NCLEX Lab Values to Memorize (and How Questions Use Them)
Nurseclex Editorial Team · Updated · 7 min read · Written around the NCSBN test plan
Short answer
Focus on the values that drive decisions: potassium 3.5–5.0, sodium 135–145, glucose 70–110 fasting, BUN 10–20, creatinine 0.6–1.2, and the CBC. NCLEX questions rarely ask for a number alone — they show an abnormal value and ask what you do next.
Key takeaways
- Potassium is the most tested electrolyte because of dysrhythmia risk.
- Learn each value paired with the action it triggers, not in isolation.
- Digoxin, diuretics and insulin questions almost always involve a lab value.
- Your program's reference ranges always win over any chart.
Electrolytes that change your answer
Potassium 3.5–5.0 mEq/L is the classic. Low potassium with digoxin or furosemide raises dysrhythmia risk; high potassium can be life-threatening and is never 'document and move on'.
Sodium 135–145 mEq/L matters most in neuro questions: confusion, seizures and level-of-consciousness changes point you toward sodium or glucose.
- Potassium 3.5–5.0
- Sodium 135–145
- Calcium 9–10.5
- Magnesium 1.3–2.1
Renal and glucose values
BUN 10–20 mg/dL and creatinine 0.6–1.2 mg/dL tell you how the kidneys are doing. Rising creatinine means falling kidney function — hold nephrotoxic drugs and metformin before contrast dye.
Fasting glucose 70–110 mg/dL. In an altered client, check glucose early: hypoglycemia is treatable in minutes and mimics stroke and intoxication.
CBC basics
Hemoglobin roughly 12–18 g/dL depending on sex; low values explain fatigue, pallor and tachycardia.
WBC 5,000–10,000: high suggests infection, very low means neutropenic precautions. Platelets 150,000–400,000: low means bleeding precautions.
Practice questions
1. A client taking digoxin has a potassium of 3.1 mEq/L and reports nausea. Which action is priority?
Answer and rationale
Correct: B. Hypokalemia increases digoxin toxicity risk, and nausea is an early toxicity sign. Hold the dose and notify the provider.
Frequently asked questions
Do I need to memorize every lab value?
No. Master the decision-driving values first — potassium, sodium, glucose, BUN, creatinine, CBC — and learn the rest through practice questions.
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Sources
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