ORIGINAL CONTRIBUTION Secondary Hyperparathyroidism in Patients with Biliopancreatic Diversion After 10 Years of Follow-up, and Relationship with Vitamin D and Serum Calcium Mirian Alejo Ramos 1 & Isidoro M. Cano Rodríguez 1 & Ana M. Urioste Fondo 1 & Begoña Pintor de la Maza 1 & David E. Barajas Galindo 1 & Paula Fernández Martínez 1 & Luis González Herráez 2 & Tomás González de Francisco 2 & María D. Ballesteros Pomar 1 # Springer Science+Business Media, LLC, part of Springer Nature 2018 Abstract Background Secondary hyperparathyroidism (SHPT) is a matter of concern after biliopancreatic diversion (BPD). The aim of this study was to investigate the relationship between SHPT, 25(OH)D, and calcium after BPD. Design A retrospective analysis in obese patients after BPD performed between 1998 and 2016. Methods Patients with at least 1 year of follow-up were included. SHPT was considered when PTH > 65 pg/mL in the absence of an elevated corrected calcium. 25(OH)D (ng/mL) status was defined as: deficiency < 20, insufficiency 20–29.9, and sufficiency ≥ 30. Results In total, 321 patients were included (76.6% women), with mean age 43.0 (10.5) years. Median follow-up was 6.0 (IQR 3.0–9.0) years. Mean body mass index was 49.8 (7.0) kg/m 2 . SHPT increased to a maximum of 81.9% in the ninth year of follow- up (95% CI: 1.5–9.1). Two years after surgery, 33.9% of patients with 25(OH)D sufficiency had SHPT (p = 0.001). Corrected calcium levels were lower in patients with PTH > 65 pg/mL when compared with PTH < 65 pg/mL; 1 year: 8.96 vs 9.1 mg/dL and 5 years: 8.75 vs 9.12 mg/dL (p < 0.01). After surgery, patients with PTH > 65 pg/mL and 25(OH)D sufficiency had lower corrected calcium levels when compared with subjects with PTH and 25(OH)D in normal range. Two years: 9.0 vs 9.2 mg/dL (p < 0.05) and 4 years: 8.9 vs 9.2 mg/dL (p < 0.01). Conclusions Once 25(OH)D is sufficient, the increase in PTH persists associated with a decrease in serum corrected calcium. It is important to ensure a sufficient calcium intake in these patients in order to avoid SHPT and osteomalacia in the future. Keywords Bariatric surgery . Biliopancreatic diversion . Hyperparathyroidism . Serum calcium . Parathyroid hormone . Vitamin D Introduction Over the past decades, obesity has become a worldwide health issue, with an increase in its prevalence and impact [1–3]. Although bariatric surgery (BS) is an effective intervention for the treatment of obesity, it is not risk-free, as one of its complications is the alteration of phosphate-calcium metabolism, especially in the malabsorptive surgical techniques [4]. Within these alterations, we can find a high prevalence of secondary hyperparathyroidism (SHPT) and vitamin D deficiency [5]. Calcium and vitamin D malabsorption are common after mixed or malabsorptive BS, and it is persistent despite oral supplementation. This malabsorption leads to a maintained increase of parathyroid hormone (PTH), triggering a negative effect on bone metabolism [6–8]. Given the important role of vitamin D in calcium absorption, low levels can exacerbate calcium malabsorption and consequently instigate a reduction in serum ionic calcium with subsequent stimulation of PTH synthesis and release [9]. Newbury et al. [8] studied calcium and PTH evolution in 82 patients undergoing biliopancreatic diversion (BPD), not- ing that 25.9% of patients had hypocalcemia between the * Mirian Alejo Ramos mirian_alejo@hotmail.com 1 Department of Endocrinology and Nutrition, Complejo Asistencial Universitario de León, Altos de Nava s/n, Edificio Administrativo Ala Sur, 2ª planta, 24008 León, Spain 2 Department of General Surgery, Complejo Asistencial Universitario de León, Altos de Nava s/n, Edificio Administrativo Ala Sur, 2ª planta, 24008 León, Spain Obesity Surgery https://doi.org/10.1007/s11695-018-03624-3