Endocrine Abstracts

Case history: A 54 year-old gentleman was transferred as an inpatient from another centre for investigation and management of refractory hypoglycaemia following a revision gastric bypass. He was requiring a continuous infusion of 20% dextrose on transfer to maintain normoglycaemia. He had a complex bariatric surgical history dating back 7 years. His initial procedure had been a sleeve gastrectomy that was subsequently converted to a gastric bypass which had then been reversed prior to this most recent operation. He had been particularly troubled by acid reflux, requiring multiple OGDs and dilatations of the gastro-oesophageal junction. He had long-standing symptoms suggestive of hypoglycaemia that developed approximately 2 years after his bypass, which had been investigated on a number of previous occasions. Results had been consistent with endogenous hyperinsulinaemic hypoglycaemia (detectable insulin and c-peptide), in keeping with dysregulated glucose regulation post bariatric surgery. Dietary and medical interventions had been of limited success.

Results and treatment: Initial management was with a phased reduction of IV dextrose infusion with the addition of diazoxide and octreotide that, over a number of days, reduced the frequency and severity of hypoglycaemia. Laboratory hypoglycaemia (glucose <2.2 mmol/l) was confirmed at both the referring hospital and our centre. During these episodes, plasma insulin was undetectable when using the Roche assay (which does not cross-react with exogenous insulin), but elevated when measured on the Mercodia platform (which does). Corresponding c-peptide concentrations were low in all instances. A urine sulphonylurea screen and insulin antibodies were negative. These results were consistent with exogenous insulin administration and he was discharged following input from the psychiatry service. He has attended post discharge follow up and reported a reduction in instances of hypoglycaemia at home, which were no longer interfering with his life.

Conclusions and points for discussion: Endogenous hyperinsulinaemic hypoglycaemia is a rare but well recognised and significant complication of gastric bypass surgery. Exogenous insulin administration is an important cause of hypoglycaemia and requires a high threshold of suspicion to detect. The co-existence of both is highly unusual and this case provides an excellent opportunity to discuss:

• The biochemical assessment of insulin and c-peptide during hypoglycaemia

• Differences in cross-reactivity in commonly used assays and the importance of close collaboration with the Biochemistry department

• Appropriate re-evaluation of an existing diagnosis when the clinical situation changes or treatment response is not as expected