Publication:

The utility of serum 25-hydroxyvitamin D in predicting post-thyroidectomy hypocalcemia in thyrotoxic subjects: a single-center cohort study

Background The role of preoperative vitamin D deficiency as a predictor of post-thyroidectomy hypocalcemia in thyrotoxic subjects is controversially reported. This prospective cohort study determined the utility of serum 25-hydroxyvitamin D (25OHD) levels in predicting transient hypocalcemia in thyrotoxic and euthyroid patients undergoing total thyroidectomy (TT).

Methods Subjects with new-onset hyperthyroidism (n=97; age=median (Inter-Quartile Range); 38 (18) years; M:F=25:72) and age; sex-matched euthyroid cohorts (n=231; age=37 (18) years; M:F=40:191) undergoing TT were evaluated for serum corrected-calcium, intact parathormone and 25OHD levels at baseline, 48-hour and 6-months post-TT, p value <0.05 was considered significant.

Results The incidence of transient hypocalcemia in thyrotoxic subjects was 58.8% (57/97) versus 22.5% (52/179) in euthyroid cohorts. In receiver operating characteristic analysis predicting transient hypocalcemia for the test-variable preoperative 25OHD, the area under curve (AUC) among euthyroid subjects was 0.725 (95% CI: 0.641-0.809; p<0.001) with a threshold of 17.6 ng/mL with sensitivity and specificity of 65.4% and 64.2% respectively. In thyrotoxic subjects, the AUC was 0.573 (95% CI; 0.452-0.694; p=0.222) with poorer predictability and was less than that of euthyroid subjects.

Conclusions Preoperative 25OHD below 17.6 ng/ml was reliable in predicting transient postoperative hypocalcemia in euthyroid subjects though with a limited sensitivity and specificity but unreliable in thyrotoxic subjects undergoing TT.