Diabetes Mellitus: Diagnostic Criteria and Management

Classification and Diagnosis

The American Diabetes Association recognizes four main categories of diabetes, including Type 1, Type 2, Gestational Diabetes Mellitus, and Specific Types Due to Other Causes 2
Type 1 Diabetes results from autoimmune destruction of pancreatic β-cells leading to absolute insulin deficiency, and is characterized by the presence of islet cell autoantibodies, anti-insulin antibodies, anti-GAD65 antibodies, and anti-IA-2/IA-2β antibodies in 85-90% of patients at diagnosis 3, 4
The American Diabetes Association establishes that diabetes may be diagnosed using plasma glucose criteria (fasting or 2-hour OGTT) or HbA1c criteria, with specific thresholds for diagnosis, including Fasting Plasma Glucose (FPG) ≥126 mg/dL, 2-hour plasma glucose ≥200 mg/dL, and HbA1c ≥6.5% 2, 1

Chronic hyperglycemia triggers a cascade of damaging biochemical pathways involving oxidative stress, inflammation, and microvascular dysfunction, leading to complications such as retinopathy, nephropathy, and neuropathy 6
Small unmyelinated C fibers and thinly myelinated Aδ fibers are damaged earliest in diabetic neuropathy, before large fiber involvement, and conventional nerve conduction studies may be normal in early diabetic neuropathy 6
Improved glycemic control can slow progression but does not reverse established neuronal loss in diabetic neuropathy 6

Insulin replacement therapy is mandatory for survival in Type 1 Diabetes, and treatment follows a stepwise approach beginning with lifestyle modifications in Type 2 Diabetes 1
The American College of Physicians warns against several diagnostic and management errors, including misdiagnosis of diabetes type at presentation, missing early stages of type 2 diabetes, and focusing only on fasting glucose while ignoring postprandial hyperglycemia 1
Medical nutrition therapy, exercise, and certain pharmacological agents can prevent or delay development of diabetes in patients with prediabetes, and interventions are most effective in individuals with impaired glucose tolerance 5, 2

Improving glycemic control is the primary intervention for preventing and managing complications, and good glycemic control decreases the incidence of diabetic neuropathy, though does not eliminate risk entirely 7, 6
Regular blood glucose monitoring and HbA1c testing are necessary to evaluate long-term glycemic control, and screening for complications including retinopathy, nephropathy, and neuropathy is essential 1, 2, 3