A difficult case of recurrent hypoglycaemia: role of insulin assays in establishing the diagnosis

Background Insulin assays are designed to detect endogenous insulin, however, insulin assays produced by different manufacturers may detect exogenous recombinant insulin, with varying degrees of cross‐reactivity between different assays. We report a fascinating and difficult case of recurrent hypoglycaemia, where the final diagnosis was established with the help of insulin assays using different platforms. Case Report A 24‐year‐old female presented with recurrent hypoglycaemic episodes on a background of Type 1 diabetes mellitus and a completely resected synovial sarcoma of the right hip several years previously. She reported significant physical, sexual and emotional abuse leading to reduced appetite and weight loss. Despite withdrawing insulin therapy, she experienced profound hypoglycaemic episodes with detectable C‐peptide and inappropriately elevated insulin levels, suggesting endogenous hyperinsulinaemic hypoglycaemia; however, localization studies were negative and finally she was found to have exogenous hyperinsulinaemia after discordant insulin levels were detected using two different insulin assays. The C‐peptide level was elevated as a result of stimulation by parenteral dextrose and was suppressed after dextrose was ceased. Her Type 1 diabetes mellitus was fabricated and she had factitious hypoglycaemia. Conclusions Factitious hypoglycemia is difficult to diagnose and treat. A low blood glucose level, suppressed C‐peptide level and an inappropriately elevated insulin level is the classic finding. We were able to make a diagnosis in the present case after discordant insulin levels were detected on the two different insulin assays, signifying cross‐reactivities of the recombinant insulin with the assays. A multidisciplinary team approach with psychiatric input is needed to treat such cases.