Serum parathyroid hormone levels and renal handling of phosphorus in patients with chronic renal disease.

In eight patients with advanced renal insufficiency (inulin clearance 1.4-9.1 ml/ min), concentrations of serum calcium (S[CaJ) and phosphorus (S[PJ) were maintained normal (S[Ca] > 9.0 mg/100 ml, (S[P] < 3.5 mg/lOO ml) for at least 20 consecutive days with phosphate binding antacids and oral calcium carbonate. The initial serum levels of immunoreactive parathyroid hormone (S-PTH) were elevated in three (426-9230 pg/ml), normal in four (one after subtotal parathyroidectomy), and not available in one. The initial fractional excretion of filtered phosphorus ( Cp ) was high in all and ranged CIN from 0.45-1.05. Following sustained normo-calcemia and normo-phosphatemia, S-PTH was reduced below control levels in all patients; being normal in six and elevated in two. Cp decreased below CrN THE DECREASED fractional tubular reabsorption of phosphorus in patients with chronic renal disease has been attributed to concurring secondary hyperparathyroidism (1-3). However, the persistence of high fractional excretion of phosphorus after parathyroidectomy (4-6), even with demonstrable normal serum level of immunoassayable parathyroid hormone (6), supports the notion that additional factors other than secondary hyperparathyroidism may play an important role in the regulation of tubular reabsorption of phosphorus in patients with advanced chronic renal insufficiency. The fall in the fractional excretion of Received November 2, 1971. Supported by a grant (FR-S 1) from the General Clinical Research Centers Program of the Division of Research Resources, National Institutes of Health. control levels in all patients; it remained high in six (of which five had normal S-PTH) and was normal ( Cp = 0.01) in two (of which one had CIN elevated S-PTH). The observed relationship beCp d'h fi h tween S-PTH and -coul elt er re ect t e