Direct Effect of the Correction of Acidosis on Plasma Parathyroid Hormone Concentrations, Calcium and Phosphate in Hemodialysis Patients: A Prospective Study

Abstract

Background: Metabolic acidosis contributes to renal osteodystrophy and together with hyperphosphatemia, hypocalcemia and altered vitamin D metabolism may result in increased levels of intact parathyroid hormone (iPTH) and metastatic calcifications. However, the impact of the correction of metabolic acidosis on iPTH levels and calcium-phosphate metabolism is still controversial. Study Design: The effects of the correction of metabolic acidosis on serum concentrations of iPTH, calcium (Ca), phosphate (PO₄) and alkaline phosphatase were prospectively studied. Twelve uremic patients on maintenance hemodialysis (HD) for 49 months (median; range 6–243 months) with serum bicarbonate levels ≤20 mmol/l were studied before and after 3 months of oral sodium bicarbonate supplementation. Predialysis serum bicarbonate, arterial pH, ionized calcium, plasma sodium, plasma potassium, serum creatinine, hemoglobin, K_t/V, postdialysis body weight, predialysis systolic and diastolic blood pressure were also evaluated before and after correction. Results: Serum bicarbonate levels and arterial pH increased respectively from 19.3 ± 0.6 to 24.4 ± 1.2 mmol/l (p < 0.0001) and 7.34 ± 0.03 to 7.40 ± 0.02 (p < 0.001). iPTH levels decreased significantly from 399 ± 475 to 305 ± 353 pg/ml (p = 0.026). No changes in total serum Ca, plasma PO₄, serum akaline phosphatase, K_t/V, serum creatinine, hemoglobin, body weight, predialysis systolic and diastolic blood pressures were observed. iCa decreased significantly. Conclusions: Our study demonstrates that the correction of metabolic acidosis in chronic HD patients reduces iPTH concentrations in HD patients with secondary hyperparathyroidism possibly by a direct effect on iPTH secretion.