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From Atlanta, Georgia, USA:

What is the name of the test used to discriminate between Type 1 and Type 2? I have a friend who has had diabetes from age 22 and is now 46. She uses a pump for her insulin. She weighs 176 pounds, stands about 5 feet, 4 inches (she is on a diet). Her doctor (after weight loss of 25 pounds) thinks that maybe she was misdiagnosed. Is this possible? Will the test show at this time which she is? I'm confused. Was the test available then?

I'm a nurse but this one is strange to me. I thought once a Type 1, always a Type 1.


At this stage it might be a rather cumbersome and costly business to try to distinguish between Type 1 and Type 2 Diabetes. A test for C-peptide in serum would be the easiest way. If this residual fragment of proinsulin were present it would indicate some form of Type 2 Diabetes.

The usual laboratory confirmation of Type 1 or autoimmune diabetes are certain antibodies in serum. However at this stage these may no longer be present although it would still be possible to define your friends genetic make-up in terms of HLA antigens. If one of the two 'high susceptibility' variants were present that would infer Type 1 Diabetes even with a negative antibody test.

Specific tests for Type 2 Diabetes are rather in a state of flux at the moment. The reason is that in the last few years geneticists have begun defining an increasing number of subsets of Type 2 that are genetically distinct. These include conditions like mitochondrial diabetes, insulin resistant syndromes, several types of maturity onset diabetes in the young (MODY), amylin deficiency and so on. These are for the most part clinically alike and amenable to the same treatment, so that there is little pressure for an exact laboratory diagnosis. In your friend's case meticulous control is more important than any thing else, however if some of her own insulin can be shown by the C-peptide test it might be worth discussing with her doctor the possibility of a trial of one of the new oral medications such as troglitazone. The prospect of being able to come off insulin in these circumstances is only about 25% though. Finally if your friend had a strong family history of diabetes at the time of onset or was overweight this would favour Type 2.


Original posting 14 Nov 97


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