Diabetes mellitus refers to several metabolic disorders that share persistently high blood glucose, due to too little insulin, poor response to insulin, or both. Insulin moves glucose into cells, stores glucose as glycogen, and prevents breakdown of fat and protein. Without effective insulin, glucose stays in the blood while cells starve.

Other types: gestational diabetes (diagnosed in pregnancy) and diabetes from other causes (e.g., pancreatic disease, corticosteroids).

Classic symptoms ("3 Ps") — polyuria (osmotic diuresis), polydipsia (dehydration), polyphagia (cells lack glucose), plus weight loss (type 1), fatigue, blurred vision, and slow wound healing.

Subjective

• Thirst, frequent urination, hunger, fatigue, blurred vision
• Numbness, tingling, or burning in the feet (neuropathy)
• Frequent infections (skin, urinary, vaginal yeast)

Objective

• Elevated blood glucose, glycosuria
• Weight changes; acanthosis nigricans (insulin resistance)
• Foot assessment: skin integrity, pulses, sensation (monofilament), deformities
• Signs of complications: retinopathy, elevated blood pressure, edema

Diagnostic criteria. Without unequivocal hyperglycemia, diagnosis requires two abnormal results (from the same sample or two separate samples). A random glucose ≥ 200 mg/dL (11.1 mmol/L) with classic symptoms is diagnostic on its own.

A1C is less reliable with anemia, hemoglobin variants, or thalassemia — use glucose-based tests in these clients.

Monitoring tests

• A1C — reflects average glucose over about 2–3 months; common target for many adults < 7%, individualized
• Self-monitoring of blood glucose (SMBG) or continuous glucose monitoring (CGM)
• Urine albumin-to-creatinine ratio (UACR) — increased albuminuria (≥ 30 mg/g) is the earliest sign of diabetic kidney disease (formerly called "microalbuminuria")
• Serum creatinine / eGFR — before and during metformin therapy
• Dilated eye exam — type 2: at diagnosis; type 1: within 5 years of diagnosis; then every 1–2 years
• Comprehensive foot exam at least yearly; lipid profile

Lifestyle (all clients)

• Individualized medical nutrition therapy; consistent carbohydrate intake, fiber-rich foods, limited added sugars and saturated fat
• Physical activity: about 150 minutes/week of moderate aerobic activity plus resistance training, as tolerated
• Weight management; smoking cessation

Non-insulin medications (type 2)

Insulin

Onset values are approximate; check the specific product. Some rapid-acting analogs are also labeled for supervised IV use, but regular insulin is the standard IV insulin. Detemir has been discontinued in some markets, including the US.

Listed in priority order.

1. Recognize and treat hypoglycemia
   • Level 1: < 70 mg/dL (3.9 mmol/L) · Level 2: < 54 mg/dL (3.0 mmol/L) · Level 3: severe event with altered mental or physical status requiring assistance
   • Signs: shakiness, sweating, tachycardia, anxiety, hunger, confusion, seizures, loss of consciousness. Beta blockers can mask adrenergic signs; some clients have hypoglycemia unawareness
   • Conscious and able to swallow → "Rule of 15": give 15 g of fast-acting carbohydrate (e.g., 4 oz / 120 mL juice or regular soda, glucose tablets), recheck in 15 minutes, repeat if still < 70 mg/dL (3.9 mmol/L), then give a snack or meal. Avoid high-fat foods (e.g., chocolate) for initial treatment — fat slows absorption
   • Unconscious or unable to swallow → glucagon (IM, SC, or intranasal) or IV dextrose per protocol; never give oral fluids. After glucagon, turn the client on the side (vomiting risk) and give oral carbohydrate once able to swallow
2. Monitor glucose — before meals and at bedtime, or per protocol; in hospital, a common target is 100–180 mg/dL (5.6–10.0 mmol/L)
3. Safe insulin administration
   • Rotate injection sites within the same anatomic area (abdomen absorbs fastest; also thigh, upper arm, buttock) to prevent lipohypertrophy/lipoatrophy
   • Let alcohol dry before injecting; do not massage the site
   • Mixing regular + NPH: draw up clear (regular) before cloudy (NPH)
   • Coordinate rapid-acting insulin with meal delivery
4. Perioperative / NPO care
   • Monitor glucose frequently; oral agents are usually held on the day of surgery
   • SGLT2 inhibitors are stopped 3–4 days before scheduled surgery (per product labeling)
   • Basal insulin is often reduced (e.g., long-acting to about 75–80% of the usual dose) per protocol; prepare for IV insulin infusion with dextrose if glucose is unstable
5. Foot and skin protection — inspect daily, keep dry, treat wounds promptly
6. Assess for complications and coordinate referrals (eye, kidney, podiatry, dietitian, diabetes educator)

• Self-monitoring: technique, recording, and target ranges
• Insulin self-injection: store unopened insulin in the refrigerator and never freeze; in-use vials/pens at room temperature for the labeled period; site rotation; use a new needle for each injection and dispose of it in a puncture-resistant container
• Insulin pump: understand basal vs. bolus; change infusion site regularly and rotate; check glucose often; know what to do if the pump fails or the line is blocked
• Hypoglycemia: recognize symptoms, always carry fast-acting glucose, keep prescribed glucagon and teach family to use it, wear medical identification
• Sick-day rules
  • Continue insulin even if not eating; check glucose every 2–4 hours and ketones if glucose > 240 mg/dL (13.3 mmol/L)
  • If taking an SGLT2 inhibitor, check ketones when ill even if glucose is normal; SGLT2 inhibitors (and usually metformin) are held during vomiting or dehydration as directed by the provider
  • Drink fluids; call the provider for vomiting, persistent high glucose, or moderate/large ketones
• Early-morning highs: check glucose around 2–3 AM to tell the dawn phenomenon (glucose rises toward morning) from the Somogyi effect (nighttime low followed by rebound high)
• Foot care
  • Inspect feet daily, using a mirror for the soles
  • Wash in lukewarm water (test with elbow or thermometer), dry well between toes
  • Cut nails straight across; never go barefoot; wear well-fitting shoes and clean socks
  • Report any cut, blister, or color change promptly
• Nutrition: regular meal timing matched to medication; keep carbohydrates consistent — do not eliminate carbohydrates completely; alcohol can cause delayed hypoglycemia — take it with food
• Exercise: check glucose before activity; if below 100 mg/dL (5.6 mmol/L), eat carbohydrate first; avoid vigorous exercise if glucose > 250 mg/dL (13.9 mmol/L) with ketones; carry a snack

Acute hyperglycemic crises (2024 consensus criteria)

Treatment priorities (DKA/HHS)

1. Fluids first — isotonic saline or balanced crystalloid, about 500–1,000 mL/h for the first 2–4 hours; use smaller volumes and close monitoring with heart failure, kidney failure, or older age
2. Check potassium before insulin — insulin shifts potassium into cells
   • K⁺ < 3.5 mmol/L: replace potassium and delay insulin until K⁺ > 3.5
   • K⁺ below 5.0: add potassium to IV fluids to keep K⁺ about 4–5 mmol/L (confirm urine output)
   • K⁺ above 5.0: no potassium; recheck frequently
3. IV insulin infusion — DKA 0.1 units/kg/h; HHS 0.05 units/kg/h
4. Add dextrose 5–10% when glucose < 250 mg/dL (13.9 mmol/L) to prevent hypoglycemia while ketosis resolves
5. Monitor glucose hourly, electrolytes, mental status, cardiac rhythm. In HHS, lower glucose gradually to reduce the risk of cerebral edema
6. DKA resolution: ketones < 0.6 mmol/L and venous pH ≥ 7.3 or bicarbonate ≥ 18 mmol/L. Give subcutaneous basal insulin 1–2 hours before stopping the IV infusion to prevent rebound DKA

Chronic complications

• Type 1 = absolute insulin deficiency (autoimmune) → insulin required; Type 2 = insulin resistance
• Diagnosis: A1C ≥ 6.5%, FPG ≥ 126 mg/dL (7.0 mmol/L), 2-h OGTT ≥ 200 mg/dL (11.1 mmol/L), random ≥ 200 mg/dL (11.1 mmol/L) with symptoms
• Hypoglycemia < 70 mg/dL (3.9 mmol/L): conscious → 15 g fast carbs, recheck in 15 min; unconscious → glucagon or IV dextrose
• DKA: Kussmaul respirations, fruity breath, dehydration; fluids first, check K⁺ before insulin
• SGLT2 inhibitors can cause DKA with near-normal glucose — check ketones when ill; stop 3–4 days before surgery
• Regular insulin is the standard IV insulin; mix clear before cloudy
• Rotate sites; do not massage after injection
• Metformin: check kidney function (risk of lactic acidosis); hold around iodinated contrast per protocol
• Earliest kidney sign: increased urine albumin (UACR ≥ 30 mg/g)
• Foot care: inspect daily with a mirror, lukewarm water, cut nails straight across
• Sick day: never skip insulin; check glucose and ketones more often