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October 11, 2003

Blood Tests and Insulin Injections

Question from Pennsylvania, USA:

My 13 year old son was diagnosed with type 1 diabetes five months ago. Can you tell me the purpose and meaning of these tests: insulin antibody, GAD 65 antibody, ICA 512 antibodies, lipoprotein pro, T4, free T4, TSH, C-peptide)? What was measured? What is considered “normal”?


From: DTeam Staff

Diabetes mellitus, especially type 1, is associated with potential complications and other metabolic derangements, especially if attention to control is not good. Such complications and associated conditions include elevations in cholesterol and href=”/dctionary/t.htm#triglycerides”>triglycerides (fat) that increase the risk of heart disease, kidney dysfunction, and visual and nerve damage. In addition, since type 1 diabetes has as its cause a process in which the immune system “fights against itself” (that is to say an “autoimmune disorder”), clinicians will frequently look for other diseases that also have a predilection of autoimmune processes. Typical ones include thyroid diseases, an intestinal disease called celiac disease, and less commonly processes that lead to adrenal gland insufficiency or rheumatoid arthritis, or even lupus.

Therefore, regarding the tests that you inquired about: Insulin antibody, GAD 65 antibody, ICA 512 antibodies are all tests to confirm that the cause of the diabetes is the most common autoimmune disorder. The “normal” levels of antibodies are “none”.

C-peptide is a by-product of the production of insulin and can give a clue as to insulin production. I do not find it commonly helpful in the diagnosis of diabetes, especially type 1. The amount of C-peptide hinges on your blood sugar at the time of the test, in someone without diabetes individual. C-peptide is often increased in people with type 2 diabetes as their bodies do not react to insulin best which leads to a process of excessive insulin production and hence increased C-peptide production.

“Lipoprotein Pro” is a profile of the various proteins and substances that transport cholesterol and fat in the blood. Another way to assess this is to simply measure a fasting lipid profile which measures total cholesterol and the various sub-types of “good” and “bad” cholesterol.

T4, Free T4, and TSH assess thyroid function. T4 is the major form of thyroid hormone. Free T4 is the thyroid hormone that is unattached to blood proteins; therefore it is “free.” Most often there is little reason to do both T4 and Free T4, although in some labs, if your order free T4, they automatically measure the total T4 for comparison. TSH stands for Thyroid Stimulating Hormone and is the hormone the pituitary gland in the brain makes to signal the thyroid gland to make thyroid hormones.