Synopsis
Recognise generalised proximal tubular solute wasting, identify acquired and inherited causes, and replace phosphate, alkali and potassium through safe specialist monitoring.
- Fanconi syndrome is a generalised proximal-tubule reabsorptive defect, not Fanconi anaemia, and produces urinary loss of several filtered solutes rather than one isolated abnormality.
- Core clues include phosphate wasting, normoglycaemic glycosuria, aminoaciduria, bicarbonate loss causing proximal RTA, urate loss, potassium loss and low-molecular-weight proteinuria.
- A normal creatinine does not exclude substantial proximal dysfunction because tubular transport can fail before glomerular filtration falls.
- Acquired causes include monoclonal light-chain proximal tubulopathy, tenofovir disoproxil, ifosfamide, cisplatin, outdated tetracycline exposure and heavy metals; the precise medicine and host risk matter.
- Inherited causes present more often in childhood but can reach adult services; cystinosis, Dent and Lowe syndromes, hereditary fructose intolerance, tyrosinaemia and mitochondrial disorders have distinctive extrarenal features.
- Renal phosphate wasting causes defective mineralisation, bone pain, proximal weakness, insufficiency fractures or rickets, sometimes before the kidney diagnosis is recognised.
- Pair serum and urine samples to establish inappropriate urinary loss; urine glucose in the presence of normal blood glucose is a particularly useful bedside clue.
- Management requires removal or treatment of the cause plus individual replacement of water, bicarbonate, potassium and phosphate; oversupplementation can cause diarrhoea, hyperkalaemia or nephrocalcinosis.
Key red flags
Bone pain, waddling gait, proximal weakness and insufficiency fractures with low phosphate may represent renal-wasting osteomalacia rather than osteoporosis alone.
Rising creatinine, hypophosphataemia and glycosuria during tenofovir disoproxil or ifosfamide exposure should trigger targeted renal safety review.
Investigation priorities
Demonstrate inappropriate renal loss of phosphate, glucose, urate, bicarbonate and potassium.
Management branches
Hypophosphataemia, glycosuria or tubular proteinuria suggests proximal dysfunction.
- Repeat serum phosphate, bicarbonate, potassium, glucose, urate, magnesium and creatinine while collecting appropriately timed urine chemistry.
- Demonstrate at least a coherent pattern of inappropriate urinary losses rather than diagnosing Fanconi syndrome from isolated glycosuria.
- Assess symptoms and ECG where needed, admitting for severe phosphate or potassium depletion, dehydration, rhabdomyolysis or neurological compromise.
Key medicines
Oral phosphate saltsStart only with renal or metabolic specialist advice, using divided local-formulary doses titrated to symptoms, serum phosphate and urinary calcium rather than normalising one result rapidly.Can cause diarrhoea, secondary hyperparathyroidism, hyperphosphataemia and nephrocalcinosis. Dose requirements change as tubular function and GFR change.
Alfacalcidol or calcitriolUse only for a defined specialist indication with an agreed low starting dose and frequent calcium, phosphate and urine-calcium surveillance.Hypercalcaemia, hypercalciuria, stones and nephrocalcinosis can result; native vitamin-D deficiency should be assessed separately and pregnancy requires specialist review.