The NCLEX Lab Values You Actually Need to Memorize (2026 Guide)

nursepassacademy

Jul 23

2 min read

Every semester a student shows me a stack of index cards with forty reference ranges on them, and every semester I say the same thing: the NCLEX is not testing whether you memorized a chemistry textbook. It is testing whether an abnormal number changes what you do next.

These are the values worth knowing cold — and, more importantly, the action each one demands.

The Electrolytes That Decide Questions

Potassium 3.5–5.0 mEq/L: the most-tested number on the exam. High or low, think cardiac — ECG changes, muscle weakness, and medications you hold or give.
Sodium 135–145 mEq/L: think neuro. Confusion, seizures, and safety precautions are the cues.
Calcium 9.0–10.5 mg/dL: low calcium brings tingling and positive Trousseau and Chvostek signs.
Magnesium 1.3–2.1 mEq/L: low magnesium and low potassium travel together — and both irritate the heart.

Coags and Drug Levels

INR: therapeutic on warfarin is generally 2 to 3. Higher means bleeding risk — hold and notify.
aPTT: on heparin, roughly 1.5 to 2 times control. Know protamine sulfate as the reversal.
Digoxin 0.5–2.0 ng/mL: toxicity cues are nausea, bradycardia, and visual changes.
Lithium 0.6–1.2 mEq/L: a narrow window — dehydration pushes it toxic.

ABGs Without the Panic

pH 7.35–7.45, PaCO2 35–45, HCO3 22–26. Match the abnormal value to the pH: if pH and CO2 move in opposite directions, the problem is respiratory; if pH and bicarb move in the same direction, it is metabolic. That single pattern answers most ABG questions on the exam.

Renal and Glucose

Creatinine 0.6–1.2 mg/dL: the kidney's report card — a rising creatinine means questions about holding nephrotoxic drugs and contrast dye.
BUN 10–20 mg/dL: rises with dehydration as well as kidney injury, so read it alongside creatinine.
Fasting glucose 70–100 mg/dL: below 70, treat first and ask questions later.

The Real Skill: The Next Action

Notice the pattern in every section above: the exam gives you a number so it can ask what you will do about it. Hold the med. Call the provider. Put the client on seizure precautions. When you review labs, always attach an action — that is the difference between memorizing and passing.

Want the whole set on one page? The Free NCLEX 2026 Starter Kit includes a printable cheat sheet plus 10 NGN practice questions. When you are ready to apply the numbers inside real case studies, the Complete NCLEX 2026 Library gives you 1,000 NGN questions across every body system.