Hypocalcemia following thyroid surgery: incidence and risk factors. A longitudinal multicenter study comprising 2,631 patients.

Postoperative hypocalcemia is the most frequent complication of total thyroidectomy. It may have a delayed onset, and therefore delays the discharge from the hospital, requiring calcium replacement therapy to alleviate clinical symptoms. During a 7-month period, 2,631 consecutive patients undergoing primary or completion thyroidectomy were prospectively followed up and underwent analysis regarding postoperative hypoparathyroidism. Data were prospectively collected by questionnaires from 39 Italian endocrine surgery units affiliated to the Italian Endocrine Surgery Units Association (Club delle Unità di EndocrinoChirurgia-UEC), where thyroid surgery is routinely performed. The incidence of hypoparathyroidism was 28.8 % (757 patients), including transient hypocalcemia (27.9 %-734 patients) and permanent hypocalcemia (0.9 %-23 patients). The rate of asymptomatic hypocalcemia was 70.80 %. The incidence of permanent hypocalcemia was higher in the symptomatic hypocalcemia group (7.5 %) than in asymptomatic one (1.5 %). Female patients experienced a transient postoperative hypocalcemia more frequently than male patients (29.7 and 21.2 %, respectively; p < 0.0001). The percentage developing hypocalcemia in patients in which parathyroid glands were intraoperatively identified and preserved was higher than in the patients in which the identification of parathyroid glands was not achieved (29.2 vs. 18.7 %, p < 0.01). This prospective study confirmed the main risk factors for postoperative hypocalcemia: thyroid cancer, nodal dissection, and female gender. It farther showed that identifying parathyroids has an important role to prevent permanent hypocalcemia though with a higher risk of transient hypocalcemia. A suitable informed consent should especially emphasize the importance of some primary factors in increasing the risk of hypocalcemia after thyroid surgery.