Course of ionized calcium after thyroidectomy

The goal of the present study was to investigate the course of ionized calcium after thyroidectomy and to define a cut-off value that indicates symptoms of hypocalcemia.

The sample included 333 patients undergoing thyroidectomy at the University Hospital of UFMG between September 2000 and December 2005. Ionized calcium was determined before and after surgery (days 1, 2, and 30) in all patients and on postoperative days 90 and 180 in those with hypocalcemia. Asymptomatic patients received no calcium replacement therapy, irrespective of calcium concentration. Patients with clinical manifestation of hypocalcemia were treated after laboratory confirmation. The presence or absence of postoperative hypocalcemia was associated with ionized calcium concentration measured on the reported days.

Ionized calcium declined on the first two days after surgery in all patients when compared to preoperative levels (P = 0.000). Forty-seven (34.6%) of the 136 (40.8%) patients with postoperative hypocalcemia had symptoms. Patients with symptomatic hypocalcemia had significantly lower ionized calcium levels than those with asymptomatic hypocalcemia (P = 0.001). Fourteen (4.2%) patients progressed to definitive hypoparathyroidism by the end of 6 months.

Measurement of ionized calcium on postoperative days 1 and 2 is sufficient for the evaluation of post-thyroidectomy hypocalcemia. Ionized calcium concentrations <1.03 mmol/l on postoperative day 1 are indicative of the presence of symptoms and the need for treatment.