August 20, 2000
Diagnosis and Symptoms
Question from Lyndhurst, New Jersey, USA:
Can you please explain my son's test results? He was diagnosed with type 1 diabetes a year ago. He was 13 years old at the time and was 15 pounds overweight. Here are the results when first diagnosed: Thyroglobulin Autoantibodies: Result <1_10 (Reference Range <1_10 titer), Thyroid Peroxidase Autoantibodies: Result <35 (Reference Range <35IU/ml), Insulin: Result 5.0 (Reference Range <22.7uU/ml), Islet Cell Autoantibodies CF: Result 1:2 (Reference Range <1_1 titer), Islet Cell IgG Autoantibodies: Result 20 (Reference Range <5 JDF Units), C-Peptide: Result 1.6 ng/ml (Reference Range 0.5-2.0). His last three HbA1C's have been 5.8, 6.0, and 6.5%. His insulin injections consist of 10 units NPH and 2 units Humalog before breakfast, 2 units of Humalog before dinner, and 4 units of NPH before bed.
It is always difficult to comment on a single set of laboratory results, especially when you know nothing of the reasons for the test, the circumstances in which samples were obtained (e.g., fasting or not), and the precise methodology which may vary a lot from lab to lab. For this reason, you should be sure to share any comments here with your son’s diabetes doctor.
As I interpret the story, your son has now been diagnosed for about 10 months and is still on a dose of insulin that looks as though it’s somewhat less than half the usual amount at this stage. I imagine his doctor asked for all these tests to try to determine whether your son had one of three kinds of diabetes. The most common would be Type�1A or autoimmune diabetes. The next would be Type�1B diabetes. Finally, there is the possibility of Type 2 diabetes.
The negative thyroid tests simply mean that, at this time, there is no evidence of hypothyroidism which is another autoimmune condition that often accompanies Type 1A diabetes. It does not mean that he does not have Type IA diabetes. The positive islet cell antibody test would seem to confirm the Type IA diagnosis and therefore a need for insulin in the foreseeable future, but there is a huge variability in the way this is test is done and this is why, in most centers, it is now usual to test for three separate antibodies, anti GAD65 (glutamic acid decarboxylase), anti-insulin antibodies (IAA) and ICA512, a refinement of the older ICA tests. I would ask the doctor to consider repeating an expanded antibody test to make absolutely sure of the Type IA diagnosis. If the repeat antibody test turns out to be negative however, then it might be that your son has Type 1B diabetes. This is a variety that occurs in about 50% of Hispanic new onset families. The underlying pathology is not yet well understood, but it is important to recognise because about half these cases can be managed without insulin, at least for a number of years and blood sugars can be controlled with diet, exercise and sometimes oral medication. Type 2 diabetes is increasingly common in children, especially if there is a family history and if the individual is overweight. The C-peptide test is usually normal or elevated, and, in your son’s case, it appears to be within normal limits and the same is true for insulin levels which here seem to be inconsistently low. However, both these levels are enormously dependent on the time the sample is taken in relation to a meal. The body weight issue also needs to further resolved more specifically by looking at his weight before diagnosis in relation to his height.
Since Type IB and Type 2 diabetes can be managed without insulin, I think it would be worth pressing for the repeat of an expanded antibody test to make quite sure a diagnosis of the insulin dependent Type IA is correct. If, and I think that this is unlikely, the repeat antibody test is negative, then it would be important to also repeat the C-peptide test under clearly defined conditions in order to differentiate Type 2 from Type IB because the treatment and prognosis of these two conditions can be different.