Left-shifted relation between calcium and parathyroid hormone in graves' disease

Abstract

Background: Patients with Graves' disease (GD) have disturbances in calcium regulation with manifestations such as postoperative hypocalcemia. We have investigated the thyroid as well as the parathyroid function in detail. Materials and Method: A series of patients undergoing total thyroidectomy for GD (n = 56) or multinodular goiter (MNG; n = 50) were scrutinized for postoperative hypocalcemia and a need for calcium and/or vitamin D substitution. A citrate-calcium (CiCa) clamp was used in 14 patients and 21 controls to quantify the secretion of PTH in relation to the ionized plasma calcium level. The set point, equal to the plasma-ionized calcium concentration at which 50% of the maximal secretion of PTH is inhibited, as well as other CiCa-related parameters were calculated. Results: Hypocalcemia was present in48%ofGDand 41.2% of patients withMNGpostoperatively. Patients withGDhad lower calcium levels,18%had serum Ca less than 2.00 mmol/L compared with 4.0% in the MNG group (P = .02). A higher degree of GD patients were given parenteral calcium substitution during the hospital stay (3.6% vs 0%) and oral calcium substitution at discharge (48% vs 10%), although they had normal vitamin D3 levels. The GD group showed a significantly leftshifted set point compared with the normal group on the CiCa clamp, 1.16 mmol/L vs 1.20 mmol/L (P