Anti-GAD-positive patients with type 1 diabetes mellitus have higher prevalence of autoimmune thyroiditis than anti-GAD-negative patients with type 1 and type 2 diabetes mellitus.

The aim of our study was to evaluate antibodies against thyroglobulin (anti-TG) and thyroid peroxidase (anti-TPO) - markers of autoimmune thyroiditis - in several groups of adult patients with type 1 and type 2 diabetes mellitus (DM). We were particularly interested whether the presence of thyroid antibodies is related to the positivity of glutamic acid decarboxylase antibodies (anti-GAD). We found elevated anti-GAD in 46 % (97/210) patients with type 1 DM. All patients with type 2 diabetes were anti-GAD-negative. At least one thyroid antibody (anti-TG and/or anti-TPO) was found in 30 % (62/210) patients with type 1 DM and 27 % (22/83) type 2 diabetes patients. The patients with type 1 DM were further grouped according to their anti-GAD status. The anti-GAD-positive patients had a higher prevalence of anti-TG antibodies than the anti-GAD-negative patients (25 % vs. 12 %, p=0.03) as well as anti-TPO antibodies (32 % vs. 12 %, p<0.001). At least one thyroid antibody was detected in 39 % (38/97) of anti-GAD-positive but only in 21 % (24/113) of anti-GAD-negative patients with type 1 DM (p=0.006). No significant difference in the frequency of thyroid antibodies was found between anti-GAD-negative patients with type 1 and type 2 DM (21 % vs. 27 %, p=0.4). The groups with or without thyroid antibodies in both type 1 and type 2 diabetic patients did not differ in actual age, the age at diabetes onset, duration of diabetes, body mass index or HbA1c level. Patients with elevated thyroid antibodies had significantly higher levels of TSH than those without thyroid antibodies (1.86 vs. 3.22 mIU/l, p=0.04 in type 1 DM; 2.06 vs. 4.89 mIU/l, p=0.003 in type 2 DM). We conclude that there is a higher frequency of thyroid-specific antibodies in anti-GAD-positive adult patients with type 1 DM than in anti-GAD-negative patients or in patients with type 2 DM. Patients with or without thyroid antibodies do not differ in age, DM onset and duration, BMI or HbA1c. Thyroid antibodies-positive patients have higher levels of thyroid stimulating hormone (TSH).

[C-peptide as the decisive factor for classification of type 1 diabetes mellitus and type 2 diabetes mellitus]. / C-peptid jako rozhodující faktor pro klasifikaci diabetu mellitu 1. typu a diabetu mellitu 2. typu.

OBJECTIVE: The main objective was to seek, based on defined groups of diabetics, C-peptide levels on fasting and after stimulation which would help to differentiate diabetes mellitus type 1 from diabetes mellitus type 2 in patients with manifestation of diabetes in adult age. GROUPS: Group A comprised 65 non-obese diabetics type 2 with failure of PAD treatment. Group B included 304 newly manifested diabetics type 1 and 2 aged 31-65 years. Group C was formed by 424 patients with diabetes mellitus type 1 and type 2 with different duration of diabetes. RESULTS: Group A: mean C-peptide levels on fasting 0.32 and after stimulation with a standard breakfast 0.59 pmol/ml suggest absolute insulin deficiency in type 2 diabetics with failure of PAD treatment. Group B: 29.2% diabetics type 1 had already during manifestation of diabetes C-peptide levels on fasting < 0.43 pmol/ml and 47.9% C-peptide of < 0.6 after a meal. There were 1.9 and 4.9% subjects among type 2 diabetics with such low C-peptide levels. After a six-year follow up the mean C-peptide levels on fasting declined in type 1 diabetics from 0.49 to 0.16 pmol/ml and in patients originally with type 2 diabetes reclassified to type 1 the levels dropped from 0.56 to 0.26 pmol/ml. Group C served as the basic group for statistically (linear regression method) detected discrimination values of C-peptide differentiating diabetes mellitus type 1 and diabetes mellitus type 2--the liminal value being 0.59 pmol/ml on fasting and 1.0 pmol/ml after a meal. CONCLUSION: In clinical practice it is not possible to assess reliably slowly manifesting diabetes type 1 (LADA by age, BMI and compensation of diabetes. Positivity of antiGAD antibodies does not rule out diabetes mellitus type 1. In unequivocal cases the decisive factor is therefore the C-peptide level on fasting and after a meal.