How is phosphorus handled by the kidney?
The kidney filters between 3700 and 6100 mg of phosphate a day. Phosphate excretion is about 600 to 1500 mg/day, so about 75% to 85% of filtered phosphate is reabsorbed by the kidney. The proximal tubule reabsorbs about 85% of the filtered load via a triad of sodium-phosphate cotransporters (NaPi-2a, NaPi-2c, PiT-2). Phosphate reabsorption is regulated by numerous dietary, metabolic, and hormonal factors. Calculating the tubular reabsorption of phosphorous (TRphos) can provide insight into renal phosphorus handling.
Factors that lead to increased renal phosphate absorption include a low phosphate diet, 1,25-OH vitamin D, and thyroid hormone. On the other hand, parathyroid hormone (PTH), fibroblast growth factor (FGF)23, a high phosphate diet, metabolic acidosis, potassium deficiency, glucocorticoids, dopamine, hypertension, and estrogen lower phosphate absorption.