Vitamin D Does Not Affect Intraoperative Parathyroid Hormone Kinetics: A Mixed Linear Model Analysis.

BACKGROUND: Intraoperative parathyroid hormone (ioPTH) monitoring is used to confirm completeness of resection in patients undergoing parathyroidectomy for primary hyperparathyroidism (pHPT). Though there is an inverse relationship between vitamin D and parathyroid hormone (PTH), previous studies have suggested that 25-hydroxyvitamin D (25OHD) level does not affect the likelihood of meeting the Miami criterion. Here, we further investigate whether preoperative 25OHD level affects ioPTH kinetics. METHODS: This is a retrospective case-control study of patients undergoing parathyroidectomy for pHPT at a tertiary referral center. Patients were categorized based on preoperative 25OHD level as vitamin D deficient (≤ 20 ng/mL), insufficient (21-30 ng/mL), or sufficient (>30 ng/mL). Differences in baseline characteristics were analyzed with Kruskal-Wallis H test or chi-square analysis. ioPTH kinetic curves were analyzed using a log-transformed mixed linear model with subject-level random effects. Significance was set at P < 0.05. RESULTS: Among 630 patients who met inclusion criteria, there was a significant difference in ioPTH between groups at baseline (P < 0.001), but not at any other time point. As a continuous variable, as well as a categorical variable, in a mixed linear model, vitamin D had no significant effect on ioPTH kinetics. CONCLUSIONS: Despite a difference in preoperative and baseline PTH levels, preoperative 25OHD had no significant effect on ioPTH kinetics. Therefore, ioPTH assays can be used and interpreted uniformly, regardless of patients' vitamin D status.