Lab Values Quick Reference (NCLEX)

Electrolytes

• Sodium (Na⁺)

  • Normal range: $135\text{–}145\ \text{mEq/L}$
  • Hypernatremia (High Na⁺): dehydration, Cushing’s syndrome, diabetes insipidus (DI).
  • Manifestations: thirst, neurological irritability, seizures (>$160\ \text{mEq/L}$ = critical).
  • Hyponatremia (Low Na⁺): syndrome of inappropriate antidiuretic hormone (SIADH), fluid overload, renal failure.
  • Risk: seizures when $<120\ \text{mEq/L}$.

• Potassium (K⁺)

  • Normal range: $3.5\text{–}5.0\ \text{mEq/L}$
  • Hyperkalemia: renal failure, tissue destruction (burns, trauma), metabolic acidosis.
  • Cardiac arrest risk if $>6.5\ \text{mEq/L}$.
  • Hypokalemia: loop/thiazide diuretics, vomiting, diarrhea, alkalosis.
  • Arrhythmia risk if $<2.5\ \text{mEq/L}$ (flattened T-waves, U-waves).
  • NCLEX Critical Alert: $K^+<2.5$ or $>6.5\ \text{mEq/L}$ = cardiac emergency.

• Calcium (Ca²⁺)

  • Normal range: $8.5\text{–}10.5\ \text{mg/dL}$
  • Hypercalcemia: hyperparathyroidism, malignancy with bone metastasis.
  • S/S: "bones, stones, groans, psychiatric overtones".
  • Hypocalcemia: hypoparathyroidism, vitamin D deficiency, pancreatitis.
  • Chvostek’s & Trousseau’s signs; tetany.

• Magnesium (Mg²⁺)

  • Normal range: $1.5\text{–}2.5\ \text{mEq/L}$
  • Hypermagnesemia: renal failure, excessive antacid/laxative ingestion.
  • Hyporeflexia, bradycardia, hypotension.
  • Hypomagnesemia: chronic alcoholism, malnutrition, diuretics.
  • Torsades de pointes, neuromuscular irritability.

• Chloride (Cl⁻)

  • Normal range: $95\text{–}105\ \text{mEq/L}$
  • High: dehydration, metabolic acidosis (follows Na⁺).
  • Low: vomiting, metabolic alkalosis.

• Phosphate (PO₄³⁻)

  • Normal range: $2.5\text{–}4.5\ \text{mg/dL}$
  • Hyperphosphatemia: renal failure, tumor lysis.
  • Hypophosphatemia: alcoholism, malnutrition, re-feeding.

Renal Function

• Blood Urea Nitrogen (BUN)

  • Normal: $10\text{–}20\ \text{mg/dL}$
  • Elevated in kidney dysfunction, dehydration, GI bleed, high protein diet.

• Creatinine

  • Normal: $0.6\text{–}1.2\ \text{mg/dL}$
  • Best single indicator of glomerular filtration; rises with impaired renal function.

• Glomerular Filtration Rate (GFR)

  • Normal: >90\ \text{mL/min/1.73\,m^2}
  • $<60$ for >3 months = chronic kidney disease; $<15$ = kidney failure (dialysis).

Glucose

• Fasting Plasma Glucose
  • Normal: $70\text{–}110\ \text{mg/dL}$
  • Hyperglycemia: diabetes mellitus, Cushing’s, stress response.
  • Critical $>400\ \text{mg/dL}$ (risk DKA/HHS).
  • Hypoglycemia: insulin overdose, Addison’s disease, starvation.
  • Critical $<50\ \text{mg/dL}$ (neuro-glycopenic symptoms, seizure).
  • NCLEX Critical Alert: BG $<50$ or $>400\ \text{mg/dL}$ = emergency.

Hematology

• White Blood Cells (WBC)

  • Normal: $5{,}000\text{–}10{,}000\ /\text{mm}^3$
  • Leukocytosis = infection/inflammation; leukopenia = immunosuppression (e.g., chemo).

• Red Blood Cells (RBC)

  • Normal: $4.2\text{–}6.0\ \text{million}/\mu L$
  • Low = anemia, hemorrhage, bone-marrow suppression.

• Hemoglobin (Hgb)

  • Female: $12\text{–}16\ \text{g/dL}$
  • Male: $14\text{–}18\ \text{g/dL}$

• Hematocrit (Hct)

  • Female: $36\text{–}48\%$
  • Male: $42\text{–}52\%$
  • Rough rule: $Hct\approx 3\times Hgb$.

• Platelets (Plt)

  • Normal: $150{,}000\text{–}400{,}000\ /\text{mm}^3$
  • Risk of spontaneous bleeding when $<50{,}000$ (critical NCLEX alert).

Coagulation Studies

• Prothrombin Time (PT): $11\text{–}14\ \text{sec}$ (extrinsic pathway).
• International Normalized Ratio (INR)
  • Normal: $0.8\text{–}1.2$
  • Therapeutic on warfarin: $2\text{–}3$ (valve replacement may require $2.5\text{–}3.5$).
  • NCLEX Critical Alert: $INR>4$ = high bleeding risk -> hold warfarin, vitamin K.
• Activated Partial Thromboplastin Time (aPTT)
  • Normal: $25\text{–}35\ \text{sec}$
  • Heparin therapy goal: $1.5\text{–}2\times$ baseline (≈$45\text{–}70\ \text{sec}$).

Liver Function

• Albumin

  • Normal: $3.5\text{–}5.0\ \text{g/dL}$
  • Low in chronic liver disease, nephrotic syndrome, malnutrition; causes peripheral edema, ascites due to ↓ oncotic pressure.

• Total Bilirubin

  • Normal: $0.1\text{–}1.2\ \text{mg/dL}$
  • Elevated in hepatocellular damage, biliary obstruction, hemolysis (jaundice).

Cardiac Marker

• B-type Natriuretic Peptide (BNP)
  • Normal: $<100\ \text{pg/mL}$
  • $>100$ suggests heart failure; higher values correlate with severity.

Arterial Blood Gases (ABGs)

• pH: $7.35\text{–}7.45$
  • $<7.35$ = acidemia; $>7.45$ = alkalemia.
• PaCO₂: $35\text{–}45\ \text{mmHg}$
  • High = respiratory acidosis (hypoventilation); low = respiratory alkalosis (hyperventilation).
• HCO₃⁻: $22\text{–}26\ \text{mEq/L}$
  • Low = metabolic acidosis; high = metabolic alkalosis.
• PaO₂: $80\text{–}100\ \text{mmHg}$ (age dependent).
• SpO₂: $95\text{–}100\%$
  • Hypoxemia triggers: COPD, PE, high altitude.

Consolidated NCLEX Critical Alerts

• $K^+<2.5$ or $>6.5\ \text{mEq/L}$ → Cardiac dysrhythmia/arrest.
• $Na^+<120$ or $>160\ \text{mEq/L}$ → Cerebral edema or dehydration → Seizure precautions.
• $INR>4$ → Hold warfarin; assess for bleeding; give vitamin K.
• Blood glucose $<50$ or $>400\ \text{mg/dL}$ → Treat hypoglycemia with dextrose or hyperglycemia (DKA/HHS) with insulin/fluids.
• Platelets $<50{,}000$ → Spontaneous bleeding risk; avoid IM injections, aspirin.