Magnesemia: an independent risk factor of hypocalcemia after thyroidectomy

Background: This study was designed to investigate the impact of serum magnesium (Mg) levels on hypocalcemia after thyroidectomy. Patients and methods: In total, 242 patients with differentiated thyroid cancer were retrospectively analyzed. Results: Multivariate regression analysis showed hypomagnesemia was an independent risk factor for hypocalcemia (P<0.001). While Mg in low levels (0.66 mmol/L <= Po-Mg <= 0.74 mmol/L) increased the risk of hypocalcemia, postoperative serum Ca (Po-Ca) levels were significantly lower in patients with hypomagnesemia than in patients with normomagnesemia (P=0.01), and the former patients suffered significant decreases in serum Ca (P=0.02). Compared to patients with a mild decline of serum Mg after surgery (Delta Mg <0.17), serum Ca decline significantly increased (P<0.001) in patients with a severe decline of serum Mg (Delta Mg >= 0.17), while the change in amounts of parathyroid hormone (PTH) after surgery was similar between the two groups (P>0.05). In patients with normal Po-Ca levels, hypomagnesemia increased the risk of symptoms related to hypocalcemia by 4.478 times (OR = 5.478, 95% CI 1.724-17.403). Conclusion: Hypomagnesemia, or even a low serum Mg level within the normal range, can increase the risk of hypocalcemia. After excluding the potential effects of PTH on serum magnesium and calcium, serum Mg reduction is one of the most important factors that influences postoperative serum Ca reduction. What's more, hypomagnesemia is closely linked with symptoms.