Diabetes mellitus nursing reference: types, management, and complications

Diabetes mellitus affects over 38 million Americans and is the leading cause of end-stage renal disease, adult-onset blindness, and non-traumatic lower-limb amputation in the United States. It is one of the highest-yield topics on NCLEX and one of the most encountered conditions across every clinical specialty. This reference brings together the complete pharmacologic, pathophysiologic, and clinical nursing picture in one place: type comparison tables, ADA diagnostic criteria, insulin onset/peak/duration data, DKA vs HHS differentiation, oral medication classes, foot care staging, Somogyi vs dawn phenomenon, and six NCLEX-style questions with full rationales.

Use this page alongside the DKA nursing reference for ketoacidosis deep-dive content, the nursing lab values cheat sheet for glucose and HbA1c interpretation, the electrolyte imbalances reference for potassium and sodium management in hyperglycemic emergencies, and the ABG interpretation guide for metabolic acidosis analysis in DKA.

Type 1 vs type 2 diabetes: clinical comparison

The distinction between type 1 and type 2 diabetes drives fundamentally different nursing assessments, medication regimens, and patient education approaches. This table consolidates the clinical differentiators that appear most frequently in NCLEX questions and clinical practice.

Diagnostic criteria: ADA 2023 standards

The ADA 2023 Standards of Care defines four criteria for diabetes diagnosis — any one is sufficient when confirmed on a repeat test (unless the patient presents with unequivocal hyperglycemia and classic symptoms, in which case a single test result is sufficient).

HbA1c interpretation caveats: HbA1c reflects glucose attachment to hemoglobin over the red blood cell lifespan (approximately 120 days). Conditions altering RBC survival skew results:

• Falsely low HbA1c: hemolytic anemia, G6PD deficiency, blood loss, recent transfusion, sickle cell disease — RBCs have shorter lifespan, less time for glycation
• Falsely high HbA1c: iron deficiency anemia, splenectomy, vitamin B12 deficiency, renal failure — RBCs survive longer, accumulate more glycation
• Not valid: hemoglobin variants (sickle cell trait, thalassemia) — use FPG or OGTT instead

Confirm diagnosis with repeat testing on a different day unless the patient is symptomatic and has random glucose ≥200 mg/dL. For HbA1c reference values alongside other lab values, see the nursing lab values cheat sheet.

Insulin types: onset, peak, duration, and nursing considerations

Insulin timing is one of the highest-yield NCLEX topics. For every type, know whether it peaks, when hypoglycemia risk is highest, and the administration timing relative to meals.

Critical insulin administration principles

• Draw clear before cloudy: When mixing regular (clear) with NPH (cloudy) in one syringe, draw regular first to prevent NPH from contaminating the regular vial and altering its onset profile.
• Rotate within one anatomic region: Absorption rates differ by site — abdomen is fastest, followed by upper arm, thigh, and buttocks. Rotating between regions causes unpredictable pharmacokinetics. Rotate within the same region, spacing injections ≥1 inch apart to prevent lipohypertrophy.
• Lipohypertrophy: Fatty nodules at over-used injection sites slow absorption significantly — always check injection sites during assessment.
• Storage: Unopened insulin: refrigerate at 36–46°F (2–8°C); in-use pens and vials: room temperature up to 28 days (check individual product labeling); never freeze insulin.

DKA vs HHS: differentiation table

Both conditions are hyperglycemic emergencies but differ significantly in pathophysiology, severity, typical patient profile, and management priorities. This distinction is a perennial NCLEX favorite. For complete DKA pathophysiology and management, see the DKA nursing reference.

For ABG interpretation in the context of metabolic acidosis caused by DKA, review the ABG interpretation guide and cross-reference with the electrolyte imbalances reference for potassium replacement protocols.

Nursing interventions: priority order with rationales

Oral and injectable non-insulin medications

Metformin hold criteria (commonly tested)

Diabetic foot care and neuropathy assessment

Diabetic foot disease results from the convergence of three factors: peripheral sensory neuropathy (loss of protective sensation), peripheral arterial disease (impaired healing), and immune dysfunction (increased infection susceptibility). This combination turns minor injuries into major amputations. The nurse’s role is comprehensive assessment, patient education, and timely referral.

Monofilament testing (Semmes-Weinstein 10-g)

The 10-gram Semmes-Weinstein monofilament is the standard screening tool for loss of protective sensation (LOPS):

1. Apply the monofilament perpendicular to the plantar surface until it bends (delivers ~10 g of force)
2. Test 4 sites per foot: 1st, 3rd, and 5th metatarsal heads + plantar great toe
3. Patient closes eyes and states “yes” when sensation is felt
4. Inability to detect monofilament at any site = loss of protective sensation
5. Confirm with 128-Hz tuning fork at dorsum of great toe for vibration sense

Ankle-brachial index (ABI)

The ABI quantifies peripheral arterial disease by comparing blood pressure at the ankle to the arm:

Wagner grading scale for diabetic foot ulcers

Patient education for foot care:

• Inspect feet daily (use a mirror for plantar surface if unable to see directly)
• Wash feet in lukewarm water and dry between toes — hot water causes burns in neuropathic patients who cannot sense temperature
• Moisturize feet but avoid between toes (moisture promotes fungal growth)
• Trim toenails straight across — curved cutting leads to ingrown nails
• Never walk barefoot (indoors or outdoors)
• Avoid heating pads, hot water bottles, and electric blankets on feet
• Wear well-fitting shoes — break in new shoes gradually over days to weeks; check inside of shoes before putting them on
• Report any break in skin, discoloration, swelling, or wound immediately — do not treat at home

Somogyi effect vs dawn phenomenon

Both cause elevated fasting morning blood glucose but have opposite causes and require opposite interventions. Confusing them leads to incorrect insulin adjustments.

Hypoglycemia: recognition, treatment, and the 15-15 rule

Hypoglycemia is defined as blood glucose below 70 mg/dL. It is more immediately life-threatening than hyperglycemia and must be treated before any other assessment or intervention is pursued.

Symptom progression by severity

• Level 1 (BG 54–69 mg/dL) — adrenergic: Shakiness, tremor, diaphoresis (cold sweat), tachycardia, palpitations, pallor, anxiety, hunger — driven by catecholamine release
• Level 2 (BG <54 mg/dL) — neuroglycopenic: Confusion, difficulty concentrating, irritability, slurred speech, blurred vision, headache, behavioral changes — brain glucose deprivation
• Level 3 (severe) — requiring assistance: Seizures, loss of consciousness, inability to self-treat — medical emergency

The 15-15 rule

1. Confirm blood glucose <70 mg/dL
2. Give 15 grams of fast-acting carbohydrate:
   • 4 oz (120 mL) of fruit juice or regular soda
   • 3–4 glucose tablets
   • 1 tablespoon honey or glucose gel
   • 8 oz (240 mL) low-fat milk
3. Wait 15 minutes — recheck blood glucose
4. If still <70 mg/dL, repeat 15 g carbohydrate and recheck in 15 min
5. Once BG ≥70 mg/dL, eat a small snack with protein and complex carbohydrate to sustain levels

For unconscious or severely altered patients:

• In hospital: D50W 25 mL (12.5 g dextrose) IV — first-line treatment for severe hypoglycemia
• Outside hospital: Glucagon 1 mg IM/SC, or intranasal glucagon (Baqsimi) 3 mg into one nostril — works by stimulating hepatic glycogenolysis
• Never give oral glucose to an unconscious or uncooperative patient — aspiration risk

Glucagon kit education for patients and families: Inject glucagon into outer thigh or buttock; after injection, roll patient onto their side (recovery position); call 911 for all severe hypoglycemia events; patient will likely be nauseated on waking.

Hypoglycemia unawareness: Patients with long-standing diabetes and autonomic neuropathy may lose the adrenergic warning symptoms — they experience neuroglycopenic symptoms (confusion, seizure) without the early shakiness/diaphoresis warning. These patients need more frequent monitoring, CGM consideration, and raised glucose targets. Frequent hypoglycemia episodes also blunt the counter-regulatory response — “hypoglycemia begets hypoglycemia.”

Sick day rules

Illness triggers stress hormone release (cortisol, epinephrine, glucagon) that drives blood glucose up, even when patients are not eating. Never stopping insulin during illness is the most important sick day rule.

During illness:

• Check blood glucose every 4 hours (every 2 hours if glucose is rising rapidly)
• Never stop insulin — not even if the patient is not eating; basal insulin at minimum must continue
• Check urine or blood ketones if BG >250 mg/dL (blood ketone meter preferred)
• Take supplemental rapid-acting insulin per sick-day correction factor as prescribed
• Drink 8 oz of calorie-free fluid hourly to maintain hydration and prevent osmotic dehydration
• If unable to eat, substitute carbohydrate-containing fluids (juice, popsicles, regular broth) in small amounts

Call the provider for:

• BG >300 mg/dL despite correction doses
• Moderate-to-large urine ketones or blood ketones >1.5 mmol/L
• Vomiting that prevents keeping fluids or medications down for >2 hours
• Illness lasting >24 hours without improvement
• Signs of dehydration (extreme thirst, dry mouth, decreased urine output, dizziness)

HbA1c targets by population

NCLEX questions with rationales

Question 1 — DKA vs HHS differentiation

A nurse is caring for a patient with a blood glucose of 920 mg/dL, serum osmolality of 348 mOsm/kg, pH 7.38, and absent urine ketones. The patient is severely obtunded. Which condition does this presentation most likely represent?

A. Diabetic ketoacidosis (DKA) B. Hyperglycemic hyperosmolar state (HHS) C. Euglycemic DKA from SGLT-2 inhibitor use D. Lactic acidosis from metformin toxicity

Correct answer: B

Rationale: HHS is defined by extreme hyperglycemia (>600 mg/dL, here 920), serum hyperosmolality (>320 mOsm/kg, here 348), absent or trace ketones, and preserved acid-base status (pH >7.3, here 7.38). The severely obtunded mental status is characteristic — in HHS, altered consciousness correlates with osmolality. DKA (A) would show ketones and low pH. Euglycemic DKA (C) has near-normal glucose by definition. Lactic acidosis (D) would show low pH and elevated anion gap.

Question 2 — Insulin timing for lispro

The nurse is preparing to administer lispro (Humalog) insulin to a patient. The patient’s meal tray has just been delivered. Which action is correct?

A. Administer the lispro now, immediately before the patient begins eating B. Give the lispro 30 minutes before the meal to allow time for onset C. Hold the lispro until the patient finishes the meal to assess how much was eaten D. Administer the lispro only if blood glucose is above 180 mg/dL

Correct answer: A

Rationale: Rapid-acting insulins (lispro, aspart, glulisine) have an onset of 10–15 minutes and peak at 1–2 hours. They are designed to be given at mealtime or within 15 minutes of eating. Giving 30 minutes before (B) is the instruction for regular (short-acting) insulin, not rapid-acting insulin — confusing the two is a common and potentially dangerous error. Holding until after the meal (C) delays onset and will result in postprandial hyperglycemia. Administering only for glucose above 180 (D) describes a sliding-scale approach and ignores the mealtime bolus principle.

Question 3 — Metformin hold criteria

A patient with type 2 diabetes takes metformin 1,000 mg twice daily. The patient is scheduled for an abdominal CT scan with IV contrast at 2 PM today. The patient’s most recent creatinine is 0.9 mg/dL (eGFR 82 mL/min). Which nursing action is correct?

A. Administer the morning metformin dose as scheduled; no special action needed B. Hold the morning metformin dose; administer contrast; restart metformin immediately after the scan C. Hold metformin at the time of the contrast procedure; restart 48 hours after the procedure once renal function is confirmed stable D. Discontinue metformin permanently because the patient is receiving contrast dye

Correct answer: C

Rationale: IV iodinated contrast dye can cause contrast-induced nephropathy. In the setting of reduced renal perfusion, metformin accumulates and increases the risk of lactic acidosis. Current ADA and ACR guidance recommends holding metformin at the time of the IV contrast procedure and restarting 48 hours afterward, once renal function has been confirmed stable. Option A does not account for the contrast risk. Option B restarts too early — renal function must be reassessed at 48 h. Option D is incorrect — the hold is temporary, not permanent. This patient’s eGFR of 82 is normal, but the contrast risk still applies.

Question 4 — Somogyi effect vs dawn phenomenon

A patient with type 1 diabetes reports waking every morning with a blood glucose of 190–220 mg/dL, despite no evening snacking. The night nurse checks a 3 AM blood glucose and finds it to be 52 mg/dL. Which of the following best explains this finding and what is the appropriate intervention?

A. Dawn phenomenon; the intervention is to increase the evening basal insulin dose B. Somogyi effect; the intervention is to decrease the evening insulin dose or add a bedtime snack C. Dawn phenomenon; the intervention is to decrease the evening basal insulin dose D. Somogyi effect; the intervention is to increase the evening rapid-acting insulin dose

Correct answer: B

Rationale: The 3 AM glucose of 52 mg/dL confirms nocturnal hypoglycemia — this is the hallmark that distinguishes the Somogyi effect from the dawn phenomenon. In Somogyi, the evening insulin dose is too high, causing overnight hypoglycemia, which triggers counter-regulatory hormone release (glucagon, epinephrine, cortisol) and rebound morning hyperglycemia. The correct intervention is to reduce the evening insulin dose or provide a bedtime snack with protein and complex carbohydrate to buffer the overnight period. In dawn phenomenon, the 3 AM glucose would be normal or slightly elevated, and the correct intervention would be increasing (not decreasing) basal insulin coverage. Option D would worsen nocturnal hypoglycemia.

Question 5 — SGLT-2 inhibitor and euglycemic DKA

A patient taking empagliflozin (Jardiance) for type 2 diabetes presents to the emergency department with nausea, vomiting, and abdominal pain. Blood glucose is 198 mg/dL. The nurse notes the patient appears fatigued and has rapid breathing. ABG shows pH 7.21. Urine ketones are large. Which complication is most likely occurring?

A. Hyperosmolar hyperglycemic state — the glucose is near-normal because of early presentation B. Euglycemic diabetic ketoacidosis related to SGLT-2 inhibitor use C. Lactic acidosis from empagliflozin accumulation D. Hyperventilation syndrome — the patient is anxious

Correct answer: B

Rationale: Euglycemic DKA is a well-documented complication of SGLT-2 inhibitor therapy. These medications cause glucosuria, which keeps blood glucose near-normal even in the presence of significant ketoacidosis. This creates a diagnostic trap — the blood glucose is not dramatically elevated (here 198 mg/dL), so standard DKA criteria may not be met on glucose alone. However, the combination of: acidotic pH (7.21), large ketones, nausea and vomiting, Kussmaul-pattern breathing, and SGLT-2 inhibitor use constitutes euglycemic DKA until proven otherwise. Lactic acidosis (C) is associated with metformin, not SGLT-2 inhibitors. This scenario highlights the importance of checking ketones in any SGLT-2 inhibitor patient presenting with nausea, abdominal pain, or malaise — regardless of the blood glucose reading.

Question 6 — Hypoglycemia treatment priority

A nurse enters a patient’s room and finds the patient with diabetes unresponsive. The bedside glucometer reads 38 mg/dL. Which action should the nurse take first?

A. Administer 4 oz of orange juice by mouth B. Call the physician to obtain an insulin order reduction C. Administer D50W 25 mL intravenously per standing hypoglycemia protocol D. Check the blood glucose again on a different finger to confirm the reading

Correct answer: C

Rationale: This patient is unresponsive with a critically low blood glucose of 38 mg/dL. In a hospitalized patient who cannot protect their airway, oral glucose administration (A) is contraindicated — the patient is unconscious and cannot swallow safely; aspiration is a serious risk. IV dextrose (D50W 25 mL) is the first-line treatment for severe hypoglycemia in an unconscious hospitalized patient. Most facilities have standing hypoglycemia protocols that allow nurses to administer D50W without a new physician order. While rechecking the glucose (D) might be considered in a borderline reading, an unresponsive patient with glucose of 38 requires immediate treatment — do not delay treatment to recheck. Calling the physician (B) is an appropriate secondary action but not the first priority when the patient requires immediate glucose administration.

Related references

Build a complete endocrine and acute care nursing library with these companion pages:

• DKA nursing reference — complete diabetic ketoacidosis pathophysiology, assessment, and management
• Nursing lab values cheat sheet — glucose, HbA1c, BMP, and metabolic panel interpretation
• Electrolyte imbalances reference — potassium, sodium, and bicarbonate disorders in DKA and HHS
• ABG interpretation guide — metabolic acidosis analysis and compensation in DKA
• CKD and ESRD nursing guide — diabetic nephropathy, KDIGO staging, dialysis
• Hypertension nursing — cardiovascular risk management in diabetes
• Stroke nursing reference — cerebrovascular disease in diabetes
• Sepsis nursing reference — infection as the most common trigger for DKA and HHS
• Drug classifications nursing guide — broader antidiabetic and cardiovascular medication reference

Clinical references: ADA Standards of Care in Diabetes — 2023 (Diabetes Care 2023;46 Suppl 1), StatPearls Type 2 Diabetes Mellitus (NCBI NBK568737), StatPearls Hyperosmolar Hyperglycemic Syndrome (NCBI NBK482142), StatPearls Diabetic Ketoacidosis (NCBI NBK1900), ADA/EASD Consensus Statement on T2D Management 2022, Wagner grading system (Wagner FW Jr, 1981), Semmes-Weinstein monofilament standard protocol (ADA 2023), ADA/ACR Contrast Media Guidelines (metformin hold), ADAG Study (Nathan et al., Diabetes Care 2008).