Diabetes Mellitus

Diabetes Mellitus as a Core FNP Competency

Diabetes mellitus (DM) is a group of metabolic disorders characterized by chronic hyperglycemia resulting from defects in insulin secretion, insulin action, or both. For the Family Nurse Practitioner (FNP), managing diabetes in adult and geriatric populations is a core competency, as the prevalence increases with age. This topic is high-yield for certification exams and clinical practice due to the complexity of pharmacotherapy, comorbidity management, and prevention of complications.^[1]

Types, Diagnostic Markers, and Acute States

• Type 1 Diabetes (T1DM): Autoimmune destruction of pancreatic beta cells → absolute insulin deficiency. Onset often in childhood or young adulthood, but can occur at any age.
• Type 2 Diabetes (T2DM): Progressive insulin resistance with relative insulin deficiency. Strongly associated with obesity, physical inactivity, and aging.
• Prediabetes: Impaired fasting glucose (IFG) 100–125 mg/dL or impaired glucose tolerance (IGT) 140–199 mg/dL on 2-hour OGTT. High risk for progression to T2DM.^[2]
• Gestational Diabetes Mellitus (GDM): Glucose intolerance first recognized during pregnancy. Screen at 24–28 weeks.
• Hemoglobin A1c (HbA1c): Reflects average blood glucose over 2–3 months. Diagnostic threshold: ≥ 6.5% (ADA).^[1]
• Diabetic Ketoacidosis (DKA): Life-threatening complication more common in T1DM, characterized by hyperglycemia, ketonemia, and metabolic acidosis.
• Hyperosmolar Hyperglycemic State (HHS): Severe hyperglycemia (>600 mg/dL) without significant ketosis, seen often in T2DM, especially older adults.

Pathophysiologic Mechanisms in Type 2 Diabetes

Insulin Resistance and Beta-Cell Dysfunction in T2DM

1. Insulin resistance: Tissues (muscle, fat, liver) fail to respond normally to insulin → decreased glucose uptake. Compensatory hyperinsulinemia occurs initially.
2. Beta-cell dysfunction: Over time, pancreatic beta cells cannot maintain high insulin output → relative insulin deficiency. This is progressive.
3. Increased hepatic glucose production: Liver releases glucose despite hyperglycemia, worsening fasting glucose.
4. Incretin defect: Reduced GLP-1 activity impairs postprandial insulin secretion.^[3]

In older adults, age-related changes (sarcopenia, reduced renal function, polypharmacy) complicate management. Atypical presentations (e.g., fatigue, confusion, incontinence) are common.^[4]

Classic and Age‑Atypical Presentations

• Classic triad: Polyuria, polydipsia, polyphagia (often with weight loss in T1DM).
• Blurred vision: Due to osmotic lens changes from hyperglycemia.
• Fatigue, recurrent infections (e.g., yeast, urinary tract), slow wound healing.
• Neuropathic symptoms: Numbness, tingling, burning pain in distal extremities (diabetic peripheral neuropathy).
• In older adults: Nonspecific complaints (falls, confusion, incontinence, dizziness) may signal hyperglycemia or hypoglycemia.^[4]

ADA Diagnostic Criteria and Screening Protocols

Diagnostic Criteria (ADA)^[1]

• Fasting plasma glucose (FPG) ≥ 126 mg/dL (fasting = no caloric intake for ≥ 8 hours).
• 2-hour plasma glucose ≥ 200 mg/dL during 75g OGTT.
• HbA1c ≥ 6.5% (lab certified, standardized).
• Symptomatic patient with random glucose ≥ 200 mg/dL.

Repeat testing to confirm unless unequivocal hyperglycemia with metabolic decompensation.

Recommended Screening and Monitoring

• Screen all adults ≥ 45 years or younger if overweight and risk factors (family history, hypertension, dyslipidemia, PCOS). Use FPG, HbA1c, or 2h OGTT.
• Self-monitoring of blood glucose (SMBG): Frequency individualized. For patients on insulin, multiple daily checks are essential.
• Continuous glucose monitoring (CGM): Increasingly used, reduces need for fingersticks, provides glucose trends.
• Kidney function: Annual eGFR, urine albumin-to-creatinine ratio (UACR) for nephropathy screening.
• Lipid panel, blood pressure, foot exam at least annually.

Glycemic Goals and Therapeutic Modalities

Glycemic Goals (ADA)^[1]

• General adults: HbA1c < 7.0%. Preprandial glucose 80–130 mg/dL, peak postprandial <180 mg/dL.
• Older adults (≥65): Less stringent goals if life expectancy limited, high comorbidity burden, or hypoglycemia risk. HbA1c < 7.5–8.0% for moderate health, < 8.5% for poor health.^[4]
• Avoid overtreatment: In older patients, hypoglycemia is particularly dangerous (falls, arrhythmias, cognitive decline).

Lifestyle Management

• Medical nutrition therapy: Emphasize vegetables, whole grains, lean protein, healthy fats. Limit refined carbs and added sugars. Carbohydrate counting for insulin users.
• Physical activity: At least 150 minutes/week of moderate-intensity aerobic activity, plus resistance training 2x/week. Contraindications if active foot ulcers, unstable cardiac disease.
• Weight loss: 5–10% reduction in body weight improves glycemic control and comorbidities.^[2]

Pharmacologic Therapy (T2DM)

Stepwise approach based on patient characteristics.

• First-line: Metformin – reduces hepatic glucose output, improves insulin sensitivity, weight neutral, low hypoglycemia risk. Contraindicated if eGFR <30 mL/min. Short-term hold before iodinated contrast.^[1]
• Combination therapy: If HbA1c above target after 3 months on metformin, add second agent.
• Common second agents:
  • SGLT2 inhibitors (empagliflozin, dapagliflozin): Reduce cardiovascular and renal risk. Monitor for euglycemic DKA, genital infections.
  • GLP-1 receptor agonists (liraglutide, semaglutide): Promote weight loss, reduce major adverse cardiovascular events (MACE). Injectables; some oral semaglutide.
  • DPP-4 inhibitors (sitagliptin, linagliptin): Well tolerated, weight neutral, low risk.
  • Sulfonylureas (glipizide, glimepiride): Effective but risk hypoglycemia and weight gain. Use cautiously in elderly.
  • Thiazolidinediones (pioglitazone): Insulin sensitizer; concerns about fluid retention, fracture risk, bladder cancer.
  • Insulin: Basal (NPH, glargine, detemir, degludec) or prandial (rapid-acting). Indicated when oral agents fail or severe hyperglycemia (HbA1c >10% or symptoms).^[3]

Simplifying Insulin Regimens for Older Adults

• Simpler regimens preferred: basal insulin once daily, adjusted gradually.
• Avoid sliding-scale insulin alone – promotes wide glucose fluctuations.
• Hypoglycemia awareness may be impaired; educate caregivers.

Hypoglycemia, Micro‑/Macrovascular, and Emergency Management

Hypoglycemia

• Glucose <70 mg/dL. Causes: missed meals, excess insulin or sulfonylureas, exercise, alcohol, renal insufficiency.
• Symptoms: Autonomic (tremor, palpitations, sweating) and neuroglycopenic (confusion, slurred speech, seizure, coma). In older adults, autonomic symptoms often blunted → danger.
• Treatment: "Rule of 15" – consume 15g fast-acting carbohydrate, recheck in 15 min; repeat if <70 mg/dL. Use glucagon if unable to swallow.
• Prevention: Individualize glucose goals, adjust medications during illness, educate patient/family.

Chronic Complications

• Microvascular: Retinopathy (annual dilated eye exam), nephropathy (ACEi or ARB for UACR >30 mg/g), neuropathy (pregabalin, duloxetine, gabapentin for pain; foot care).
• Macrovascular: Coronary artery disease, stroke, peripheral artery disease. Manage hypertension and dyslipidemia aggressively. Statin therapy for most patients with diabetes ≥40 years.^[1]
• Diabetic foot ulcers: Screen annually with 10g monofilament test; refer for podiatry if abnormal.

Hyperglycemic Emergencies

• DKA: Urgent – IV fluids, insulin drip, electrolyte repletion, treat underlying cause.
• HHS: More common in elderly; marked dehydration, high mortality. Aggressive fluid resuscitation, careful insulin, monitor for thrombosis.

Critical Test Benchmarks and Clinical Pearls

• Know diagnostic thresholds: FPG ≥126, 2h OGTT ≥200, HbA1c ≥6.5% – memorize.
• Metformin is first-line for T2DM unless contraindicated. Avoid in renal impairment (eGFR <30).
• In older patients, prioritize safety over tight control. Individualized HbA1c goals (7.5–8.5%) are tested often.
• SGLT2 inhibitors and GLP-1 agonists reduce cardiovascular and renal outcomes – key for high-risk patients.
• Hypoglycemia is an emergency – assessment, treatment (15g carbs, recheck), prevention strategies.
• Annual screening: Foot exam (monofilament), dilated eye exam, urine albumin, eGFR, lipid panel.
• Memory aid for atherosclerosis risk in diabetes: "Lipids, BP, and stop smoking – ABCDES of diabetes care."
• Contrast-induced nephropathy: Hold metformin for 48 hours after iodinated contrast, re-evaluate renal function before restarting.

References

1. American Diabetes Association. 9. Pharmacologic Approaches to Glycemic Treatment: Standards of Care in Diabetes—2024. Diabetes Care. 2024;47(Suppl 1):S158–S178. doi:10.2337/dc24-SINT
2. Centers for Disease Control and Prevention. Prediabetes – Your Chance to Prevent Type 2 Diabetes. Updated 2024. Accessed 2025.
3. Davies MJ, Aroda VR, Collins BS, et al. Management of Hyperglycemia in Type 2 Diabetes, 2022. A Consensus Report by the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD). Diabetes Care. 2022;45(11):2753–2786. doi:10.2337/dci22-0034
4. American Diabetes Association. 13. Older Adults: Standards of Care in Diabetes—2024. Diabetes Care. 2024;47(Suppl 1):S244–S257. doi:10.2337/dc24-S013
5. Lewis SL, Bucher L, Heitkemper MM, Harding MM. Medical-Surgical Nursing: Assessment and Management of Clinical Problems. 11th ed. Elsevier; 2022. ISBN 978-0323786098.