Lab values appear on nearly every NCLEX exam. You need to know normal ranges, recognize critical values, understand what abnormalities mean clinically, and know what nursing action to take.
Complete Blood Count (CBC)
| Value | Normal Range | Low means | High means |
|---|---|---|---|
| WBC | 4,500–11,000/μL | Immunosuppression, bone marrow suppression | Infection, inflammation, leukemia |
| Hemoglobin (F) | 12–16 g/dL | Anemia — assess for hypoxia, fatigue | Polycythemia, dehydration |
| Hemoglobin (M) | 14–18 g/dL | Anemia | Polycythemia |
| Hematocrit (F) | 37–47% | Anemia, overhydration | Dehydration, polycythemia |
| Platelets | 150,000–400,000/μL | <50,000: bleeding risk; <20,000: spontaneous bleeding | Thrombocytosis — clotting risk |
Basic Metabolic Panel (BMP)
| Value | Normal Range | Critical values |
|---|---|---|
| Sodium (Na+) | 135–145 mEq/L | <120 or >160: neuro symptoms, seizure risk |
| Potassium (K+) | 3.5–5.0 mEq/L | <2.5 or >6.5: cardiac dysrhythmia risk |
| Glucose | 70–110 mg/dL (fasting) | <40: hypoglycemic emergency; >400: DKA/HHS concern |
| BUN | 10–20 mg/dL | Elevated: renal insufficiency, dehydration, GI bleed |
| Creatinine | 0.6–1.2 mg/dL | >10: severe renal failure; rising trend = AKI |
| Calcium | 8.5–10.5 mg/dL | <7: tetany, Trousseau's; >12: confusion, stones |
Coagulation Studies
| Value | Normal | Clinical note |
|---|---|---|
| PT/INR | PT: 11–13 sec; INR: 0.8–1.1 | Monitors warfarin. Therapeutic INR for most indications: 2.0–3.0 |
| aPTT | 25–35 seconds | Monitors heparin therapy. Therapeutic: 1.5–2.5× normal (60–100 sec) |
Cardiac Markers
- Troponin I/T: Most specific for myocardial injury. Rises 4–6 hours after MI, peaks 24 hours, remains elevated 7–10 days. Single most important cardiac marker for NCLEX.
- CK-MB: Rises 3–6 hours, peaks 18–24 hours, returns to normal in 72 hours. Useful for detecting reinfarction.
- BNP/NT-proBNP: Elevated in heart failure. Higher level = more severe failure = poorer prognosis.
Arterial Blood Gas (ABG) Interpretation
Normal values: pH 7.35–7.45, PaCO2 35–45, HCO3 22–26, PaO2 80–100.
Step 1: Is the pH acidotic (<7.35) or alkalotic (>7.45)?
Step 2: Is CO2 the cause (respiratory) or is HCO3 the cause (metabolic)?
Step 3: Is there compensation?
| Disorder | pH | PaCO2 | HCO3 | Common cause |
|---|---|---|---|---|
| Respiratory acidosis | ↓ | ↑ | Normal/↑ | COPD, sedation, hypoventilation |
| Respiratory alkalosis | ↑ | ↓ | Normal/↓ | Anxiety, hyperventilation, altitude |
| Metabolic acidosis | ↓ | Normal/↓ | ↓ | DKA, AKI, sepsis, lactic acidosis |
| Metabolic alkalosis | ↑ | Normal/↑ | ↑ | Vomiting, loop diuretics, antacid overuse |
Most common NCLEX lab value question type: A patient receiving a medication — what lab value do you monitor? Know: ACE inhibitors → potassium and creatinine; loop diuretics → potassium; lithium → lithium level and sodium; methotrexate → CBC and LFTs; aminoglycosides → BUN, creatinine, and hearing.
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