POST-OPERATIVE SERUM PARATHYROID HORMONE LEVELS AS A PREDICTOR OF HYPOCALCEMIA IN PATIENTS UNDERGOING TOTAL THYROIDECTOMY

Abstract

BACKGROUND: Postoperative hypocalcemia is a common complication of total thyroidectomy and the incidence varies from 1 - 50%. Post-thyroidectomy hypocalcemia is due to parathyroid gland dysfunction, caused by devascularization, stunning or accidental removal of the glands along with the thyroid gland. Since the onset and severity of post-operative hypocalcemia is unpredictable, various attempts have been made to identify predictors of hypocalcemia. There has been an increasing interest in measuring serum parathyroid hormone (PTH) levels as an early predictor for the development of hypocalcemia after total thyroidectomy. Early detection allows for prompt supplementation of patients at risk, thus minimizing long term periodic calcium testing during follow up. Focus is placed on the timing of PTH measurement and the ability to predict which patients will develop hypocalcemia requiring supplementation. PTH levels drawn at differing time points, ranging from intraoperatively to postoperative day 1(POD1) have been taken into consideration in the various studies done regarding Hypocalcemia post thyroidectomy. It is because of the direct relation between PTH and calcium levels in blood. But despite the association, no specific guidelines regarding the use of PTH as a predictor of hypocalcemia is available. OBJECTIVES: 1. To estimate serum PTH levels pre operatively and at 4th and 12th hour post operatively for patients undergoing total thyroidectomy. 2. To classify above patients as high risk (PTH < 12pg/ml ) or low risk (PTH > 12pg/ml), based upon a cut-off level of serum PTH. 3. To monitor and document the onset and severity of hypocalcemia in high risk group after prophylactic treatment and in low risk group without prophylactic treatment. MATERIALS AND METHODS: It is a prospective study conducted on 33 patients undergoing total/completion thyroidectomy from December 2018 to May 2020. The serum total calcium, albumin and PTH levels were tested on three occasions (Pre-op and 4th & 12th hour Post-op). Based upon Post-op 4th hour cut-off for PTH as 12pg/ml patients were further classified as High (<12pg/ml) and Low risk(>12pg/ml). Between both the Post-op levels of PTH, the one with better predictability of hypocalcemia was determined. Statistical analysis: Chi-square test was used as test of significance for qualitative data. Continuous data was represented as mean and SD. Independent t test was used as test of significance to identify the mean difference between two quantitative variables. Graphical representation of data: MS Excel and MS word was used to obtain various types of graphs such as bar diagram and Scatter plots. p value (Probability that the result is true) of <0.05 was considered as statistically significant after assuming all the rules of statistical tests. Statistical software: MS Excel, SPSS version 22 (IBM SPSS Statistics, Somers NY, USA) was used to analyze data. RESULTS: Post-op 4th hour PTH is better predictor of hypocalcemia than the Post-op 12th hour PTH, (in the post-operative period) as the association of former with serum ionized calcium level has more statistical significance than the later, (p value – 0.005 and 0.021 respectively). CONCLUSION: The patients who are at high risk for hypocalcemia, should be started with intravenous calcium and calcitriol supplementation. Serum PTH determination after four hours of total thyroidectomy is a relatively better predictor of hypocalcemia. and can guide selective calcium supplementation for those at high risk in the post-operative period. However, to determine the risk of Hypocalcemia at the end of 1 month of follow-up, both Post-op 4th and Post-op 12th hour PTH have similar diagnostic accuracy.