Quick Intra-operative Parathyroid Hormone Assay in Predicting Hypocalcemia after Thyroidectomy

Abstract

Background: Despite the higher morbidity, total thyroidectomy is emerging as an attractive surgical option even for benign thyroid disease due to the risk of subclinical (occult) malignancy, the possibility of goiter relapse as well as of the increased risk of complications following reoperation ⁽¹⁾. Total thyroidectomy is now being performed as a short-stay or even an outpatient procedure at some medical centers. Postoperative hypocalcemia is common after total thyroidectomy, and perioperative monitoring of serum calcium levels is arguably the primary reason for overnight hospitalization. This study aimed to evaluate the accuracy and reliability of quick parathyroid hormone level measurement in predicting clinically relevant hypocalcaemia after total thyroidectomy. Methods: This was a prospective study carried out from January 2016 to December 2020 that included all patients who underwent either a total or a completion total thyroidectomy for benign or malignant disease. All patients were operated on and cared for by the same surgical team in Aswan University Hospital. Sixty out of three-hundreds cases who underwent   thyroid surgery for abnormal thyroid disorder and fulfil the criteria of total thyroidectomy were enrolled in the study.   Preoperative assessment: History: Physical examination, Investigations:  Routine preoperative assessment, Free T3, T4 and TSH assessment, Ionized serum calcium. PTH assay. Patients included in this study has been divided into two groups according to post thyroidectomy symptoms of hypocalcemia: Group I:  asymptomatic (no symptoms or signs of hypocalcaemia within 48 hours postoperatively).  Group II:  Symptomatic (positive symptoms or signs of hypocalcaemia within 48 hours postoperatively). Measurement of serum calcium and parathyroid hormone levels.Postoperative Management.Results: Statistical significance between Group Iand Group II according to Parathormone Hormone level and serum ionized calcium level.   The ROC curve cut-off value of parathormonepre-operatively to detect post-operative symptomatic group of hypocalcemia (Group II) after thyroidectomy is ≤ 74.3, Sensitivity 87.5%, Specificity64.64%, Positive predictive value 46.7%, and Negative predictive value 93.3%. The ROC curve cut-off value of serum ionized calcium pre-operatively to detect post-operative symptomatic group of hypocalcemia(Group II) after thyroidectomy is <1.11, Sensitivity 100%, Specificity 59.09%, Positive predictive value 47.1%, and Negative predictive value 100%. The ROC curve cut-off value of serum ionized calcium results to detect post-operative symptomatic group of hypocalcemia after thyroidectomy (Group II) is ≤ 1.06, Sensitivity 87.5%, Specificity 95.45%, Positive predictive value 87.5%, and Negative predictive value 95.5%. The changes of parathormone and ionized calcium levels between the preoperative and postoperative state in non- symptomatic group (Group I) and symptomatic group (Group II) of post thyroidectomy hypocalcemia; there was more changes in parathormone and ionized calcium (decline) in symptomatic group (Group II), but the change is more significant in ionized calcium level (p-value 0.001).Conclusion: Quick parathyroid hormone level measurement in accurate and reliabile in predicting clinically relevant hypocalcaemia after total thyroidectomy.