{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,8,20]],"date-time":"2026-08-20T14:32:50Z","timestamp":1787236370684,"version":"build-2736575974"},"reference-count":14,"publisher":"BMJ","issue":"8","content-domain":{"domain":["bmj.com"],"crossmark-restriction":true},"short-container-title":["BMJ Case Rep"],"accepted":{"date-parts":[[2026,8,8]]},"published-print":{"date-parts":[[2026,8]]},"abstract":"<jats:p>Insulin autoimmune syndrome (IAS) is a rare cause of spontaneous endogenous hyperinsulinaemic hypoglycaemia, mediated by autoantibodies directed against endogenous insulin in the absence of prior exposure to exogenous insulin. An elderly woman presented with recurrent episodes of both fasting and postprandial hypoglycaemia in the absence of diabetes mellitus or prior bariatric surgery. Whipple\u2019s triad was fulfilled, and during documented hypoglycaemia (plasma glucose 2.4 mmol\/L), insulin and C-peptide concentrations were markedly elevated, with a negative sulfonylurea screen. A 72-hour supervised fast and a mixed-meal test demonstrated early-onset hypoglycaemia accompanied by elevated insulin and C-peptide levels. Cross-sectional and functional imaging revealed no pancreatic lesion. Insulin IgG antibodies were strongly positive and polyethylene glycol precipitation confirmed significant assay interference, supporting the diagnosis of IAS. This case highlights the diagnostic challenges and clinical course of this rare condition.<\/jats:p>","DOI":"10.1136\/bcr-2026-272400","type":"journal-article","created":{"date-parts":[[2026,8,20]],"date-time":"2026-08-20T13:25:24Z","timestamp":1787232324000},"page":"e272400","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":0,"title":["Diagnostic pitfalls in endogenous hyperinsulinaemic hypoglycaemia due to insulin autoimmune syndrome"],"prefix":"10.1136","volume":"19","author":[{"ORCID":"https:\/\/orcid.org\/0009-0004-8783-0900","authenticated-orcid":false,"given":"Abdul","family":"Wahab","sequence":"first","affiliation":[{"name":"Acute Medical Unit, West Middlesex University Hospital, Isleworth, UK"},{"name":"Chelsea and Westminster Hospital NHS Foundation Trust, London, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Muhammad Zahir","family":"Shah","sequence":"additional","affiliation":[{"name":"Endocrinology, Princess Alexandra Hospital NHS Trust, Harlow, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0001-8877-7492","authenticated-orcid":false,"given":"Nadia","family":"Ijaz","sequence":"additional","affiliation":[{"name":"Endocrinology, West Middlesex University Hospital, Isleworth, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"239","published-online":{"date-parts":[[2026,8,20]]},"reference":[{"key":"2026082006251202000_19.8.e272400.1","first-page":"312","article-title":"Insulin autoimmunity in a case of spontaneous hypoglycaemia","volume":"13","author":"Hirata","year":"1970","journal-title":"J Jpn Diabetes Soc"},{"key":"2026082006251202000_19.8.e272400.2","article-title":"Rare Cause of Recurrent Hypoglycemia: Insulin Autoimmune Syndrome","volume":"2017","author":"Tinmanee","year":"2017","journal-title":"Case Rep Endocrinol"},{"key":"2026082006251202000_19.8.e272400.3","first-page":"e35","article-title":"Glucose changes in a patient with insulin autoimmune syndrome demonstrated by continuous glucose monitoring","volume":"5","author":"Lin","year":"2019","journal-title":"AACE Clin Case Rep"},{"key":"2026082006251202000_19.8.e272400.4","doi-asserted-by":"publisher","DOI":"10.1016\/j.diabres.2008.10.015"},{"key":"2026082006251202000_19.8.e272400.5","doi-asserted-by":"crossref","DOI":"10.5041\/RMMJ.10212","article-title":"Unusual Manifestations of Essential Monoclonal Gammopathy. 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