✨ Featured Lessons · Lesson 5 of 8 · 90 sec
The Lab Values You Must Recite in Your Sleep
🧪 Many questions give a lab value with no normal range beside it, and even when a case exhibit shows one, knowing the range cold saves time. Here are the ones that decide the most questions.
💡 Key idea
Know these cold. Every question that includes a number assumes you do.
🧠 Why it matters
Sodium 135 to 145 mEq/L. Potassium 3.5 to 5.0 mEq/L. Calcium (total) 9 to 10.5 mg/dL. Magnesium 1.5 to 2.5 mEq/L. Glucose 70 to 99 mg/dL fasting. BUN 10 to 20 mg/dL. Creatinine 0.6 to 1.2 mg/dL. Hemoglobin 12 to 16 g/dL women, 14 to 18 g/dL men. Platelets 150,000 to 400,000/mm3. White cells 5,000 to 10,000/mm3. INR 2 to 3 on warfarin for most indications (higher for some mechanical valves). aPTT 1.5 to 2.5 times control on heparin. Digoxin 0.5 to 2.0 ng/mL. Lithium 0.6 to 1.2 mEq/L. Phenytoin 10 to 20 mcg/mL. A1c under 7% for most adults with diabetes. pH 7.35 to 7.45, PaCO2 35 to 45 mm Hg, HCO3 22 to 26 mEq/L.
🏥 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 12–16 (women), 14–18 (men), 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 the therapeutic range
- Above the therapeutic range
- Therapeutic
- Within the acute-mania therapeutic range
Answer: B · Above the therapeutic range
The maintenance range is 0.6 to 1.2 mEq/L, and acute mania is treated up to about 1.5. A level of 1.9 is toxic, so hold the dose, notify the provider, and assess for coarse tremor, vomiting, diarrhea, ataxia and confusion.
NCLEX-style questions, XP and streaks in the app. No sign-up needed.
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