The significance of elevated levels of parathyroid hormone in patients with morbid obesity before and after bariatric surgery

Hypothesis: The risk of hyperparathyroidism after the duodenal switch operation is related to the length of the common channel. Design: A retrospective analysis of patients following the duodenal switch operation from October 2, 2000, through February 1, 2002. Setting: Academic tertiary referral hospital. Patients: One hundred sixty-five consecutive patients underwent the duodenal switch operation, performed for morbid obesity, with common channel lengths of 75 cm (n = 103 [group A]) and 100 cm (n = 62 [group B]). Main Outcome Measures: Weight loss and parathyroid hormone, corrected calcium, and 25-hydroxyvitamin D (25-OH D) levels were compared between groups A and B. Values were determined preoperatively, early postoperatively (3-6 months), and late postoperatively (9-18 months). Results: Both groups exhibited a slight reduction in serum calcium concentration, with one quarter decreasing below the normal range. Hyperparathyroidism was more common in group A than group B preoperatively (38.9% vs 14.9%), reflecting the higher body mass index of patients in group A. Hyperparathyroidism was also more frequent in the early (54.9% vs 30.9%) and late (49.4% vs 20.5%) postoperative periods in group A vs group B. New-onset hyperparathyroidism was also more common in group A than group B (42.0% vs 13.3%). After 1 year, subnormal 25-OH D levels were found in 17.0% of the patients in group A and in 10.0% of the patients in group B. Median 25-OH D levels increased in both groups, but tended to be higher in group B. Conclusions: Patients with shorter common channels had a higher risk of developing hyperparathyroidism. This may be related to limited 25-OH D absorption.