Prediction of early biochemical and symptomatic hypocalcemia in thyroid cancer patients after total thyroidectomy

Hypocalcemia is a common complication after total thyroidectomy (TT). Several studies have identified risk factors for early biochemical hypocalcemia, nevertheless, the noteworthy symptomatic hypocalcemia has not been considered. This study aims to construct an intuitive predictive model for biochemical and symptomatic hypocalcemia to assist individualized management.

A retrospective study was conducted on thyroid cancer patients undergoing TT. Two separate patient cohorts were used for model development and external validation, respectively. Data were gathered to identify the risk factors for biochemical (serum calcium <8.0 mg/dL) and symptomatic hypocalcemia by logistic regression. A predictive model was visualized by a nomogram and validated internally and externally.

Of 431 patients studied, 258 (59.9%) developed hypocalcemia including 180 with biochemical hypocalcemia and 196 with symptomatic hypocalcemia, of whom 118 patients had both. Female (OR 2.108, 95% CI 1.166-3.812, P = 0.014) and postoperative PTH decreased ratio ≥ 60% (OR 22.489, 95% CI 13.289-38.058, P < 0.001) were independent risk factors for hypocalcemia, while BMI ≥ 24 kg/m² (OR 0.567, 95% CI 0.331-0.970, P = 0.038) was a protective factor. Besides, Hashimoto's thyroiditis tended to increase the risk of hypocalcemia (P = 0.082). A nomogram was developed and a predicted probability of exceeding 0.55 suggested a higher risk of hypocalcemia with a sensitivity of 81.8% and a specificity of 82.1%. The internal and external validated areas under the curve (AUC) were 0.860 and 0.862, respectively.

The validated nomogram combining gender, BMI and proportion of PTH reduction may guide the risk identification and stratified management of hypocalcemia after total thyroidectomy.