Handling of phosphate by the transplanted kidney

Maximal tubular phosphate reabsorption capacity corrected for changes in glomerular filtration rate (TmP/GFR) was taken as a measure of renal phosphate handling in patients with good and stable functioning kidney allografts. TmP/GFR values were within the normal range in only one-fifth of the patients. Eighty per cent had an abnormally low renal phosphate threshold concentration. Persistent hyperparathyroidism was the causative factor of this diminished tubular reabsorption in less than half of these patients, the majority of them showing an iPTH independent phosphate leak. Although glucocorticoids, azathioprine and tubular damage of the graft in the perioperative phase may contribute to this iPTH independent phosphate wasting, no single causative factor could be identified. Cases with hypophosphataemia should be treated in order to avoid symptoms of phosphate depletion. Active Vitamin D metabolites would be the therapy of choice by suppressing the parathyroid glands ("chemical PTX") and by directly enhancing tubular phosphate reabsorption. In persistent hyperpathyroidism with hypercalcaemia, surgical parathyroidectomy must be considered. Therapy with phosphate salts is only symptomatic and should be used only as an adjunct.