Metabolism of phosphate and calcium after severe accidental trauma

Hypophosphatemia is a common finding during the first 4-5 days after severe accidental trauma. We demonstrated that hypophosphatemia after trauma is caused by a definite decrease in renal phosphate threshold (TmPO4/GFR), that is the theoretical plasma phosphate concentration at which all of the filtered phosphate is reabsorbed by the renal tubules and renal excretion of phosphate is close to zero. We speculated that the decrease in renal phosphate threshold could be due to an increased activity of PTH which in turn could be the result of ionized hypocalcemia. In 7 patients with severe and in 8 patients with moderate trauma, however, we found ionized calcium and PTH levels to be within normal limits. Total plasma calcium was below normal (1.90-2.00 mmol/l) up to 20 days after trauma, probably due to a decreased plasma albumin concentration (25-30 g/l). We conclude, that ionized hypocalcemia and consecutive stimulation of PTH is not the cause of decreased renal phosphate threshold after severe accidental trauma.