NCLEX Lab Values Cheat Sheet — The 15 Values You Must Know [Free Reference]

Lab values are the single most heavily tested subject on the NCLEX. Walk into any nursing student's study group and you'll hear the same question: "What's the normal potassium again?"

Memorizing your core lab values does more than help you answer a question — it builds confidence. When you see a sodium of 132 in an NGN case study and immediately recognize it as hyponatremia, you're not guessing anymore. You're thinking like a nurse. And that clinical instinct is exactly what the NCSBN is testing.

This cheat sheet covers the 15 lab values you will absolutely see on exam day — grouped by category with normal ranges, critical values, and memory tricks so they actually stick.

The 15 Essential NCLEX Lab Values

### Electrolytes

• **Sodium (Na⁺):** 135-145 mEq/L — Critical: <120 or >160 — (Remember: "Salt is NAsty above 145")
• **Potassium (K⁺):** 3.5-5.0 mEq/L — Critical: <2.5 or >6.5 — (Remember: "K⁺ is Kritical — hold K if >5.0")
• **Calcium (Ca²⁺):** 8.5-10.5 mg/dL — Critical: <7.0 or >13.0 — (Remember: "Calcium is 8 to 10 — bones need calcium")
• **Magnesium (Mg²⁺):** 1.5-2.5 mEq/L — Critical: <1.0 or >5.0 — (Remember: "Mag 1.5 to 2.5 — magically relaxed")
• **Chloride (Cl⁻):** 95-105 mEq/L — Critical: <80 or >115

### Hematology

• **Hemoglobin (Hgb):** M: 13.5-17.5, F: 12.0-16.0 g/dL — Critical: <7.0 or >20
• **Hematocrit (Hct):** M: 38-50%, F: 34-46% — Critical: <20% or >60%
• **Platelets:** 150,000-450,000/mm³ — Critical: <50,000 or >1,000,000
• **WBC:** 4,500-11,000/mm³ — Critical: <500 or >50,000
• **INR:** 0.9-1.2 — Therapeutic on warfarin: 2.0-3.0 — Critical: >5.0

### Blood Gases (ABGs)

• **pH:** 7.35-7.45 — (Remember: 7.35-7.45 = alive and thriving)
• **PaCO₂:** 35-45 mmHg — (Remember: CO₂ is the respiratory side — up = acidosis)
• **HCO₃⁻:** 22-26 mEq/L — (Remember: bicarb is the metabolic side)
• **PaO₂:** 80-100 mmHg — Critical: <55
• **SaO₂:** 95-100%

### Coags

• **aPTT:** 25-35 seconds — Therapeutic on heparin: 1.5-2.5x control

How NCLEX Tests Lab Values

Here's a truth that surprises most students: the NCLEX almost never asks "What is the normal range for potassium?" as a standalone question. Instead, they embed lab values directly into NGN case studies and expect you to recognize abnormal results and intervene — without being told the range first.

**Example scenario:** A 68-year-old patient on a potassium-sparing diuretic for CHF has a serum potassium of 5.6 mEq/L. The NGN case study gives you the lab result and asks: "Which intervention should the nurse implement first?" If you know normal K⁺ is 3.5-5.0, you'll immediately flag 5.6 as hyperkalemia and look for the answer about holding potassium, checking for ECG changes (tall T waves), and notifying the provider. If you don't know the range, you might pick the wrong intervention and lose partial credit on that section.

This pattern repeats across every NGN case study — lab values are the hidden signal that tells you what's happening clinically. Memorizing them turns vague scenarios into obvious answers.

Quick Memory Tricks

These mnemonics will save you on exam day:

• **"MECK"** — Magnesium (Mg) and Calcium (Ca) are opposites. High Mg = low Ca. Low Mg = high Ca. Think of them as a see-saw.
• **"K⁺ is KING"** — Potassium controls the heart. High K = tall, peaked T waves (the KING wears a tall crown). Low K = U waves (the crown fell off).
• **"ROME"** — Respiratory Opposite, Metabolic Equal. For ABG interpretation: In respiratory disorders, pH and PaCO₂ move opposite directions. In metabolic disorders, pH and HCO₃⁻ move the same direction.

Download the Printable PDF

Bookmark this page and use it during your daily NCLEX practice. For a printable PDF version with all 15 lab values plus 20 NGN practice questions to apply them, subscribe to free weekly NCLEX tips: [Send me the lab values PDF](mailto:chapmanalexandermello@gmail.com?subject=Send%20me%20the%20lab%20values%20PDF).

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