Changes of serum calcium level following thyroid surgery--reasons and clinical implications.

The reasons of transient hypocalcemia, frequently occurring after thyroid surgery, were investigated. Serum total calcium (seCa) and phosphorus (seP) levels were determined in 185 patients with benign nodular goiter before and after thyroid surgery. Beside these, in 27 additional patients, serum magnesium (seMg), total protein, albumin, calcitonin, parathormone (PTH) and 25-OH-D3 vitamin (25-OH-D3) levels were determined; corrected calcium (cCa) values, reflecting ionized calcium concentrations, were calculated. The daily changes of seCa and protein levels were measured in 20 patients. Another twenty patients, undergoing non-endocrinological surgery served as controls. Transient, mild but significant decrease of seCa was observed after surgery, while seP values were increased. Mild hypocalcemia (seCa<2.12 mmol/l) developed in 18.4%, severe hypo-calcemia (seCa<1.9 mmol/l) in 5.4% of the patients. The reduction of seCa levels was more pronounced in elderly, female patients. SeMg, total protein and albumin decreased, while cCa, PTH, calcitonin and 25-OH-D3 values did not change. Positive correlation was demonstrated between the change of seCa and albumin levels. Similar results were obtained in the general surgery group. In the thyroid operated group, in case of severe hypocalcemia, PTH levels decreased significantly into the pathological range. It may be concluded that transient, mild postoperative hypocalcemia is not a thyroid surgery-dependent phenomenon; it can also be observed after other operations accompanied by similar blood loss; in its development hypoalbuminemia plays a role. The causal role of PTH, calcitonin and 25-OH-D3 could not be proved in this study. Hypoparathyroidism can be responsible for the development of severe, prolonged hypocalcemia occurring at rare occasions.