SAT-562 - Unmasking Factitious Hypoglycemia: The Role of Insulin Analogue Assays

Introduction

Non-diabetic hypoglycemia requires accurate diagnosis to guide treatment. Causes include insulinoma, adrenal insufficiency, post-bariatric hypoglycemia, and rarely surreptitious insulin use. We present a case of factitious hypoglycemia confirmed via insulin analog testing.

Case Presentation

A 49-year-old woman with a history of Roux-en-Y gastric bypass (2017), psychogenic nonepileptic seizures, and mood disorder presented with symptomatic hypoglycemia (glucose 45 mg/dL). Her CGM showed rapid post-prandial fluctuations, which along with her history suggested post-bariatric hypoglycemia. However, treatment with dietary modification, acarbose, and diazoxide yielded no improvement, leading to recurrent hospitalizations.

Inpatient evaluations showed normal glucose levels, with events occurring only when unobserved. Biochemical testing during hypoglycemia revealed inappropriately low insulin and C-peptide. ACTH stimulation testing, abdominal CT, and mixed meal tolerance test were unremarkable.

During an outpatient follow-up, a witnessed severe hypoglycemic episode occurred. Given the atypical biochemical profile and psychiatric history, testing for exogenous insulin was performed. Results showed marked hypoglycemia with suppressed endogenous insulin/C-peptide and a negative sulfonylurea screen. Insulin analog testing via LC-MS (ARUP/Mayo Clinic) detected markedly elevated insulin analog levels, confirming exogenous exposure. When confronted, the patient admitted to "mistakenly" injecting her mother’s insulin. Hypoglycemia resolved post-disclosure.

Discussion
Surreptitious insulin use is a form of factitious disorder (Munchausen syndrome). Our patient’s case—self-administration without external gain, LC-MS confirmation, and resolution after disclosure—fits this diagnosis. Factitious hypoglycemia is life-threatening due to neuroglycopenia risks. Traditional immunoassays often fail to detect insulin analogs due to very high specificity and limited cross-reactivity. In high-suspicion cases, LC-MS/MS is crucial as it identifies specific insulin species by mass-to-charge ratios, bypassing the limitations of standard assays.

Conclusion

Surreptitious insulin use is a rare but critical differential in non-diabetic hypoglycemia. A high degree of suspicion and specialized insulin analog assays are necessary for diagnosis, particularly in patients with psychiatric comorbidities

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