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Proceed with caution!
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A woman was referred for fairly urgent consultation by her new primary care physician, whom she had seen only once. The referral was to consider the diagnosis of an insulinoma. The patient had reported a 10-year history of frequent episodes, sometimes several times a day, of hypoglycemia with capillary blood glucose below 50 mg/dL. Her doctor had documented a lab blood glucose of 42 with a corresponding insulin level >250 with a reported normal range of <17. There was no comment about this being a fasting level. A CT scan of the abdomen with attention to the pancreas was reported as normal.
Everything points to this being an insulinoma except:
1: The 10-year history that has defied diagnosis despite visits to many different doctors.
2: Stable body weight over those 10 years — many patients with an insulin secreting tumor and frequent hypoglycemia need to eat often to counteract the symptoms and as a consequence, gain weight.
3: The patient was employed at a hospital with access to insulin — abuse of available medications is regrettably still too frequent in doctors, nurses and other personnel.
The negative CT scan does not enter into this because insulinomas can be quite difficult to detect with imaging procedures.
The extremely high insulin level does not enter into the evaluation either because it was not accompanied by a C-peptide level, a measure of endogenous insulin secretion.
I was falling into the trap of labeling this patient as having self-induced hypoglycemia and was bold enough to directly ask her. She said “no” as expected, but it was not the angry response that I had expected. Time to take a break and discuss the situation with my colleagues in the clinic who, as always, were extremely helpful.
How to proceed? The standard 72-hour fast has become impractical, as admission for that study might not be reimbursable. Fortunately the patient always has symptoms of “hypoglycemia” and has time to always check her CBG before she takes some glucose in order to recover. These episodes happen at home or at work so she has been instructed to go down to the lab and have blood drawn for glucose, insulin and C-peptide before she aborts the symptoms with food. Her willingness to do so further supports the possibility of an insulin secreting tumor. I will keep you posted.