MAXIMUM TUBULAR REABSORPTION OF PHOSPHATE (TmP) IN HYPERPARATHYROIDISM*

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Abstract
Maxi-mum tubular reabsorption of phosphate (TmP) was measured by infusing neutral isotonic phosphate solution until tubular reabsorption of phosphate (calculated by creatinine clearance and urinary phosphate levels) became a constant value. Eight patients with surgically proven hyperparathyroidism were studied. It was possible to define what appeared to be a TmP in each instance. The values ranged from 1.1 mg. to 4.9 mg. per minute with a mean of 3.7 mg. per minute, and overlapped widely with normal values obtained by others. In 5 patients, TmP measurements were repeated postoperatively. TmP rose in 1, remained unchanged in 2, and fell in 2 patients. The mean value was 3.15 mg. per minute preoperatively and 3.67 mg. per minute postoperatively. Other indices of phosphate excretion in the 8 patients (tubular reabsorption of phosphate and phosphate clearance) failed to differ consistently from the normal range. It was concluded that TmP, measured as described, did not correlate consistently with parathyroid activity, owing to lack of standardization of other unknown factors that influence phosphate excretion.