The present invention provides a method of diagnosing type 1 diabetes (T1D) or latent autoimmune diabetes in adults (LADA) in a subject comprising testing a sample from the subject for the presence or absence of antibodies against modified insulin, wherein the presence of antibodies against modified insulin in the sample is indicative of T1D or LADA in the subject. The invention also provides a method of treating T1D or LADA in a subject in need thereof. Also provided are methods of determining the 10 therapeutic effectiveness of a therapeutic agent in treating T1D or LADA in a subject diagnosed with T1D or LADA. A kit for diagnosing T1D or LADA in a subject comprising reagents for determining the presence of antibodies against modified insulin in a sample from a subject is also provided.
