Lab Values Every NCLEX Candidate Must Know (2026 Edition)

Electrolytes

• Potassium 3.5–5.0 mEq/L — low: muscle weakness, U waves, digoxin toxicity risk; high: peaked T waves, dysrhythmias.
• Sodium 135–145 mEq/L — low: confusion, seizures; high: thirst, restlessness.
• Calcium 9.0–10.5 mg/dL — low: Chvostek and Trousseau signs, tetany; high: weakness, kidney stones.
• Magnesium 1.3–2.1 mEq/L — check during magnesium sulfate therapy; loss of deep tendon reflexes signals toxicity.
• Phosphorus 3.0–4.5 mg/dL — moves opposite to calcium in kidney disease.

Complete blood count

• WBC 5,000–10,000/mm³ — below about 1,000 ANC: neutropenic precautions.
• Hemoglobin about 12–16 g/dL (female) and 14–18 g/dL (male).
• Hematocrit about 37–47% (female) and 42–52% (male).
• Platelets 150,000–400,000/mm³ — below 50,000: bleeding precautions; below 20,000: spontaneous bleeding risk.

Kidney function

• BUN about 6–20 mg/dL.
• Creatinine about 0.6–1.2 mg/dL — the more specific kidney marker.
• Hold or question metformin before contrast dye when kidney function is reduced, per protocol.

Arterial blood gases

Use ROME: Respiratory Opposite, Metabolic Equal.

• pH 7.35–7.45.
• PaCO₂ 35–45 mmHg — the respiratory part.
• HCO₃⁻ 22–26 mEq/L — the metabolic part.
• PaO₂ 80–100 mmHg; SpO₂ 95–100% for most adults.

Coagulation

• PT 11–12.5 seconds; INR 0.8–1.1 — target about 2–3 on warfarin for most indications. Antidote: vitamin K.
• aPTT 30–40 seconds — therapeutic on heparin about 1.5–2.5 × control. Antidote: protamine sulfate.

Glucose and endocrine

• Fasting glucose about 70–100 mg/dL; below 70: treat hypoglycemia with 15 g fast-acting carbohydrate and recheck in 15 minutes.
• HbA1c below 5.7% normal; 6.5% or higher is in the diabetes range.

Cardiac and others

• Troponin — elevated in myocardial injury; trend over time.
• BNP below 100 pg/mL — rises in heart failure.
• Digoxin therapeutic about 0.5–2.0 ng/mL; toxicity signs: nausea, vision changes, bradycardia.
• Lithium therapeutic about 0.6–1.2 mEq/L; above 1.5 shows toxicity risk.

How to study lab values without memorizing a phone book

Learn each value as a story: normal range, what makes it go up or down, the symptom you would see, and the first nursing action. Study ten values a day with flashcards, then answer practice questions that use them in context. Naxlex lab value questions always come with rationales that tie the number to the priority action.

Practice questions with rationales

Original NCLEX-style questions. Choose an answer to see the rationale.

Frequently asked questions