I have been experiencing low blood sugar (in the 40's) after eating breakfast. My doctor recently ordered a fasting insulin and C-Peptide. The results were: insulin 35 uIU/ml (normal is under 17). C-Peptide was 4 ng/ml (normal is .8-3.1). My random glucose was 64. The doctor referred me to an endocrinologist, who said that I didn't meet the criteria to be seen...no explanation. I read online that high insulin and C-Peptide, and low blood glucose could indicate a tumor on the pancreas (insulinoma). Does any one have additional information or advise?