Definition, Diagnostic Criteria, Screening, Diagnosis, and Classification of Diabetes and Categories of Glucose Intolerance

Abstract

The diagnostic criteria for diabetes mellitus (DM) have undergone a sea change over the last several decades. The specific cutoff points for diagnosing DM still remain a matter of intense debate. Prediabetes is an intermediate state of hyperglycemia characterized by elevated plasma glucose levels above normal, though not qualifying for the diagnosis of DM. Recently, the glycosylated hemoglobin has been included as an additional parameter for the diagnosis of DM. The American Diabetes Association (ADA) 2017 guidelines have laid down certain risk factors for screening for diabetes and prediabetes. DM can be classified based on the underlying pathogenic mechanisms into the following categories: type 1 DM, type 2 DM, gestational diabetes mellitus (GDM), and secondary DM. Type 1 DM is characterized by complete cellular-mediated destruction of the β-cells resulting in insulinopenia and insulin replacement therapy for survival. In contrast to type 1 diabetes, type 2 DM is characterized by relative insulin deficiency due to β-cell dysfunction and resistance to the action of insulin in target tissues. GDM is defined as any degree of hyperglycemia that is first detected during pregnancy and encompasses true GDM and pre-existing DM. There is no one universal criteria for diagnosing GDM. Secondary diabetes group includes monogenic forms of diabetes and others with an underlying genetic defect affecting insulin secretion and action, diseases affecting the pancreas, diabetes associated with endocrine disorders, drug-induced diabetes, and post-transplantation diabetes.