I do not have diabetes, but I am being investigated for hypoglycemia. I’ve have had quite a few fasting low blood sugar levels, sometimes as low as 2.5 mmol/L [45 mg/dl]. Also, if I follow a hypoglycemic diet either with eating high protein/no carbohydrate diet or low Glycemic Index (GI) carbohydrates I go low, too. But, I think some of it may be mild reactive hypoglycemia, too. I get a bit of a spike in my blood sugar level after meals like low GI bread or pasta, going up to 9 to 10 mmol/L [162 to 180 mg/dl], but, within four hours, I am back to around 4 mmol/L [72 mg/dl] to 5 mmol/L [90 mg/d]. I also go low with exercise, normally less than 3.5 mmol/L [63 mg/dl].

I had a C-Peptide done with was 0.67 nmol/l (reference range 0.40 nmol/L to 1.70 nmol/L). I’ve heard that people with type 1 diabetes tend to have fasting C-Peptide concentrations less than 1.0 nmol/L and often less than 0.5 nmol/L. I thought 0.67 was a bit high for me. I am 157 cm (5 feet, 1 inch) and weight 44 kilos (97 pounds). My serum insulin was 9 mIU/L. Both the C-Peptide and insulin level were non-fasting numbers. My doctor said the insulin level was high. What does all this mean?

I need to have some other tests done, including those for my cortisol level and insulin antibodies, LFTs (liver function), UEC (Urea, Electrolytes, Creatinine (renal function blood test)). What is an insulin antibody?

Hypoglycemia is difficult to investigate because there are no clear lines of demarcation, in terms of values that make the diagnosis. Only when it jumps out at you that the insulin and C-Peptide values are very high when the glucose is low is the diagnosis easy to make. Hypoglycemia is usually divided into fasting hypoglycemia and reactive hypoglycemia (reactive in the sense that it is in response to a meal). The C-Peptide is always measured in relation to the glucose. The total insulin is also obtained. Your studies were done non-fasting. It makes it more difficult to say that the insulin levels were “high” at 9 when they were not fasting. The other condition where C-Peptide, insulin, and glucose are measured is in the setting of a 72 hour fast. Patients are asked not to eat for a prolonged period in order to diagnose whether the low blood sugars are the result of an insulin-producing tumor called an insulinoma. In this situation, patients wait for the blood sugar to drop to values that are symptomatic, usually less than 2.2 mmol/l [40 mg/dl]. When the C-Peptide is measured during low periods, if it is inappropriately elevated, that helps to make the diagnosis of the insulinoma.

Insulin antibodies are measured for several reasons. Sometimes patients have high levels of insulin antibodies that circulate in the blood. They serve as a reservoir for binding up insulin and then, all at once, the insulin can be released in a non-physiologic manner and cause low blood sugars. There is also an even rarer syndrome associated with antibodies that bind to the receptor for insulin and give insulin-like effects. Fortunately, all these are very rare. Statistically, you are still most likely to have a reactive component to hypoglycemia. You need to work closely with your physician to find the underlying cause.

JTL