Guide — Endocrine
Diabetes Mellitus Fundamentals
A comprehensive foundation for understanding diabetes mellitus — Type 1, Type 2, prediabetes, risk factors, clinical manifestations, diagnostic criteria, long-term complications, and nursing considerations.
12 min read · Endocrine
Educational use only. This content is designed to support nursing education and NCLEX preparation. Clinical decisions must always follow institutional protocols and current clinical guidelines. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
Overview
Diabetes mellitus is a chronic metabolic disorder characterized by hyperglycemia resulting from defects in insulin secretion, insulin action, or both. It is the most common endocrine disorder in clinical nursing practice and a top-priority NCLEX topic.
The pancreatic beta cells normally secrete insulin in response to rising blood glucose. Insulin allows glucose to enter cells for energy. In diabetes, this process fails — either because the immune system destroys the beta cells (Type 1) or because the body becomes resistant to insulin and beta cell function progressively declines (Type 2).
The result in both cases: glucose accumulates in the blood (hyperglycemia) while cells are starved of fuel, triggering a cascade of short- and long-term consequences.
Type 1 vs Type 2 Diabetes
| Feature | Type 1 | Type 2 |
|---|---|---|
| Mechanism | Autoimmune destruction of beta cells — absolute insulin deficiency | Insulin resistance + progressive beta cell dysfunction — relative insulin deficiency |
| Onset age | Typically childhood/young adult; any age possible | Typically adult; increasingly seen in youth |
| Body habitus | Usually thin or normal weight | Usually overweight or obese |
| Insulin requirement | Always — cannot survive without insulin | Variable — diet/pills first; insulin added as disease progresses |
| Ketoacidosis risk | HIGH — no endogenous insulin to suppress ketogenesis | Low — unless severe illness or late-stage disease |
| Onset presentation | Acute — days to weeks; often presents in DKA | Insidious — often asymptomatic; detected on routine labs |
| Autoantibodies | Present (islet cell, anti-GAD, insulin antibodies) | Absent |
| C-peptide | Low or undetectable — no beta cell function | Normal or elevated early; decreases over time |
| Genetic link | HLA-DR3, HLA-DR4 associations | Polygenic — strong lifestyle and family history component |
Prediabetes
Prediabetes is a state of impaired glucose regulation that precedes Type 2 diabetes. Blood glucose is above normal but below the diabetic threshold.
| Test | Normal | Prediabetes | Diabetes |
|---|---|---|---|
| Fasting glucose | <100 mg/dL | 100–125 mg/dL | ≥126 mg/dL |
| 2-hour OGTT | <140 mg/dL | 140–199 mg/dL | ≥200 mg/dL |
| A1C | <5.7% | 5.7–6.4% | ≥6.5% |
Prediabetes is reversible with lifestyle intervention — 5–7% weight loss and 150 min/week moderate exercise reduces progression risk by ~58% (DPP trial). Metformin may also be used in high-risk individuals.
Risk Factors
Type 1 Risk Factors
- ✦Family history (first-degree relative)
- ✦HLA-DR3 or HLA-DR4 genotype
- ✦Geographic: higher incidence in Northern Europe
- ✦Possible viral triggers (enterovirus)
- ✦Other autoimmune conditions (Hashimoto's, celiac)
Type 2 Risk Factors
- ✦Overweight or obese (BMI ≥25)
- ✦Physical inactivity
- ✦First-degree relative with Type 2 DM
- ✦Age ≥45 years
- ✦Prediabetes (A1C 5.7–6.4%)
- ✦Gestational diabetes history
- ✦Polycystic ovary syndrome (PCOS)
- ✦Hypertension or dyslipidemia
- ✦Race/ethnicity: Black, Hispanic, Asian, Native American
Clinical Manifestations — The 3 Ps
| Symptom | Mechanism | Clinical Note |
|---|---|---|
| Polyuria (excessive urination) | Osmotic diuresis — glucose acts as an osmotic agent in renal tubules, pulling water into urine | Leads to dehydration, electrolyte loss, nocturia |
| Polydipsia (excessive thirst) | Dehydration from polyuria triggers thirst center in hypothalamus | Compensatory response — patients may drink several liters per day |
| Polyphagia (excessive hunger) | Cells cannot use glucose for energy despite abundant blood glucose — cellular starvation signals hunger | More prominent in Type 1; weight loss despite increased eating |
| Weight loss | Glucose lost in urine; fat and muscle catabolized for energy (especially Type 1) | Dramatic weight loss in new-onset Type 1 DKA; may be subtle in Type 2 |
| Fatigue | Cells unable to use glucose → energy deficit | Often the presenting complaint in Type 2 DM |
| Blurred vision | High glucose causes osmotic lens swelling, altering focal length | Usually reversible with glucose control — not the same as diabetic retinopathy |
| Recurrent infections | Hyperglycemia impairs neutrophil and immune function | Fungal (Candida), UTIs, skin infections — common early sign in undiagnosed Type 2 |
Diagnostic Criteria
Diagnosis requires one of the following (confirmed by repeat testing on a separate day if asymptomatic):
- 1.Fasting plasma glucose ≥126 mg/dL (8+ hours fasting)
- 2.2-hour plasma glucose ≥200 mg/dL during 75g oral glucose tolerance test (OGTT)
- 3.A1C ≥6.5% (certified laboratory method)
- 4.Random plasma glucose ≥200 mg/dL WITH classic hyperglycemia symptoms (3 Ps) — no confirmation needed
Long-Term Complications
| Complication | Mechanism | Clinical Significance |
|---|---|---|
| Diabetic retinopathy | Microvascular — basement membrane thickening of retinal capillaries; neovascularization | Leading cause of new blindness in adults ages 20–74; annual dilated eye exam required |
| Diabetic nephropathy | Microvascular — glomerular hyperfiltration, microalbuminuria progressing to proteinuria | Leading cause of end-stage renal disease (ESRD); monitor creatinine, GFR, urine albumin |
| Diabetic neuropathy | Microvascular — nerve ischemia; accumulation of sorbitol in Schwann cells | Most common: peripheral (stocking-glove distribution); autonomic (gastroparesis, orthostatic hypotension, neurogenic bladder) |
| Diabetic foot ulcers | Peripheral neuropathy (loss of protective sensation) + peripheral vascular disease + infection | Leading cause of non-traumatic lower extremity amputation; daily foot inspection essential |
| Cardiovascular disease | Macrovascular — accelerated atherosclerosis | 2–4× higher risk of CAD, stroke, MI; leading cause of death in Type 2 DM |
| Peripheral arterial disease (PAD) | Macrovascular — lower extremity arterial occlusion | Claudication, poor wound healing, gangrene; ABI assessment for screening |
Nursing Considerations
Blood glucose monitoring
Establish baseline and post-meal patterns. Know when to check (fasting, pre-meal, 2-hour post-prandial, bedtime). Critical values: <70 mg/dL (hypoglycemia) and >400 mg/dL (critical hyperglycemia).
Medication safety
Insulin is a HIGH-ALERT medication. Verify dose with second nurse per policy. Know which insulins can be mixed (regular + NPH) and which cannot (glargine, detemir — must not be mixed).
Hypoglycemia recognition
Symptoms at <70 mg/dL: shakiness, diaphoresis, tachycardia, hunger, confusion. Treat with 15g fast-acting carbohydrate (Rule of 15). Severe hypoglycemia: IV dextrose or glucagon.
Sick day management
Never omit insulin when sick — illness increases counter-regulatory hormones and glucose. Monitor glucose more frequently. Check ketones in Type 1 DM if glucose >250. Stay hydrated.
Foot care
Inspect feet daily. Never walk barefoot. Report any wound, blister, or color change. Ensure podiatry referral for foot problems. Nail trimming — straight across, not too short.
A1C monitoring
Reflects average glucose over ~3 months. Goal <7% for most adults (individualized). Each 1% A1C reduction = significant complication risk reduction.
NCLEX Pearls
- ✦Type 1 DM = autoimmune destruction of beta cells = absolute insulin deficiency = always requires insulin.
- ✦Type 2 DM = insulin resistance + progressive beta cell failure = relative deficiency = may be managed without insulin initially.
- ✦3 Ps = Polyuria + Polydipsia + Polyphagia — the classic triad of hyperglycemia.
- ✦Diagnosis: FPG ≥126 (fasting), A1C ≥6.5%, Random ≥200 with symptoms, 2-hr OGTT ≥200.
- ✦Microvascular complications: retinopathy, nephropathy, neuropathy (small vessel disease).
- ✦Macrovascular complications: CAD, stroke, PAD (large vessel atherosclerosis).
- ✦Hypoglycemia (<70 mg/dL): diaphoresis, shakiness, tachycardia, confusion — treat with 15g carbs.
- ✦Insulin is a HIGH-ALERT medication — always double-check with a second nurse.
- ✦Never omit insulin during illness — illness raises blood glucose through counter-regulatory hormones.
Related Resources
Standards & sources
Fact-checked Jun 20, 2026This page is written to align with American Diabetes Association (ADA) Standards of Care · American Association of Clinical Endocrinology (AACE). It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →