The sensitivity and specificity of methylene blue spray to identify the parathyroid gland during thyroidectomy

Background Hypocalcemia is a common complication of thyroidectomy resulting from an injury to the parathyroid gland. Methylene blue, which is a medication and dye that has been used for more than a century, is safe and readily available. The previous study has found that methylene blue spray on the surgical field is absorbed by the parathyroid gland faster than in the perithyroidal area. This study was aimed to evaluate the diagnostic value of methylene blue spray to identify the parathyroid gland during thyroid lobectomy. Methods Patients who underwent thyroid lobectomy were recruited. After the recurrent laryngeal nerve was identified, methylene blue was sprayed onto the thyroid bed. After 5 min, the thyroid bed was inspected for areas in which the blue color had been rapidly absorbed. Biopsies were conducted for histopathology at both the stained area and the area in which the color had faded. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated. Results A total of 47 patients participated in this study. The sensitivity of methylene blue spray to identify the parathyroid gland during thyroid lobectomy was 92.31% (95% CI [63.97–99.81]) and specificity was 56.79% (95% CI [45.31–67.76]). The PPV was 25.53% (95% CI [20.34–31.53]) and NPV was 97.87% (95% CI [87.39–99.67]). There were no patients with post-operative hypocalcemia, allergic reactions to the methylene blue, or methylene blue toxicity. Conclusion The methylene blue spray could serve as a screening tool for identification of the parathyroid gland.