NCLEX-RN Study Guide
NCLEX Lab Values You Need to Memorize
By the NCLEX Up Team
6 min read · Reviewed for accuracy · Updated May 29, 2026
Lab values show up all over the NCLEX-RN — in pharmacology, fluid and electrolytes, and prioritization questions. You don't need to memorize every value in the textbook, but these are the ones worth knowing cold. Reference ranges vary slightly by lab; these are the commonly taught NCLEX ranges.
Electrolytes
| Lab | Normal range |
|---|---|
| Sodium (Na+) | 135–145 mEq/L |
| Potassium (K+) | 3.5–5.0 mEq/L |
| Calcium (Ca2+) | 9.0–10.5 mg/dL |
| Magnesium (Mg2+) | 1.5–2.5 mEq/L |
| Chloride (Cl−) | 95–105 mEq/L |
| Phosphorus | 2.5–4.5 mg/dL |
Potassium is the one to watch hardest. Both low (hypokalemia) and high (hyperkalemia) can be life-threatening and are heavily tested — especially with digoxin and renal patients.
Arterial blood gases (ABGs)
| Value | Normal range |
|---|---|
| pH | 7.35–7.45 |
| PaCO2 | 35–45 mmHg |
| HCO3 (bicarb) | 22–26 mEq/L |
| PaO2 | 80–100 mmHg |
| O2 saturation | 95–100% |
Complete blood count (CBC)
| Lab | Normal range |
|---|---|
| WBC | 5,000–10,000 /mm³ |
| RBC | 4.2–6.1 million/mm³ |
| Hemoglobin (Hgb) | Female 12–16, Male 14–18 g/dL |
| Hematocrit (Hct) | Female 37–47%, Male 42–52% |
| Platelets | 150,000–400,000 /mm³ |
Coagulation
| Lab | Normal / therapeutic |
|---|---|
| INR | 0.8–1.1 (therapeutic on warfarin: 2–3) |
| aPTT | 30–40 sec (therapeutic on heparin: 1.5–2.5× normal) |
| PT | 11–12.5 sec |
Therapeutic drug levels
| Drug | Therapeutic range |
|---|---|
| Digoxin | 0.5–2.0 ng/mL |
| Lithium | 0.6–1.2 mEq/L |
| Dilantin (phenytoin) | 10–20 mcg/mL |
Drug levels are a favorite NCLEX trap: they'll give you a value and ask whether to hold, give, or report. Memorize the narrow ones — digoxin and lithium toxicity show up constantly.
Other commonly tested values
| Lab | Normal range |
|---|---|
| BUN | 10–20 mg/dL |
| Creatinine | 0.6–1.2 mg/dL |
| Fasting glucose | 70–110 mg/dL |
| HbA1c | < 5.7% (normal) |
| Total cholesterol | < 200 mg/dL |
Drill lab-value questions with rationales
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This article is for study purposes only and is not medical advice. NCLEX Up is not affiliated with the NCSBN or the NCLEX. Always verify exam details with the official NCSBN candidate bulletin and confirm clinical values with your nursing program.
Frequently asked questions
What lab values are most important for the NCLEX?
Electrolytes (especially potassium and sodium), ABGs, and therapeutic drug levels like digoxin and lithium are tested most heavily. These connect directly to high-priority, life-threatening scenarios.
Do I need to memorize exact lab ranges for the NCLEX?
You should know the common ranges well enough to recognize when a value is dangerously abnormal and decide whether to hold a drug, give it, or report it. The NCLEX tests your clinical judgment around the value, not just the number.