Participants
A retrospective study conducted on a group of patients who underwent total and subtotal thyroidectomy in 2018-2020 referred to Razi hospital in the north of Iran. The study was performed by the declaration of Helsinki and approved by the Ethics Committee of Guilan University of Medical Sciences (IR.GUMS.REC.1397.463). Inclusion criteria were indications for thyroidectomy (included any kind or suspicious mass or malignancies that had previously been confirmed by a pathology examination). Exclusion criteria were preoperative hypocalcemia, parathyroid adenoma, any underlying disease that affects parathyroid hormone levels, vitamin D, calcium, and albumin (such as chronic kidney disease, indigestion, and malabsorption), patient dissatisfaction participating in the study included a previous major procedure such as total laryngectomy or parathyroidectomy, receiving prophylactic drug therapy for osteoporosis, including calcium and vitamin D supplementation, and patients with hyperthyroidism and active Grave's.
Experimental design
Based on vitamin D levels before surgery, patients were divided into two groups with normal vitamin D (between 30-30 ng/ml) and vitamin D deficiency (less than 30 ng/ml). Then, postoperative calcium changes in patients were measured in two forms: normal calcium (8.5-5.5 mg/dl) and hypocalcemia (less than 8.5 mg/dl) based on vitamin D levels before surgery. Calcium, phosphorus, parathormone, and vitamin D levels were measured by the enzyme-linked immunosorbent assay (ELISA). Biotek microplate reader ELX-800, made in 750-400 nm microplates, has 4 filters, 630, 9090, 405 nm, source Tungsten light, and resolution are 0.001 OD. The status of thyroid tissue cytopathology was also calculated based on a biopsy performed according to the Bethesda standard. Based on this, the patient's pathology will be divided into 6 categories. Accordingly to (I) non-diagnostic; (ii) benign; (iii) an atypically insignificant atypia (AUS) or an unexplained follicular lesion (FLUS); (iv) Follicular neoplasm or suspected follicular neoplasm; (V) Suspected of malignancy and (vi) malignant. The information of all patients who entered the study, including age, sex, underlying disease, body mass index, length of hospital stay, type of thyroid pathology, serum calcium levels, phosphorus, PTH before and immediately after surgery, and vitamin D levels before surgery were measured and It was recorded in the pre-prepared information form. The volume of the sample required to evaluate the serum level of vitamin D before surgery with hypocalcemia after thyroidectomy with 95% confidence (significance level 5%) and 90% test power based on the results of Tripathi et al.'s study [11] according to the minimum sampling formula 31 people were estimated in each group.
Data analysis and statistics
The SPSS software version 21.0 was used for data analyses. To describe quantitative variables with normal distribution, mean and standard deviation (about 95% confidence) were used, and for quantitative variables with abnormal distribution, the mean and intermediate-range were used. Qualitative variables were also described based on numbers and percentages. Normal distribution of quantitative study variables was measured using tensile and skew values, and Shapiro-Wilk test. To compare quantitative variables between two groups with and without vitamin D deficiency from the independent t-test; and covariance analysis; ANCOVA was used by modifying the variable effect before surgery. Comparison of quantitative variables before and after thyroidectomy using paired t-test; paired t-test (equivalent to nonparametric Wilcoxon) was used. To compare hypoxia in two groups, the Chi-Square test and, if not validated, the Fisher's Exact Test. Correlation of variables using Pearson correlation coefficient; Pearson correlation (Spearman correlation) was measured.