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

The reasons of transient hypocalcemia, frequently occurring after thyroid s urgery, were investigated. Serum total calcium (seCa) and phosphorus (seP) levels were determined in 185 patients with benign nodular goiter before an d after thyroid surgery. Beside these, in 27 additional patients, serum mag nesium (seMg), total protein, albumin, calcitonin, parathormone (PTH) and 2 5-OH-D-3 vitamin (25-OH-D-3) levels were determined; corrected calcium (cCa ) values, reflecting ionized calcium concentrations, were calculated. The d aily changes of seCa and protein levels were measured in 20 patients. Anoth er twenty patients, undergoing non-endocrinological surgery served as contr ols. Transient, mild but significant decrease of seCa was observed after surgery while seP values were increased. Mild hypocalcemia (seCa <2.12 mmol/l) dev eloped in 18.4%, severe hypo-calcemia (seCa < 1.9 mmol/l) in 5.4% of the pa tients. The reduction of seCa levels was more pronounced in elderly, female patients. SeMg, total protein and albumin decreased, while cCa, PTH, calci tonin and 25-OH-D-3 values did not change. Positive correlation was demonst rated between the change of seCa and albumin levels. Similar results were o btained in the general surgery group. In the thyroid operated group, in cas e of severe hypocalcemia, PTH levels decreased significantly into the patho logical 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 hypoalbum inemia plays a role. The causal role of PTH, calcitonin and 25-OH-D-3 could not be proved in this study. Hypoparathyroidism can be responsible for the development of severe, prolonged hypocalcemia occurring at rare occasions.