Possible role of low magnesium levels in the onset of postoperative hypoparathyroidism following thyroidectomy

BACKGROUND: A positive correlation between calcium and magnesium serum levels is well known and depends upon various factors. This study aims at verifying the existence of this association in a retrospective series of patients who underwent thyroid surgery. METHODS: Two hundred eighty-five consecutive patients (202F, 83M, mean age 57 years) who underwent at least total thyroidectomy (TT) and had a complete clinical and biochemical pre- and postoperative evaluation were included in the study. Patients were evaluated with regard to: sex, age, indications for surgery, operative time, number of accidentally removed parathyroids, extent and time of surgery, thyroiditis, final histology, pre- and postoperative levels of calcium, magnesium, vitamin D, and creatinine, presence of symptoms of hypocalcaemia. Statistical analysis was performed using the "R" software. RESULTS: In the postoperative period, biochemical hypocalcaemia (<8.5mg/dL) was observed in 126 patients (44%) and severe hypocalcaemia (<7.5mg/dL, a level indicating the need for longer hospitalization) was seen in 40 (14%). When analysing patients with and without postoperative hypocalcaemia, the factors affecting postoperative biochemical hypocalcaemia were: older age (p=0.019), longer operative time (p=0.039), and a highly significant correlation between postoperative calcium and magnesium levels (r = 0.432; p<0.001). CONCLUSIONS: The only factor among the ones we analysed in this retrospective study that would appear to be linked to the onset of clinically relevant hypocalcaemia is low magnesium levels in the postoperative period. A prospective randomized study with a group of patients undergoing magnesium replacement in the postoperative period can clarify the possible role of magnesium repletion on hypocalcaemia.