NCLEX® lab values to know.
The normal ranges nursing students actually get tested on, grouped by system, each paired with the nursing action behind the number. Learn the value and the response together.
Reference ranges vary slightly by lab and textbook. These are common adult values used in nursing programs. Always verify against your own course materials and your facility's lab reference sheet.
Electrolytes
| Lab | Normal range | Why it matters |
|---|---|---|
| Sodium (Na+) | 135 to 145 mEq/L | Low sodium can cause confusion and seizures; correct slowly to avoid cerebral shifts. |
| Potassium (K+) | 3.5 to 5.0 mEq/L | Both low and high potassium cause fatal dysrhythmias. Never IV push potassium. |
| Chloride (Cl-) | 98 to 106 mEq/L | |
| Calcium (total) | 9.0 to 10.5 mg/dL | Low calcium brings Trousseau and Chvostek signs; watch the airway. |
| Magnesium (Mg2+) | 1.3 to 2.1 mEq/L | Low magnesium often drives refractory low potassium and calcium. |
| Phosphorus | 3.0 to 4.5 mg/dL |
Arterial Blood Gases (ABG)
| Lab | Normal range | Why it matters |
|---|---|---|
| pH | 7.35 to 7.45 | Below 7.35 is acidosis, above 7.45 is alkalosis. Start every ABG here. |
| PaCO2 | 35 to 45 mmHg | The respiratory component. High CO2 with low pH means respiratory acidosis. |
| HCO3- | 22 to 26 mEq/L | The metabolic component. Low HCO3 with low pH means metabolic acidosis. |
| PaO2 | 80 to 100 mmHg | |
| SaO2 | 95 to 100% |
Renal Function
| Lab | Normal range | Why it matters |
|---|---|---|
| BUN | 10 to 20 mg/dL | Rises with dehydration and kidney injury; read alongside creatinine. |
| Creatinine | 0.6 to 1.2 mg/dL | The more specific kidney marker. A doubling signals acute kidney injury. |
| GFR | greater than 90 mL/min | Drops define chronic kidney disease staging. |
Glucose
| Lab | Normal range | Why it matters |
|---|---|---|
| Fasting glucose | 70 to 100 mg/dL | Below 70 is hypoglycemia; treat with fast-acting carbs, then recheck. |
| Hemoglobin A1c | less than 5.7% (normal) | Reflects roughly 3 months of control; 6.5% or higher indicates diabetes. |
Complete Blood Count (CBC)
| Lab | Normal range | Why it matters |
|---|---|---|
| WBC | 5,000 to 10,000 /mcL | Low counts mean neutropenic precautions; high suggests infection. |
| Hemoglobin (Hgb) | 12 to 16 g/dL (F), 14 to 18 g/dL (M) | Low levels mean less oxygen delivery; watch for fatigue and tachycardia. |
| Hematocrit (Hct) | 37 to 47% (F), 42 to 52% (M) | |
| Platelets | 150,000 to 400,000 /mcL | Below 50,000 raises bleeding risk; below 20,000 is critical. |
Coagulation
| Lab | Normal range | Why it matters |
|---|---|---|
| PT | 11 to 12.5 seconds | |
| INR | 0.8 to 1.1 (therapeutic 2 to 3 on warfarin) | Guides warfarin dosing; a high INR means bleeding risk, antidote is vitamin K. |
| aPTT | 30 to 40 seconds (therapeutic 1.5 to 2x on heparin) | Guides heparin dosing; antidote is protamine sulfate. |
Cardiac Markers
| Lab | Normal range | Why it matters |
|---|---|---|
| Troponin | less than 0.03 ng/mL | The most specific marker of myocardial injury; a rise points to MI. |
| BNP | less than 100 pg/mL | Rises with fluid overload in heart failure. |
Therapeutic Drug Levels
| Lab | Normal range | Why it matters |
|---|---|---|
| Digoxin | 0.5 to 2.0 ng/mL | Toxicity brings nausea, visual halos, and bradycardia; hold for a low pulse. |
| Lithium | 0.6 to 1.2 mEq/L | Narrow window; above 1.5 is toxic. Dehydration and low sodium raise levels. |
| Phenytoin | 10 to 20 mcg/mL | |
| Vancomycin (trough) | 10 to 20 mcg/mL | Draw the trough right before the next dose to guide dosing. |
Don't memorize the chart. Practice the response.
A lab value on a flashcard is a number you can recognize but not always recall under pressure. The NCLEX® rarely asks you to state a range. It asks what you do when a client's potassium is 6.1 mEq/L or their INR is 5.2. Practice questions that put an abnormal value in front of you and make you act, and the ranges stick because they are attached to a decision.
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Lab values, answered
- What lab values do I need to memorize for the NCLEX®?
- Focus on the values tied to a nursing action: sodium, potassium, calcium, and magnesium; the ABG set (pH, PaCO2, HCO3); BUN and creatinine; fasting glucose; WBC, hemoglobin, and platelets; INR and aPTT; troponin and BNP; and the narrow-window drug levels like digoxin and lithium. Knowing the number matters less than knowing what to do when it is out of range.
- Are these the exact ranges my exam will use?
- Reference ranges vary slightly by lab and textbook. The ranges here are the common adult values used in nursing programs. Always verify against your own course materials and your facility's lab reference sheet, since your instructor grades to the ranges they teach.
- How should I study lab values without just memorizing a chart?
- Learn each value with its consequence. A potassium of 6.0 mEq/L is not a number to recite, it is peaked T waves and a client you act on now. Practicing questions that make you respond to an abnormal value builds the recall that a flashcard alone cannot.
- Which lab values show up most on the NCLEX®?
- Potassium, sodium, the ABG set, INR and aPTT for anticoagulants, and the therapeutic drug levels (digoxin, lithium, vancomycin) are heavily tested because each one drives a clear safety decision. Expect questions that ask what you do first when the value is critical.