Diagnosing diabetes mellitus

Diagnosing diabetes mellitus by well-defined, objectively established, laboratory criteria is a relatively recent occurrence. Diabetes was not defined by any laboratory criteria until urine glucose could be measured last century. The use of blood tests for glucose did not develop until well into this century. The discovery of insulin, the wider use of the hypodermic syringe for venesection and the development of micro methods for laboratory analysis permitted the development of blood tests in diagnosing diabetes. The use of insulin to keep young diabetic subjects alive, albeit with elevated glucose levels, lead to the discovery of the association of retinopathy and elevated plasma glucose. This lead to efforts to diagnose diabetes in as mild a form as possible using the oral glucose tolerance test, to prevent such complications occurring. Determining what glucose levels were normal or abnormal then became an issue. Studies of the Pima Indians of Arizona eventually lead to objective definitions of diabetes that have been further refined in the past few years. We also now understand how retinopathy and other diabetes complications may develop. It is the glucose itself 'sticking' to proteins (advanced glycosylation end products) that does the damage. The future holds the promise that genetic diagnoses for diabetes and its complications may lead to the total prevention of diabetes and its effects.