osteomalacia (vitamin D, calcium)
- Monitor for stone formation (citrate is also stone prevention)
- Treat underlying cause (e.g. Sjögren's)
Type 2
- Higher doses of bicarbonate needed (5-15 mmol/kg/day)
- K replacement (lost with bicarb)
- Thiazide diuretic can reduce bicarb dose (paradoxical effect)
- Treat Fanconi components: phosphate, vitamin D for osteomalacia
- Treat cause: stop tenofovir, treat myeloma, etc.
Type 4
- Stop ACE/ARB/spironolactone/NSAID if possible
- Low-K diet (avoid bananas, tomatoes, potatoes, oranges)
- Loop diuretic (furosemide) — wastes K, useful
- Fludrocortisone 50-200 mcg if true hypoaldosteronism (caution: BP, oedema)
- Patiromer or sodium zirconium cyclosilicate (SZC) for chronic hyperkalaemia
- Sodium bicarbonate if bicarb <22
- Often need to balance ACE/ARB benefit (renal/cardiac protection) against K rise — use K-binder rather than stopping ACE/ARB
Monitoring
- Bloods 1-2 weekly during dose titration, then 3-6 monthly
- Aim bicarbonate 22-26
- Aim K within normal range
- Monitor 24-hour urine: calcium, citrate, oxalate (especially type 1)
- DXA scan baseline + every 2 years (osteomalacia, especially types 1 and 2)
- Renal ultrasound annually if nephrocalcinosis/stones
- Children — growth charts; impaired growth is an indicator of inadequate treatment
When To Refer
- All suspected hereditary RTA (genetics, family screening)
- Type 1 with stones — to stone clinic + nephrology
- Type 2 — investigate for underlying cause (myeloma screen, heavy metals)
- Type 4 in CKD — close balance of ACE/ARB optimisation vs K-binder use
