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Latent autoimmune diabetes in adults (LADA) is characterized by a relatively mild diabetes onset, autoantibody positivity, and eventual requirement for insulin therapy. Glutamic acid decarboxylase autoantibodies (GADA) or cytoplasmic islet cell autoantibodies (ICA) play a key role in distinguishing LADA from type 2 diabetes mellitus (T2DM) in clinical practice. The aim of our research was to determine whether insulin autoantibody (IAA) has some additional value in diagnosing LADA. We analyzed IAA, GADA, and IA-2A (antibodies to insulinoma-associated antigen-2) in 1,003 newly diagnosed phenotypic T2DM patients, 110 type 1 diabetes mellitus (T1DM) patients, and 317 normal controls to survey the prevalence of IAA in phenotypic T2DM patients and the overlapping positivity of IAA with other autoantibodies. Sera were drawn within 7 days from the start of insulin therapy. Results showed that 3.39% of the newly diagnosed phenotypic T2DM, 0.95% of normal control (χ = 5.3, P < 0.05), and 21.82% of T1DM (χ = 68.2, P < 0.001) were positive for IAA at diagnosis. The combination frequency of three antibodies was 10.47%, which was higher than any single antibody testing. Combination testing of IAA with GADA and IA-2A could improve LADA diagnose rate by 2.39% than that of GADA and IA-2A. IAA-positive subjects had diabetes family history more common compared to its matched group (67.6% vs. 14.7%, P = 0.000). Postprandial C-peptide in IAA-positive group tended to be lower, but the difference was not statistically significant ( P = 0.084). We concluded that IAA can be used to screen LADA in phenotypic T2DM in the Chinese population. [ABSTRACT FROM AUTHOR]