Endocrine Abstracts

Patients with Grave’s disease (GD) are more prone to develop low serum calcium values than patients operated on because of goitre after total thyroidectomy. Moreover, some patients with GD achieve hypercalcemia probably due to active bone disease. We have used citrate-calcium clamping (CiCa) in order to investigate the calcium homeostasis in detail in patients with Grave’s disease.

Material and method: Our series of patients undergoing total thyroidectomy for GD (n=xx) and gioter (n=yy) were scrutinized for postoperative hypocalcemia and need for calcium and/or vitamin D substitution. CiCa-clamp (Schwarz P, Sörensen HA 1992, 1993) were used in 11 patients and 24 controls to quantify the secretion of PTH in relation to ionized plasma calcium level. The wet 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: The rate for having hypocalcemia was 48% in our patients overall, but patients with GD have lower calcium levels, 16% had < 2.00 mmol/l compared to 4.5% in the goiter group; need more calciumsubstitution during the hospital stay (6.5 vs 5.1%) and at discharge (33.2 vs 12.9%).

The GD group have a significant more left sided set point than the normal group, 1.14 vs 1.20 mmol/l P<0.001 (Mann–Withney U test) as well as an increased response in release of PTH to hypocalcemic stimulus.

Conclusion: Patients with GD have a left-shifted calcium/PTH set point compared to normal controls. We also noted a faster and higher level of PTH response to hypocalcemic stimuli in GD, presumably related to known derangements in these patients, such as high bone turnover. The CiCa response mimicks that of obese patients in which vitamin D insufficiency has been proposed as an underlying cause.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This work was supported, however funding details unavailable.