Obesity Abstracts

Introduction: It is known that bariatric operations cause nutritional deficiencies especially calcium and vitamin D. Reported hypocalcemia after bariatric surgery ranges from 1% after Roux-en-Y gastric bypass (RYGB) to 25% after bilio-pancreatic diversion-duodenal switch. This is mainly the result of bypassing the preferential sites for calcium and vitamin D absorption. Apart from the bariatric operations, hypocalcemia commonly occurred after total thyroidectomyin 20 percent of patients. Risk of hypocalcemia will increase further after RYGB in history of thyroidectomy, which will make it more difficult to manage.

Case: We are presenting a 49 year-old female with a BMI of 35kg/m² presenting to our clinic for obesity management. She had a previous total thyroidectomy for a compressive goiter 10 years previously, which was complicated by hypoparathyroidism. Which was managed by oral calcium carbonate 1.5 g and alfacalcidol 1mcg bd, with calcium of 2.13 to 2.28 mmol/l. She also had history of connective tissue disease for which she received prednisolone and type 2 diabetes mellitus. She underwent a RYGB in November 2020. Day 1 post-surgery her calcium level was 1.71 mmol/l requiring intravenous replacement in-addition to oral alfacalcidol. She returned 3 months later complaining of paraesthesiae, diarrhoea and a very low calcium of 1.40, phosphate 1.51 mmol/l with parathyroid hormone of 1.2 pmol/l and vitamin D level 79.2 nmol/l. Investigations into her diarrhoea revealed sever bile acid malabsorption for which she was started on colesevelam. She required substantial increases to her alfacalcidol dose (3 mcg bd) before the calcium increased to 1.81 mmol/l.

Conclusion: Our case demonstrates two main factors of post-gastric bypass hypocalcaemia. The main one is malabsorption of oral calcium and vitamin D which normally takesplace in the duodenum and jejunum; bypassing this segment after RYGB and a higher pH contribute to the reduction in absorption. Secondly, severe bile acid malabsorption which presented very soon after her operation, might have further reduced the absorption of vitamin D. To our knowledge our case is the second in the literature presenting RYGB hypocalcemia in a patient with hypoparathyroidism. In such cases higher doses of alfacacidol seem to be necessary to maintain desired calcium concentrations.