50 Must-Know Lab Values for Nurses
Your comprehensive reference guide to essential laboratory values in nursing practice
Essential Lab Values Every Nurse Must Know
Master these 50 critical lab values to excel in clinical practice, pass the NCLEX, and provide safe patient care. This reference guide includes normal ranges, critical values, and clinical significance for the most important laboratory tests in nursing.
Important Note: Normal lab value ranges may vary slightly between laboratories, institutions, and testing methods. Always refer to your facility's specific reference ranges and consult with healthcare providers for patient-specific interpretations.
💡 Pro Tip: Bookmark this page and review these values regularly. Consider printing a pocket-sized version for clinical rotations!
🩸 Complete Blood Count (CBC)
| Lab Test | Normal Range | Critical Values | Clinical Significance |
|---|---|---|---|
| Hemoglobin (Hgb) | M: 14-18 g/dL F: 12-16 g/dL |
≤7.0 g/dL | Low: anemia, bleeding. High: polycythemia, dehydration |
| Hematocrit (Hct) | M: 42-52% F: 37-47% |
<25% or >65% | Percentage of RBCs in blood. Trends with hemoglobin |
| White Blood Cells (WBC) | 5,000-10,000/μL | ≤1,500 or ≥100,000/μL | Low: immunocompromised. High: infection, leukemia |
| Platelets | 150,000-450,000/μL | ≤25,000/μL | Low: bleeding risk. High: clotting risk |
| Neutrophils | 50-70% | ≤1,000/μL (ANC) | First line immune defense. Low = infection risk |
⚡ Basic Metabolic Panel (BMP)
| Lab Test | Normal Range | Critical Values | Clinical Significance |
|---|---|---|---|
| Sodium (Na+) | 136-145 mEq/L | <125 or >155 mmol/L | Low: seizures, confusion. High: neurologic symptoms |
| Potassium (K+) | 3.5-5.0 mEq/L | <3.0 or >6.0 mmol/L | Critical for cardiac function. Monitor ECG changes |
| Chloride (Cl-) | 98-107 mEq/L | — | Follows sodium. Important for acid-base balance |
| CO2 (Bicarbonate) | 23-29 mEq/L | <15 or >40 mmol/L | Acid-base status. Low: acidosis. High: alkalosis |
| Glucose | 70-100 mg/dL (fasting) | <60 or >400 mg/dL | Low: hypoglycemia. High: diabetes complications |
| BUN | 10-20 mg/dL | — | Kidney function. Elevated in dehydration, renal disease |
| Creatinine | 0.6-1.2 mg/dL | ≥1.5 mg/dL (1d-4wk) ≥2.0 (5wk-23mo) ≥2.5 (2-11yr) ≥3.0 (12-15yr) ≥10.0 (16-17yr) |
Best indicator of kidney function. Critical values vary by age |
🫀 Liver Function Tests
| Lab Test | Normal Range | Critical Values | Clinical Significance |
|---|---|---|---|
| ALT (SGPT) | 7-56 U/L | — | Liver-specific enzyme. Elevated in hepatitis, toxicity |
| AST (SGOT) | 10-40 U/L | — | Found in liver, heart, muscle. Less specific than ALT |
| Bilirubin (Total) | 0.3-1.2 mg/dL | ≥15.0 mg/dL (<1yr) | High: jaundice, liver disease, hemolysis. Neonatal values differ significantly |
| Albumin | 3.5-5.0 g/dL | — | Low: malnutrition, liver disease, kidney disease |
| Alkaline Phosphatase | 44-147 U/L | — | Elevated in liver disease, bone disorders |
❤️ Cardiac Markers
| Lab Test | Normal Range | Critical Values | Clinical Significance |
|---|---|---|---|
| Troponin I | <0.04 ng/mL | ≥0.05 μg/L (POCT) | Gold standard for MI diagnosis. Peaks 12-24 hours |
| CK-MB | 0-6.3 ng/mL | — | Heart-specific enzyme. Peaks 18-24 hours post-MI |
| BNP | <100 pg/mL | — | Heart failure marker. Higher = worse HF |
| D-Dimer | <0.50 mg/L | — | High: possible clot (PE, DVT). High sensitivity, low specificity |
🩸 Coagulation Studies
| Lab Test | Normal Range | Critical Values | Clinical Significance |
|---|---|---|---|
| PT (Prothrombin Time) | 11-13 seconds | — | Monitors warfarin therapy. Extrinsic pathway |
| INR | 0.8-1.1 | ≥5.0 | Standardized PT. Target 2-3 for most anticoagulation |
| PTT (aPTT) | 25-35 seconds | ≥60 sec | Monitors heparin therapy. Intrinsic pathway |
🫁 Arterial Blood Gas (ABG)
| Lab Test | Normal Range | Critical Values | Clinical Significance |
|---|---|---|---|
| pH | 7.35-7.45 | <7.20 or >7.55 | <7.35: acidosis. >7.45: alkalosis |
| PaCO2 | 35-45 mmHg | <25 or >65 mmHg | Respiratory component. Inverse relationship with pH |
| HCO3- (Bicarbonate) | 22-26 mEq/L | <15 or >40 mEq/L | Metabolic component. Direct relationship with pH |
| PaO2 | 80-100 mmHg | <40 mmHg | Oxygenation status. <60: respiratory failure |
| O2 Saturation | 95-100% | — | Percentage of hemoglobin saturated with oxygen |
🧬 Master ABG Interpretation
Practice with our interactive simulator, guided tutorial, and real patient scenarios
🔬 Additional Critical Labs
| Lab Test | Normal Range | Critical Values | Clinical Significance |
|---|---|---|---|
| Magnesium (Mg2+) | 1.3-2.1 mEq/L | <1.0 or >4.5 mg/dL | Low: seizures, arrhythmias. Often depleted with K+ |
| Phosphorus | 3.0-4.5 mg/dL | <1.0 mg/dL | Inverse relationship with calcium |
| Calcium (Total) | 9.0-10.5 mg/dL | <6.5 or >13.5 mg/dL | Low: tetany, seizures. High: kidney stones, arrhythmias |
| Lactic Acid | 0.5-2.2 mEq/L | >3.9 mmol/L | High: tissue hypoxia, sepsis, shock |
| Ammonia | 10-80 mcg/dL | ≥100 mcmol/L (<1yr) ≥200 mcmol/L (≥1yr) |
High: hepatic encephalopathy. Lower threshold for infants |
| Carbon Monoxide | <2% | ≥20% | High: carbon monoxide poisoning. Life-threatening at >20% |
| Osmolality | 275-295 mOsm/kg | ≤190 or ≥390 mOsm/kg | Measures blood concentration. Low: overhydration. High: dehydration |
| Digoxin Level | 0.8-2.0 ng/mL | >2.0 μg/L | Narrow therapeutic window. Toxicity: nausea, arrhythmias |
| Thyroid Stimulating Hormone (TSH) | 0.4-4.0 mU/L | — | High: hypothyroid. Low: hyperthyroid |
| Hemoglobin A1C | <5.7% | — | 3-month glucose control. Goal <7% for diabetics |
🎯 Quick Reference: When to Call the Doctor STAT
Immediate Notification Required:
- K+ <3.0 or >6.0 mmol/L
- Glucose <60 or >400 mg/dL
- Hgb ≤7.0 g/dL
- Platelets ≤25,000/μL
- INR ≥5.0
- Troponin I ≥0.05 μg/L
- Carbon Monoxide ≥20%
Monitor Closely:
- Na+ <125 or >155 mmol/L
- WBC ≤1,500 or ≥100,000/μL
- pH <7.20 or >7.55
- Lactate >3.9 mmol/L
- PTT ≥60 seconds
- Calcium <6.5 or >13.5 mg/dL
- Osmolality ≤190 or ≥390 mOsm/kg
💡 5 Tips for Mastering Lab Values
Start with Critical Values
Focus on life-threatening values first: K+, glucose, Hgb, platelets. These require immediate action and are frequently tested on NCLEX.
Use Memory Tricks
Create mnemonics: "My K+ is 3.5-5, so I stay alive!" Connect numbers to familiar things: normal glucose (70-100) like a good test grade.
Understand the "Why"
Don't just memorize - understand what causes abnormal values. High WBC = infection, low Hgb = bleeding/anemia. This helps with NCLEX reasoning.
Practice with Real Cases
Review actual patient lab results during clinicals. Ask "What do these values tell me about this patient?" Connect labs to assessments and interventions.
Make Flashcards
Create cards with lab name on front, normal range + significance on back. Review daily during nursing school. Use our lab flashcards for practice!
📋 Pro Tip: Print this page and keep it in your nursing bag for quick reference!
📚 Continue Your Learning
📚 References & Sources ▼
Click to view 5 sources cited
⚠️ Important Disclaimer
This reference guide is for educational purposes only and should not replace clinical judgment, facility protocols, or provider orders. Normal ranges may vary by laboratory. Always verify critical values and follow your institution's policies for reporting abnormal results.