NCLEX Lab Values You Need to Memorize (Free Cheat Sheet)
Lab values are some of the easiest points on the NCLEX, if you know them cold.
They are also some of the most painful points to lose, because the exam will not give you a reference sheet. You are expected to look at a number and instantly know two things: is it normal, and if not, what do you do about it.
The good news is that you do not need to memorize hundreds of values. You need a focused core of about 20, plus an understanding of what each one means at the bedside. That is what this page gives you.
Below is a complete, organized cheat sheet of the lab values most likely to appear on your NCLEX-RN, with normal ranges and a quick note on why each one matters. Bookmark it, screenshot it, drill it.
And if you want to practice these values inside real NCLEX-style questions instead of just staring at a table, Mila Learning generates practice exams that put these numbers into clinical scenarios, which is how the real exam tests them.
A quick warning before the tables
Memorizing the number is only half the job.
The NCLEX almost never asks “what is the normal range for potassium.” Instead it gives you a patient, hands you a potassium of 6.4, shows you peaked T waves on the monitor, and asks what you do first. The number is the setup. The nursing action is the actual question.
So as you go through these, do not just memorize the range. Attach each value to its danger and its action. We have noted the most important ones for you.
Electrolytes
The big four (memorize these first)
| Lab | Normal range | Why it matters |
|---|---|---|
| Potassium (K+) | 3.5 to 5.0 mEq/L | The most tested value. Both high and low cause deadly cardiac arrhythmias. Peaked T waves suggest hyperkalemia. Give IV calcium gluconate first if ECG changes are present. |
| Sodium (Na+) | 135 to 145 mEq/L | Drives fluid balance and neuro status. Rapid correction is dangerous. Low sodium causes confusion and seizures. |
| Calcium (Ca2+) | 9.0 to 10.5 mg/dL | Low calcium causes Trousseau and Chvostek signs. High risk after thyroidectomy. Affects cardiac and neuromuscular function. |
| Magnesium (Mg2+) | 1.5 to 2.5 mEq/L | Watch in preeclampsia patients on mag sulfate. Toxicity causes loss of reflexes and respiratory depression. Antidote is calcium gluconate. |
| Chloride (Cl-) | 98 to 106 mEq/L | Moves with sodium and bicarbonate. Useful in acid-base interpretation. |
| Phosphorus | 3.0 to 4.5 mg/dL | Inverse relationship with calcium. Elevated in chronic kidney disease. |
Kidney function and glucose
Renal and metabolic
| Lab | Normal range | Why it matters |
|---|---|---|
| BUN | 7 to 20 mg/dL | Rises with dehydration and kidney impairment. Interpret alongside creatinine. |
| Creatinine | 0.6 to 1.2 mg/dL | The more specific marker of kidney function. Rising creatinine signals declining renal function and affects drug dosing. |
| GFR | > 90 mL/min | Best overall measure of kidney function. Below 60 for 3 months suggests chronic kidney disease. |
| Glucose (fasting) | 70 to 100 mg/dL | Below 70 is hypoglycemia, an emergency. Watch for insulin peak times. Above 200 with ketones suggests DKA. |
| Hemoglobin A1c | < 5.7% (normal) | Reflects 3-month glucose average. 6.5% or higher diagnoses diabetes. Goal under 7% for most diabetics. |
Complete blood count (CBC)
Hematology
| Lab | Normal range | Why it matters |
|---|---|---|
| Hemoglobin (Hgb) | 12 to 18 g/dL | Lower in women. Low values mean anemia and reduced oxygen-carrying capacity. |
| Hematocrit (Hct) | 36 to 52% | Roughly 3 times the hemoglobin. Rises with dehydration, falls with bleeding. |
| WBC | 5,000 to 10,000 /mm3 | High suggests infection. Low (neutropenia) means infection risk; consider protective isolation. |
| Platelets | 150,000 to 400,000 /mm3 | Below 50,000 raises bleeding risk; below 20,000 is critical. Watch in heparin-induced thrombocytopenia. |
Coagulation studies
Clotting (high-yield for anticoagulant questions)
| Lab | Normal range | Why it matters |
|---|---|---|
| PT | 11 to 13.5 seconds | Monitors warfarin. Prolonged means slower clotting. |
| INR (normal) | 0.8 to 1.1 | Standardized PT. Therapeutic range on warfarin is 2 to 3 (up to 3.5 for mechanical valves). |
| aPTT | 30 to 40 seconds | Monitors heparin. Therapeutic is 1.5 to 2.5 times the control value. |
| Platelets | 150,000 to 400,000 /mm3 | Also tracked during heparin therapy to catch HIT. |
Arterial blood gases (ABGs)
Acid-base balance
| Lab | Normal range | Why it matters |
|---|---|---|
| pH | 7.35 to 7.45 | Below 7.35 is acidosis, above 7.45 is alkalosis. The anchor of every ABG question. |
| PaCO2 | 35 to 45 mmHg | The respiratory component. High CO2 means respiratory acidosis. |
| HCO3 (bicarbonate) | 22 to 26 mEq/L | The metabolic component. Low bicarb means metabolic acidosis. |
| PaO2 | 80 to 100 mmHg | Oxygen level in arterial blood. Low values indicate hypoxemia. |
| O2 saturation | 95 to 100% | Below 90% needs intervention. Drives many priority and ABC questions. |
Therapeutic drug levels
Narrow therapeutic windows (heavily tested)
| Lab | Normal range | Why it matters |
|---|---|---|
| Digoxin | 0.5 to 2.0 ng/mL | Above 2.0 is toxic. Hold if apical pulse is below 60. Hypokalemia increases toxicity risk. |
| Lithium | 0.6 to 1.2 mEq/L | Above 1.5 is toxic (tremor, diarrhea, confusion). Maintain steady sodium and fluid intake. |
| Phenytoin (Dilantin) | 10 to 20 mcg/mL | Used for seizures. Toxicity causes nystagmus, ataxia, slurred speech. |
| Theophylline | 10 to 20 mcg/mL | Bronchodilator with a narrow window. Toxicity causes tachycardia and seizures. |
| Vancomycin (trough) | 10 to 20 mcg/mL | Monitor trough to avoid nephrotoxicity. Draw just before the next dose. |
How to actually memorize these (not just stare at them)
Reading a table once does almost nothing. Here is what works:
- Active recall. Cover the range and try to say it out loud before you check. The struggle to retrieve is what builds memory.
- Short daily reps. Ten minutes a day for two weeks beats one three-hour cram session.
- Attach the action. Do not memorize “digoxin 0.5 to 2.0.” Memorize “digoxin toxic above 2, hold if pulse under 60.” The action is what the exam tests.
- Apply in questions immediately. The moment a value feels familiar, use it in a practice question. Recognizing a number inside a clinical scenario is a completely different skill from reciting it on a flashcard.
Turn these values into real practice
A cheat sheet gets the numbers into your head. Practice questions get them into your hands.
Mila Learning lets you generate NCLEX-style practice exams on exactly the topics you are weak on, including fluid and electrolytes, ABGs, pharmacology, and lab interpretation. Every question comes with a full rationale, so you learn the reasoning, not just the answer.
You can pick a subject and start in seconds, or upload your own lecture notes for a personalized exam. The first sample exam is free, no credit card needed.
Frequently asked questions
How many lab values do I need to know for the NCLEX?
You do not need to memorize hundreds. Focus on the core set: the major electrolytes (potassium, sodium, calcium, magnesium), kidney function (BUN, creatinine), blood glucose, the CBC (hemoglobin, hematocrit, WBC, platelets), coagulation studies (PT, INR, aPTT), arterial blood gases, and therapeutic drug levels for digoxin and lithium. Knowing roughly 20 values cold covers the vast majority of lab-related questions.
Does the NCLEX give you a lab value reference sheet?
No. The NCLEX-RN does not provide a lab value reference during the exam. You are expected to recognize whether a value is normal, high, or low and to know the nursing action it requires. The exam rarely asks you to recall a number directly; it gives you a value and asks what you would do.
What lab values are most commonly tested on the NCLEX?
Potassium is the single most commonly tested value because abnormal levels cause life-threatening arrhythmias. Other high-yield values include digoxin and lithium therapeutic levels (often given just outside the safe range), INR for warfarin patients, ABG components for acid-base questions, and calcium for post-thyroidectomy patients. The NCLEX favors values tied to safety and the question “what do you do next.”
How do I memorize NCLEX lab values fast?
Use active recall, not passive rereading. Make flashcards with the lab name on one side and the range plus its clinical significance on the other. Drill them in short daily bursts, then immediately apply each value in practice questions, because the NCLEX tests application. Connecting a number to an action (for example, hold digoxin if apical pulse is below 60) is far stickier than the number alone.