Increases in parathyroid hormone (PTH) after gastric bypass surgery appear to be of a secondary nature.

INTRODUCTION: Endocrine changes, particularly increases in parathyroid hormone (PTH), occurring after gastric bypass procedures have been reported but are not well characterized.

METHODS: We reviewed retrospectively patients who underwent Roux-en-Y (short limb (SL) = 75 cm, long limb (LL) = 165 cm) gastric bypass procedures at our institution from January-December 2005. Patient demographics, laboratory values of serum calcium, Vitamin D, and phosphorous concentrations as well as levels of alkaline phosphate and PTH were followed at quarterly intervals for one year.

RESULTS: 140 patients were identified. Mean age for the group was 45 years and 90% of patients were female. The average BMI was 49.2. The mean PTH levels increased from 29.4 immediately post-op to 43.1 ng/mL (P < .001) one year after surgery. Five percent of the patients had hyperparathyroidism (PTH>53 ng/mL) immediately postoperatively; the ratio then increased to 21% at one year. Only two patients had evidence of true primary hyperparathyroidism with increased PTH and hypercalcemia. Sixty percent of patients had at least a 10 ng/mL increase in PTH level at the end of one year, reflecting a 30% increase from baseline levels. Vitamin D deficiency (levels <20 ng/mL) were identified in 45 patients (32%) initially postoperatively and they continued to be low compared to the rest of the population (P = .004). Vitamin D levels did vary with seasonal sun exposure and were greatest in the third quarter (July-September). Sub-analysis of the group showed that patients with LL gastric bypass had lesser Vitamin D concentrations (22 vs 30 ng/mL, P < .01) compared to SL patients.

CONCLUSION: Although preoperative endocrine abnormalities are present in patients undergoing gastric bypass procedures, the derangements intensify after gastric bypass surgery. A four-fold increase in patients with elevated PTH deserves special attention. When combined with the concurrent prevalence of low serum Vitamin D and normocalcemia in this population, we propose that this is a disorder of secondary hyperparathyroidism requiring medical treatment with Vitamin D supplementation.