NCLEX lab values: the chart worth memorizing
The NCLEX rarely asks you to recite a range. It asks what a value means and what you do next. So this chart pairs every major value with the action it triggers. Values below are standard adult reference ranges — the same ones used throughout the NCLEX Decoded system.
Electrolytes
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| Lab | Normal range | When it's off, think… |
|---|
| Sodium (Na⁺) | 135–145 mEq/L | Low: confusion, seizures (correct slowly). High: thirst, neuro changes, give free water as ordered. |
| Potassium (K⁺) | 3.5–5.0 mEq/L | The cardiac electrolyte. High: peaked T waves → cardiac emergency. Low: digoxin toxicity risk, ileus. |
| Chloride (Cl⁻) | 98–106 mEq/L | Moves with sodium; part of acid–base interpretation. |
| Calcium (total) | 9.0–10.5 mg/dL | Low: tetany, Chvostek/Trousseau. High: stones, bones, groans, moans — think parathyroid/malignancy. |
| Magnesium (Mg²⁺) | 1.3–2.1 mEq/L | Low with low potassium that won't correct. High (on Mg infusion): watch respirations, reflexes. |
| Phosphorus | 3.0–4.5 mg/dL | Inverse to calcium; rises in renal failure. |
| BUN | 10–20 mg/dL | Rises with dehydration and renal failure. |
| Creatinine | 0.5–1.2 mg/dL | The truest renal marker; doubles ≈ half of kidney function lost. |
| Glucose (fasting) | 70–105 mg/dL | Below 70: treat hypoglycemia first, ask questions later (15 g fast carbs, recheck in 15). |
| HbA1c | < 5.7% normal; ≥ 6.5% diabetes | Target for most diabetic clients: below 7%. |
Arterial blood gases
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| Value | Normal | Reading it |
|---|
| pH | 7.35–7.45 | Below 7.35 acidotic, above 7.45 alkalotic. The pH names the disorder. |
| PaCO₂ | 35–45 mmHg | The respiratory lever — moves opposite the pH. |
| HCO₃⁻ | 22–28 mEq/L | The metabolic lever — moves with the pH. |
| PaO₂ | 80–100 mmHg | Oxygenation, interpreted with the clinical picture. |
Method that never fails: look at pH first, then decide whether CO₂ (respiratory) or HCO₃ (metabolic) moved in the direction that explains it, then check whether the other value is compensating.
Hematology & coagulation
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| Lab | Normal range | Exam angle |
|---|
| Hemoglobin | M 14–18 · F 12–16 g/dL | Low = anemia/bleeding; watch trends after surgery. |
| Hematocrit | M 42–52% · F 37–47% | Roughly 3× the hemoglobin. |
| WBC | 5,000–10,000 /mm³ | High: infection/inflammation. Low: the chemo client who can't fight — neutropenic precautions. |
| Platelets | 150,000–400,000 /mm³ | Below 50,000: bleeding precautions. Below 20,000: spontaneous bleeding risk. |
| PT / INR | PT 11–12.5 s · INR 0.9–1.2 | Warfarin therapy target INR usually 2.0–3.0. |
| aPTT | 30–40 s | Heparin monitored by aPTT, classically 1.5–2.5× the control value. |
Therapeutic drug levels
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| Drug | Therapeutic range | Toxicity headline |
|---|
| Digoxin | 0.5–2.0 ng/mL | Nausea, visual changes, dysrhythmias — and hypokalemia makes it worse. |
| Lithium | 0.6–1.2 mEq/L (maintenance) | Coarse tremor, confusion, polyuria; sodium and hydration move the level. |
| Phenytoin | 10–20 mcg/mL | Nystagmus, ataxia, slurred speech. |
| Valproic acid | 50–100 mcg/mL | Liver and platelets — monitor both. |
| Theophylline | 10–20 mcg/mL | Tachycardia, tremor, seizures when high. |
Study tip: don't memorize this page in one sitting. The Core Bundle's flashcard decks turn every row into a card, and the questions make you use the values — the way the exam will.
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