ABSTRACT
Close monitoring of serum calcium levels is commonly used to identify postoperative hypoparathyroidism, but an ideal intraoperative assessment of parathyroid function is lacking. An intraoperative parathyroid hormone assay [quick PTH assay] has been increasingly adopted to monitor the success of parathyroid and thyroid surgery. The aim of this study is to evaluate the utility of the quick PTH assay to monitor parathyroid function during thyroidectomy. This study was conducted on 35 patients undergoing bilateral or complete thyroidectomy for various thyroid pathologies. Twenty five palients in the test group [at risk of developing clinically significant hypocalcaemia] were classified into two subgroups : group 1 contained patients who did not develop postoperative hypocalcaemia [n = 17] and group 2 wre patients who developed postoperative symptomatic hypocalcemia requiring either calcium supplements [n = 5] only or vitamin D analogue in addition [n = 3] on discharge from the hospital. Ten patients who underwent unilateral thyroid lobectomy without any risk of developing symptomatic hypocalcemia were used as control patients. In both groups, the pre and postoperative serum or plasma calcium values, quick immunochemiluminometric PTH assay and standard PTH assay were performed. The percentage decline of quick PTH immediately after completion of thyroidectomy [0 minutes] compared with that at induction in group 2[87.4 +/- 3.8%] was significantly greater than those in control group [32.5 +/- 6.4%] and group 1 [35.1 +/- 4.8%] [P < .001]. The decline of 92.3 +/- 3.2% in group 2 was significantly higher than the decline of 43.5 +/- 3.8% in group l [P < .001] and that of 37.8 +/- 5.6% in control group [P < .001] at 10 minutes compared with those at induction. There was no difference in the percentage quick PTH decline after thyroidectomy between control group and group 1. The PTH measurement by standard IRMA assay on the morning after operation was significantly lower in group 2 [3.1 +/- 1.6 pg/mL] compared with those in control group [23.6 +/- 2.4 pg/mL] [P < .001] and group 1 [24.1 +/- 1.4 pg/mL] [P < .001]. The calcium level was significantly lower in group 2 compared with that in group 1 on the morning after operation [P < .001] but the difference in early postoperative calcium level [within 6 hours] between these two groups did not reach statistical significance [P = .06], However, calcium levels both within 6 hours and on the morning after operation in group 2 patients were significantly lower than those in group I [P =.001 and P < .001]. The correlation between the quick PTH assay after thyroidectomy and the standard PTH assay by IRMA was determined, and the correlation coefficient was 0.68 [r[2], 0.028], with P < .0001. Both the quick PTH assay and consecutive early calcium measurements are accurate in predicting postoperative normocalcemia. However, the quick PTH assay is available within 15 to 20 minutes after operation, but serum calcium monitoring requires at least 24 hours, as well as an additional 4-hour turnover time, before the results are available