The C-Peptide test measures how much insulin is released from the pancreas, when stimulated by glucose to do so.According to Mosby�s Manual of Diagnostic and Laboratory Tests � Second Edition, �The exogenously administered insulin suppresses endogenous insulin production.�More accurately, exogenous insulin controls blood glucose concentrations, thus preventing stimulation of endogenous insulin release, which may in effect suppress endogenous insulin production. The C-Peptide test does not indicate whether the beta islet cells of the pancreas are working or not, nor whether there are in fact beta cells present.C-Peptide is not a test for insulin production, but a test for insulin released from the pancreas. To understand how the pancreatic beta cells are working one needs to look at the C-Peptide test and at the blood glucose level at the time of test, and consider all the factors that I have previously listed that contribute to hyperglycemia, to arrive at an objective conclusion. As a blood glucose load increases, the C-Peptide levels increase. Of course insulin users (type 1) with good blood glucose control are C-Peptide negative or of low value, let me explain: A child has a cold-like infection and his blood glucose levels increase to astronomical heights (lets say 500 mg/dl).This is considered an emergency situation (because of ketoacidosis).So after a quick finger test in the emergency room the patient is put on insulin (intravenously) according to standard procedures. The high blood glucose levels, caused by infection, are lowered to normal levels again with exogenous insulin.The child is told not to eat.6-10 hours pass and finally an endocrinologist comes around to examine the patient, then he orders a C-Peptide test.And of course it comes back negative or have low value:confirming type 1 diabetes. This is a false conclusion because the exogenous insulin is controlling the blood glucose and the child has not eaten in 6-10 hours so there is no new glucose entering the blood stream through the intestines.The pancreas has no reason to release insulin (measured by the C-Peptide test).Hence, the result is C-Peptide negative or of low value. Insulin pump users with good blood glucose control will also have these same misinterpreted results. The only way for insulin using diabetics to prove in spite of poor or of good blood glucose control and also of the Glycohemoglobin or Hemoglobin A1c test (HbA1c - a test for average long term blood glucose, about three months) that they have in fact Type 2 Diabetes which is a curable condition, and not Type 1 Diabetes, is to stimulate the pancreas to release insulin before taking the C-Peptide test. Increase the blood glucose above normal for at least one hour before taking the blood test. This should help exculpate the pancreas and prove that maybe the beta cells are there and functioning normally, proving type 2. I have done the C-Peptide test recently; it was 6.2 nanograms per milliliter (ng/ml). -- This is above normal, and proves type 2.My blood glucose at the time of the C-Peptide test was about 230 mg/dl (not intentionally). -- I credit this fact for giving me the result that convinced my doctor that I was really a type 2 diabetic. I was using 70 units of Lantus� 24 hour basal insulin a day and my pancreas was also releasing insulin above the normal range. This was evidence that there was a very heavy glucose load present.Since I was on a no carbohydrate, low calorie diet and my basal insulin was dosed correctly, the heavy glucose load was an unexplainable factor.The sudden need to drop the amount of insulin that I was using right after starting on antibiotics proved that this very heavy glucose load was due in fact to an infection. The C-Peptide test was done first; the antibiotics were started a week later after the nasal and sinus symptoms came out. According to Mosby's Manual of Diagnostic and Laboratory Tests - Second Edition 2002 by Kathleen Deska Pagana, Ph.D., RN & Timothy J. Pagana, MD,FACS - Pages 186-188 Mosby�s Inc. � St. Louis, MO USA ISBN 0-323-01609-X �Fasting range is: 0.78 - 1.89 ng/ml (0.26 - 0.62 nmol/L SI unit) Range one hour after a glucose load is: 5.00 -12.00 ng/ml� (During a glucose tolerance test) According to my lab report, the normal reference range is 0.6 - 3.2 ng/ml.This reference range may be misleading for doctors because it is incomplete. I conclude that the complete human C-Peptide range as opposed to the "normal" range is in fact 0.6 - 12.0 ng/ml, keep in mind that the normal values are for a non-diabetic person. The values will be lower in an insulin user and higher in a type 2 oral agent user (agents that promote the release of insulin from the pancreas) when blood glucose levels are controlled. The C-Peptide test is mostly used to diagnose and evaluate patients who are hypoglycemic (produce too much insulin) as well as those who have insulinomas (insulin producing tumors).The test is also used to see if a normal person is secretly using insulin. They may ask patients to fast for this test (to reduce glucose levels in the blood) to establish a baseline in hypoglycemia cases.This is currently a standard procedure for this test. In diabetics however the baseline has to be the opposite, to increase glucose levels in the blood, in order to prove type 2.Fasting may not yield the intended results.Do not fast. What I understand from these two sources about my own condition is that if I were normal, non-diabetic, these results would mean that my pancreas releases insulin above the normal reference range.However, I have a low glucose tolerance threshold. My 6.2 ng/ml C-Peptide falls at the bottom of the 5-12 ng/ml glucose test range. I can only presume that people who can tolerate a high carbohydrate diet would have scored a 12 ng/ml on the C-Peptide test for glucose tolerance.Perhaps because they have a higher genetic glucose tolerance (more beta islet cells), and the blood sugars are better controlled under extreme conditions such as infection and poor diet, they may in effect have better immunity against disease. The values of the C-Peptide test and blood glucose separately do not give an absolute picture of what is actually happening, they must be considered together.Even when they are considered together they still may not present a complete picture of the diabetic condition.Let me add one more factor to the picture, which may be relevant: The metabolic rate as controlled by the thyroid gland, which is different in each person. As I use less exogenous insulin, and more of my own natural insulin I feel a positive change in my mood that has been absent for a long time.I attribute this to the fact that more C-peptide is now being released along with insulin from my pancreas.Perhaps C-peptide has a physiological effect on mood.Bottled insulin does not contain C-Peptide and using it suppresses natural insulin release and probably C-Peptide that is released with it.This may explain why I have noticed that my mood was great, even thought I had high blood glucose at times and a dull mood when having normal glucose levels controlled by bottled insulin.The fact that an insulin dependent diabetic feels good after eating a meal may be proof that there is endogenous insulin release, because C-Peptide is also being released. On the subject of diagnostic tests, I found that Mosby's manual contains more complete information about the C-Peptide test than other sources that I looked up. < PREVHOMENEXT >