Aim: To evaluate the influence of age of onset and duration of diabetes on the positivity of glutamic acid decarboxylase antibody (GADA) in South-Brazilian type 1 diabetes mellitus (DM) patients.
Methods: GADA was evaluated in 92 patients with type 1 diabetes, in 147 gestational DM patients, and in 59 subjects with normal glucose tolerance.
Results: Type 1 patients with positive GADA (N = 44, 48%) were older at the onset of diabetes (22 ± 9 versus 18 ± 10 y, P = 0.043) and had a shorter DM duration (12 ± 8 versus 19 ± 9 y, P < 0.001), as compared with negative GADA patients. A logistic regression with antibody positivity as the dependent variable and diabetes duration as the independent variable, showed that the shorter diabetes duration was related to the presence of the antibody with an odds ratio (OR) = 5.6; (CI 95% = 2.1-14.6); P < 0.001. Another model, with age at diagnosis as the independent variable, did not show any association with antibody positivity. However, analysing only men, a shorter DM duration (OR = 6.5; CI = 1.7-24.0; P = 0.006), and also a higher age at diagnosis (OR = 5.5; CI = 1.5-21.0; P = 0.01) were significantly related to the antibody positivity. The performance of GADA was similar in up to 15 y of duration of DM (P = 0.78), but significantly diminished with higher duration (P = 0.001).
Conclusion: GADA testing is a helpful tool in the diagnosis of type 1 DM starting in young adults and older individuals. Even though the positivity rate declines along the course of disease, it still provides useful information up to 15 y after the diabetes diagnosis.