✨ Featured Lessons · Lesson 5 of 8 · 90 sec

The Lab Values You Must Recite in Your Sleep

🧪 The exam never prints the normal range next to the number. Here are the ones that decide the most questions, in the order they are tested.

💡 Key idea

Know these cold. Every question that includes a number assumes you do.

🧠 Why it matters

Sodium 135 to 145. Potassium 3.5 to 5.0. Calcium 9 to 10.5. Magnesium 1.5 to 2.5. Glucose 70 to 99 fasting. BUN 10 to 20. Creatinine 0.6 to 1.2. Hemoglobin 12 to 16 women, 14 to 18 men. Platelets 150,000 to 400,000. White cells 5,000 to 10,000. INR 2 to 3 on warfarin. aPTT 1.5 to 2.5 times control on heparin. Digoxin 0.5 to 2.0. Lithium 0.6 to 1.2. Phenytoin 10 to 20. A1c under 7 for most adults with diabetes. pH 7.35 to 7.45, PaCO2 35 to 45, HCO3 22 to 26.

🏥 In the real world

📝 Write them on an index card. Read it at every red light for a week. On exam day, a question says 'potassium 3.1' and your brain says 'low, watch for U waves and digoxin' before you finish the sentence. That reflex is worth more than any strategy.

📌 Takeaways

Electrolytes: Na 135–145, K 3.5–5.0, Ca 9–10.5, Mg 1.5–2.5
Kidney: BUN 10–20, creatinine 0.6–1.2; blood: Hgb 12–18, platelets 150–400k, WBC 5–10k
Drugs: digoxin 0.5–2.0, lithium 0.6–1.2, phenytoin 10–20; INR 2–3 on warfarin

✅ Test yourself

Which value is outside the normal range?

Potassium 5.8 mEq/L
Sodium 140 mEq/L
Calcium 9.6 mg/dL
Magnesium 2.0 mEq/L

Answer: A · Potassium 5.8 mEq/L

Potassium above 5.0 is hyperkalemia; the other values are normal.

A client taking lithium has a level of 1.9 mEq/L. How should the nurse interpret this?

Below therapeutic range
Toxic; assess for tremor, vomiting and ataxia
Therapeutic
Normal for maintenance therapy of bipolar disorder

Answer: B · Toxic; assess for tremor, vomiting and ataxia

The therapeutic range is 0.6 to 1.2; above about 1.5 the client is at risk for toxicity.

Start this lesson free →

NCLEX-style questions, XP and streaks in the app. No sign-up needed.