Same-day surgery discharge after thyroidectomy should be accompanied by prophylactic calcium treatment when needed. We aimed to investigate how 4-hour parathormone determination after thyroidectomy ("4hPTH") performs for predicting hypocalcemia.

Preoperative parathormone (pg/mL) ("prePTH") and 4hPTH were determined in 38 consecutive patients after total (n=32) or completion thyroidectomy (n=6). They were discharged on postoperative day one and received prophylactic calcium and calcitriol treatment when sustaining hypocalcemia (albumin-adjusted total calcium ≤8mg/dL; "POD1hypoCa"). Parathormone decay percentage from prePTH to 4hPTH ("%∆4hPTH") was compared with 4hPTH in predicting POD1hypoCa and assessed by receiver operating curves (ROC). Youden index J was calculated for providing their cut-off associated criteria.

Parathormone values comparing patients with (n=7) or without (n=31) POD1hypoCa were: prePTH mean(SD) 58(24) vs. 64(24), p=0.56; 4hPTH 12(10) vs. 35(20), p<0.001; and %∆4hPTH 75(20) vs. 40(35), p=0,018. Area under the curve (AUC) from ROC analysis for POD1hypoCa prediction was similar for %∆4hPTH and 4hPTH: AUC(SD) 0,8(0,08) vs. 0,85(0,07), p=0.067. Cut-off associated criteria were >62% and <15.6pg/mL. Sensibility and specificity for predicting POD1hypoCa using these criteria were: %(SD) 85(14) vs. 71(17), p=1.00; and 67(8) vs. 87(6), p=0.031. False positives patients (patients falsely predicted as POD1hypoCa) were higher using the cut-off value for %∆4hPTH than using the one for 4hPTH (32% vs. 13% of patients; p=0.031).

1.4hPTH works better than %∆4hPTH, minimizing the rate of false positive patients which may be overtreated by initiating calcium the same day of surgery. 2.4PTH and %∆4hPTH may be useful for deciding prophylactic calcium treatment when planning discharge on the same day of surgery.