Risk Factors for Secondary Hyperparathyroidism after Bariatric Surgery: A Comparison of 4 Different Operations and of Vitamin D-receptor-polymorphism

Abstract

To determine the relative frequency of secondary hyperparathyroidism after 1 of 4 standard bariatric surgical procedures, with respect to vitamin D-receptor (VDR) Bsm1 genotype-polymorphism (VDRP). Included were 141 obese men and women [aged 44.6±10.4 years, body mass index (BMI) 44.4±5.4 kg/m²], who had undergone either gastric banding (GB; n = 39), laparoscopic sleeve-gastrectomy (LSG; n = 31), Roux-en-Y-gastric-bypass (RYGB; n=43), or biliopancreatic-diversion with "duodenal switch" (BP-DS; n = 28)]. They were tested for VDR-genotype (Bsm1), vitamin D, and serum-PTH-levels postoperatively. Analysis of Covariance revealed a treatment effect, showing statistically significantly higher PTH-levels after BP-DS than after GB (mean difference = 32.14, p<0.001), after SG (mean difference = 25.18, p=0.001), or after RYGB (mean difference = 18.15, p=0.020). VDR-BSM1-genotype did not influence PTH-levels and vitamin-D postoperatively. Logistic regression indicated that the risk of developing SHPT after BP-DS was 12.5 times higher than after GB and 16.7 times higher than after SG. Beside other variables, VDR-genotype and the interaction between VDR-genotype and type of surgery did not attain statistical significance. In a comparison of the 4 most frequently performed bariatric operations vitamin-D-receptor polymorphism (VDRP) had no influence on the development of postoperative secondary hyperparathyroidism (SHPT) and is not useful as a predictor. SHPT occurs most often after BP-DS. Operation type, gender, VDRP, preoperative BMI, and relative postoperative BMI-loss, however, only explain 24% of the variance in postoperative PTH levels. Other gastral or intestinal factors physiologically promoting calcium-turnover and PTH regulation are postulated.