What are the recommended steps for diagnosing and managing type 1 and type 2 diabetes in adults, including lifestyle interventions, medication selection, target glycated hemoglobin, monitoring, and special considerations such as cardiovascular disease, chronic kidney disease, heart failure, pregnancy, and elderly patients?

Diabetes Management Guidelines

Diagnosis

Diagnose type 2 diabetes when fasting plasma glucose ≥126 mg/dL, HbA1c ≥6.5%, or 2-hour glucose during 75-g oral glucose tolerance test ≥200 mg/dL. 1, 2

• Confirm diagnosis with repeat testing on a subsequent day, except when random plasma glucose ≥200 mg/dL with classic hyperglycemic symptoms 2
• Screen adults 40-70 years who are overweight or obese every 3 years 2
• Screen annually starting at age 45, or earlier if major risk factors present (obesity, family history, hypertension, gestational diabetes, Hispanic/American Indian/Alaska Native/Asian/Black ethnicity) 1, 2

Glycemic Targets

Target HbA1c between 7-8% for most adults with type 2 diabetes. 3, 4, 5

• Deintensify treatment immediately when HbA1c falls below 6.5% by reducing medication doses or discontinuing agents to prevent hypoglycemia 3, 4, 5
• Tighter targets (6.0-7.0%) may be appropriate for patients with life expectancy >10-15 years, minimal microvascular disease, and when safely achievable 4
• Looser targets (8.0-8.5%) are appropriate for patients with life expectancy <10 years, advanced age (≥80 years), multiple comorbidities (≥3 chronic conditions), dementia, end-stage organ disease, or nursing home residence 3
• Do not target HbA1c above 8.5% as this exposes patients to hyperglycemic complications including dehydration, hyperosmolar syndrome, and poor wound healing 3

First-Line Pharmacologic Therapy

Start metformin immediately at diagnosis combined with lifestyle modifications unless contraindicated. 3, 4, 5, 6, 1

• Metformin reduces cardiovascular events and mortality, is inexpensive, and causes minimal hypoglycemia 3, 4
• Monitor vitamin B12 levels during long-term use, especially if anemia or peripheral neuropathy develops 5, 6
• Metformin can be used safely with eGFR ≥30 mL/min/1.73 m² 3

Lifestyle Interventions

Prescribe 150 minutes per week of moderate-intensity aerobic exercise plus 2-3 sessions weekly of resistance training on nonconsecutive days. 3, 4, 6

• Restrict calorie intake to 1500 kcal/day 4, 6
• Limit dietary fat to 30-35% of total energy 4, 6
• Physical activity reduces HbA1c by 0.4-1.0% and improves cardiovascular risk factors 1
• Weight loss of 5-7% improves mobility, physical functioning, and cardiometabolic risk factors in older adults 3

Second-Line Therapy: Organ-Protection Algorithm

When metformin plus lifestyle modifications fail to achieve HbA1c target after 3 months, select second-line agent based on comorbidities rather than glycemia alone. 3, 4, 5

SGLT2 Inhibitors Preferred When:

• Patient has heart failure (any ejection fraction) - reduces heart failure hospitalizations by 18-25% 3, 4, 1
• Patient has chronic kidney disease with eGFR 20-60 mL/min/1.73 m² and/or albuminuria - slows CKD progression by 24-39% and reduces cardiovascular events 3, 4, 1
• Goal is cardiovascular mortality reduction 3, 4
• Note: Glycemic efficacy diminishes when eGFR <45 mL/min/1.73 m²; use primarily for organ protection below this threshold 3, 4

GLP-1 Receptor Agonists Preferred When:

• Patient has elevated stroke risk - reduces stroke incidence by 12-26% 3, 4
• Substantial weight loss is therapeutic priority - high-potency agents produce >5% weight loss in most patients 3, 4, 1
• Advanced CKD with eGFR <30 mL/min/1.73 m² when SGLT2 inhibitors unsuitable 3, 4
• Goal is all-cause mortality reduction 3, 4
• For patients with BMI >25, tirzepatide is favored - achieves mean weight loss of 8.5 kg with approximately 67% achieving ≥10% weight loss 4, 6

Avoid DPP-4 Inhibitors

Do not add DPP-4 inhibitors as second-line therapy because they lack mortality and morbidity benefits compared to SGLT2 inhibitors or GLP-1 receptor agonists. 4, 5

Medication Reassessment

Re-evaluate medication regimen every 3-6 months and adjust based on glycemic control, weight goals, metabolic comorbidities, and hypoglycemia risk. 3, 4, 5, 6

• Avoid therapeutic inertia - modify treatment promptly when patients fail to meet individualized goals 5, 6

Deintensification and Simplification

When SGLT2 inhibitors or GLP-1 receptor agonists achieve adequate glycemic control, discontinue or reduce sulfonylureas and long-acting insulins to prevent severe hypoglycemia. 4, 5, 6

• Sulfonylureas and intensive insulin regimens increase hypoglycemia risk without mortality benefit 4, 5
• In older adults, simplify complex insulin regimens to match self-management abilities - reduces hypoglycemia and distress without worsening glycemic control 3
• Overtreatment is common in older adults and must be avoided 3

Insulin Therapy

Approximately one-third of adults with type 2 diabetes require insulin during their lifetime. 4, 1

• When insulin is required, combine with GLP-1 receptor agonist rather than using insulin alone 5
• In cost-constrained situations: maximize glipizide dose first; if HbA1c remains >8%, add basal insulin and immediately reduce glipizide dose by 50% to prevent severe hypoglycemia 4, 6

Special Populations

Older Adults (≥65 years)

In older adults at increased risk of hypoglycemia, prefer medication classes with low hypoglycemia risk (metformin, SGLT2 inhibitors, GLP-1 receptor agonists, DPP-4 inhibitors). 3

• Target HbA1c 7.5-8.0% for those with limited life expectancy (<10 years) or extensive comorbidities 3
• For patients with life expectancy <10 years due to advanced age (≥80 years), nursing home residence, or chronic conditions (dementia, cancer, end-stage kidney disease, severe COPD/CHF), treat to minimize hyperglycemic symptoms rather than targeting specific HbA1c 3
• Ensure optimal nutrition with adequate protein intake to prevent sarcopenia and frailty 3
• Consider costs of care and insurance coverage when developing treatment plans to reduce cost-related nonadherence 3
• Use continuous glucose monitoring in older adults with type 1 diabetes to reduce hypoglycemia risk 3
• Consider automated insulin delivery systems in older adults with type 1 diabetes based on individual ability 3

Cardiovascular Disease

For patients with established atherosclerotic cardiovascular disease, target LDL-cholesterol <70 mg/dL using high-intensity statin therapy. 4

• Prescribe moderate-to-high-intensity statin to all adults ≥40 years with diabetes and additional cardiovascular risk factors 4
• Statin therapy reduces coronary heart disease events by 19-42% 4
• Aggressive blood pressure control to <140/80 mmHg halves cardiovascular event risk 4
• ACE inhibitors or ARBs are preferred first-line antihypertensive agents, especially with albuminuria 4

Chronic Kidney Disease

SGLT2 inhibitors slow CKD progression, lower cardiovascular events, and reduce heart failure hospitalizations in patients with eGFR 20-60 mL/min/1.73 m² and/or albuminuria. 4

• ACE inhibitors and ARBs diminish development and progression of albuminuria 4
• GLP-1 receptor agonists are preferred when eGFR <30 mL/min/1.73 m² 3, 4

Pregnancy

• Refer to specialized guidelines for preconception, pregnancy, and postpartum management 3

Aspirin for Cardiovascular Prevention

Prescribe primary-prevention aspirin 75-162 mg/day only when 10-year cardiovascular risk exceeds 10% (men >50 years or women >60 years with ≥1 additional major risk factor). 4

• Avoid aspirin for primary prevention when 10-year risk <5% because bleeding risk outweighs benefit 4
• For secondary prevention, prescribe aspirin 75-162 mg/day in all patients with diabetes and history of cardiovascular disease 4
• Use clopidogrel 75 mg/day in patients with documented aspirin allergy 4

Microvascular Complications

Tight glycemic control reduces incidence of retinopathy and diabetic peripheral neuropathy, though benefits require long-term follow-up (10-17 years) to manifest. 4

• Intensive glycemic control shows modest reductions in clinical microvascular events (absolute reduction 3.5%) after extended follow-up 1
• Screen for cognitive impairment and dementia routinely in older adults, as cognitive decline increases hypoglycemia risk 3

Critical Pitfalls to Avoid

• Never delay treatment intensification when patients fail to meet glycemic targets - therapeutic inertia worsens long-term outcomes 5, 6
• Never continue sulfonylureas once SGLT2 inhibitors or GLP-1 agonists achieve glycemic control - they increase hypoglycemia without mortality benefit 4, 5, 6
• Never target HbA1c below 6.5% - this mandates immediate deintensification 3, 4, 5
• Never use DPP-4 inhibitors as second-line therapy - they lack mortality benefit 4, 5
• Never ignore cost barriers - discuss medication costs and prescribe generics when available 3, 5
• Never overlook social determinants of health - assess social risk factors and connect patients to community services 5