What's something from the patient's history and/or investigations used to accurately distinguish between type 1 and 2 diabetes?

GAD antibodies: Type 1 diabetes has anti-islet antibodies or anti-gad antibodies; these can be measured if the precise diagnosis is important. Type 1 diabetics are "younger", require Insulin from the beginning, are thinner, and are prone to ketoacidosis. Type 2's usually don't require Insulin initially, are heavier, older, and often have a stronger family history. There are some people who are hard to classify.