Phosphate load and hyperphosphataemia
Stimulus · PO4 0.8-1.5 mmol/L
Serum phosphate is set by intake, renal excretion and exchange with bone. A phosphate load lowers ionised calcium by complexing it, and directly stimulates FGF23 from osteocytes and PTH from the parathyroid gland.
Detail
- Normal range
- About 0.8-1.5 mmol/L in adults, higher in growing children; roughly 85% of body phosphate is in bone
- Stimulates
- FGF23 secretion from osteocytes, and PTH secretion both directly and by lowering ionised calcium
- Excretion
- The kidney is the only meaningful route; 80-90% of filtered phosphate is reabsorbed in the proximal tubule
When it goes wrong
Tumour lysis syndrome after treating a bulky haematological malignancy
Hyperphosphataemia, hyperkalaemia and hyperuricaemia with hypocalcaemia from calcium-phosphate precipitation, causing tetany and acute kidney injury
Falling GFR in chronic kidney disease
Phosphate retention drives FGF23 and then PTH: the first step of chronic kidney disease-mineral and bone disorder
Refeeding after prolonged starvation
Insulin drives phosphate into cells: severe hypophosphataemia with rhabdomyolysis, respiratory muscle weakness and arrhythmia
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