I am asking this question for a concerned parent of a 13 year old student who has had type�1 diabetes for five months. She takes Lantus occasionally and usually takes Humalog to cover carb intake and treat high blood sugars. The student has been told by her diabetes team that she is experiencing the honeymoon period, but I thought the honeymoon normally exhibited less insulin requirements, some hypoglycemia, etc. On many occasions, she has had blood sugars that drop to the 40s mg/dl [2.2 mmol/L] even with no insulin during the previous 12-24 hours. Her C-peptide level was drawn during a “low”, and it was about “ten times the normal” as reported by her mom. So this proved that it was her own insulin (not injected as thought by diabetes team).

The mom is worried about an insulinoma. Is this possible? What are the tests for it? What else could this student have? The mom is questioning whether she has type 2 diabetes instead, so she is having islet cell antibodies drawn soon.

By far the most probable diagnosis in a 13 year old Caucasian girl presenting with acute insulin dependence would be type�1A (autoimmune) diabetes. Treatment with Lantus (insulin glargine) and Humalog at mealtimes, adjusted for premeal blood sugar and ‘carbs’ consumed, would be entirely orthodox.

Normally nowadays, this would be confirmed by positive antibody tests for one or more of the routine anti-GAD, anti-insulin or ICA512 tests to differentiate it from type�1 diabetes which is antibody negative and where insulin dependence may not be permanent. This latter form of diabetes is uncommon in Caucasian children (about 5%); but constitutes greater than 50% in Hispanic or African Americans.

It is inconceivable that an insulinoma would present with insulin dependence, but it is certainly possible, especially if this girl is overweight (BMI greater than 30 kg body wt/ht. in m2) that she has type�2 diabetes which is becoming increasingly common in this age group. Such a diagnosis could explain a modest rise in serum C-peptide, but not one that is ‘ten times normal’. This result needs to be reviewed with the doctor and the laboratory director to make sure that it is neither a technical error nor one of interpretation. For example, if the result was given in ng/ml and interpreted as though it was nmol/L this mistake could have been made. It should also be confirmed that the sample was a fasting one.

DOB