Value of the 6-Hour Postoperative Ionized Calcium Slope in Predicting Post- Thyroidectomy Occurrence of Hypocalcemia

Objective: To determine the value of the 6-hour postoperative ionized Calcium (iCa) slope, versus 6-hour postoperative Calcium alone, in predicting the occurrence of hypocalcemia in patients who underwent thyroid surgery in a tertiary hospital in Metro Manila. Methods: Study Design:            Retrospective Cross-Sectional Study Setting:                       Tertiary Private Hospital Subjects:                    Pre-operative and 6-hour postoperative ionized calcium determinations were analyzed in 59 patients of the ENT-HNS department in a tertiary hospital in Metro Manila who underwent thyroid surgery from January 2009 to December 2013. Results: The 6-hr postoperative iCa slope (difference between the pre-operative and 6-hour postoperative iCa levels) of ≥0.18 mmol/L correctly predicted 57.1% of patients who eventually developed hypocalcemia, with a specificity of 81.6%, and a positive predictive value of 63.2%. In contrast, the 6-hour postoperative iCa measurement identified only 23.8% (5 out of 21) patients who developed hypocalcemia. Conclusion: The 6-hr postoperative iCa slope increased the probability of identifying patients who developed hypocalcemia from 23.8% to 57.1%. However, as a single determination, this may  not suffice to take the place of serial iCa measurements after thyroid surgery. Keywords: ionized calcium (iCa), hypocalcemia, thyroidectomy