Frequency of Hypomagnesaemia following Total and Near-total Thyroidectomy and its relationship with Hypocalcaemia

To determine the frequency of hypomagnesaemia in patients undergoing thyroidectomy and evaluate its relationship with postoperative hypocalcaemia.

Observational, cross-sectional study.

Surgical Unit 1, Benazir Bhutto Hospital, Rawalpindi, Pakistan from April 2017 to May 2019.

Preoperative and 24-hour postoperative samples for serum calcium and magnesium of 75 patients undergoing total and near-total thyroidectomy were taken.  Postoperative signs and symptoms of hypocalcaemia were documented. Data was analysed on SPSS version 22, using independent and paired t-test, Pearson correlation, linear regression, Chi-square test and Fisher's Exact test.

Postoperatively 49 (65.3%) patients developed hypocalcaemia and 8 (10.7%) developed hypomagnesaemia. Postoperative hypocalcaemia was significantly associated with hypomagnesaemia (p=0.03) with a significant positive linear correlation. Ten patients (13.3%) developed symptomatic hypocalcaemia; however, it was not associated with postoperative hypomagnesaemia. Postoperative hypocalcaemia and hypomagnesaemia were significantly associated with preoperative calcium level (p = 0.03 and 0.04, respectively). There was significantly lower calcium level in patients with hypomagnesaemia (p = 0.002) and a significant fall in magnesium level in patients developing hypocalcaemia (p = 0.044).

Postoperatively hypocalcaemia was prevalent following thyroidectomy, while hypomagnesaemia was not common.  Hypomagnesaemia and a fall in magnesium level after surgery was associated with hypocalcaemia; but not with symptomatic hypocalcaemia. Monitoring of magnesium levels in severe or persistent hypocalcaemia is recommended. While this study proves a relationship between calcium and magnesium, its clinical implication must be further studied. Key Words: Calcium, Magnesium, Postoperative, Hypocalcaemia, Hypomagnesaemia, Thyroidectomy.