Cheatography
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High-yield NCLEX-RN lab values with normal ranges, critical values, and what to do — one-page rapid review.
Electrolytes
Sodium (Na+) |
135–145 mEq/L — critical <120 or >160 |
Potassium (K+) |
3.5–5.0 mEq/L — critical <2.5 or >6.0; check ECG (peaked T / U waves) |
Calcium (Ca2+) |
8.5–10.5 mg/dL — Trousseau's/Chvostek's signs when low |
Magnesium (Mg2+) |
1.5–2.5 mEq/L — low Mg worsens refractory hypokalemia |
Phosphorus |
2.5–4.5 mg/dL |
Chloride (Cl−) |
98–106 mEq/L |
Kidney & Metabolic
BUN |
10–20 mg/dL — rises with dehydration and renal failure |
Creatinine |
0.6–1.2 mg/dL — best single indicator of renal function |
BUN:Creatinine ratio |
~10:1 normal; high ratio suggests prerenal cause (dehydration) |
Glucose (fasting) |
70–100 mg/dL — critical <40 or >400 |
HbA1c |
<5.7% normal; ≥6.5% diabetes |
Hematology & Coagulation
WBC |
5,000–10,000/mm³ — high = infection/inflammation |
RBC |
M 4.5–5.5 / F 4.0–5.0 million/mm³ |
Hemoglobin |
M 14–18 / F 12–16 g/dL — critical <5 or >20 |
Hematocrit |
M 40–54% / F 36–46% — roughly 3× hemoglobin |
Platelets |
150,000–400,000/mm³ — critical <20,000 (bleeding risk) |
PT |
11–12.5 sec — monitors warfarin with INR |
INR |
0.8–1.1 normal; therapeutic on warfarin 2.0–3.0 — critical >5 |
aPTT |
30–40 sec — monitors heparin; therapeutic 1.5–2.5× normal |
ABGs
pH |
7.35–7.45 |
PaCO₂ |
35–45 mmHg — respiratory component (up = acidosis) |
HCO₃⁻ |
22–26 mEq/L — metabolic component |
PaO₂ |
80–100 mmHg; SaO₂ 95–100% |
Quick read: match the abnormal value to its system — CO₂ abnormal = respiratory, HCO₃ abnormal = metabolic; pH tells acidosis vs alkalosis |
Therapeutic Drug Levels (NCLEX favorites)
Digoxin |
0.8–2.0 ng/mL — toxicity: vision changes, anorexia, arrhythmias; check K+ first |
Lithium |
0.6–1.2 mEq/L — toxicity >1.5; maintain hydration and salt intake |
Phenytoin (Dilantin) |
10–20 mcg/mL — toxicity: nystagmus, ataxia, slurred speech |
Theophylline |
10–20 mcg/mL — toxicity: tachycardia, seizures |
Critical Values — Act First
K+ <2.5 or >6.0, Na+ <120 or >160, platelets <20,000, Hgb <5, glucose <40 or >400, INR >5 |
NCLEX rule: unstable airway/breathing/circulation beats lab values — assess the patient, then report critical labs immediately |
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