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.
💡 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 or >20 g/dL | Low: anemia, bleeding. High: polycythemia, dehydration |
| Hematocrit (Hct) | M: 42-52% F: 37-47% |
<21% or >60% | Percentage of RBCs in blood. Trends with hemoglobin |
| White Blood Cells (WBC) | 5,000-10,000/μL | <2,000 or >30,000/μL | Low: immunocompromised. High: infection, leukemia |
| Platelets | 150,000-450,000/μL | <50,000 or >1,000,000/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 | <120 or >160 mEq/L | Low: seizures, confusion. High: neurologic symptoms |
| Potassium (K+) | 3.5-5.0 mEq/L | <3.0 or >5.0 mEq/L | Critical for cardiac function. Monitor ECG changes |
| Chloride (Cl-) | 98-107 mEq/L | <80 or >115 mEq/L | Follows sodium. Important for acid-base balance |
| CO2 (Bicarbonate) | 22-28 mEq/L | <15 or >40 mEq/L | Acid-base status. Low: acidosis. High: alkalosis |
| Glucose | 70-100 mg/dL (fasting) | <50 or >400 mg/dL | Low: hypoglycemia. High: diabetes complications |
| BUN | 10-20 mg/dL | >100 mg/dL | Kidney function. Elevated in dehydration, renal disease |
| Creatinine | 0.6-1.2 mg/dL | >4.0 mg/dL | Best indicator of kidney function |
🫀 Liver Function Tests
| Lab Test | Normal Range | Critical Values | Clinical Significance |
|---|---|---|---|
| ALT (SGPT) | 7-56 U/L | >1000 U/L | Liver-specific enzyme. Elevated in hepatitis, toxicity |
| AST (SGOT) | 10-40 U/L | >1000 U/L | Found in liver, heart, muscle. Less specific than ALT |
| Bilirubin (Total) | 0.3-1.2 mg/dL | >15 mg/dL | High: jaundice, liver disease, hemolysis |
| Albumin | 3.5-5.0 g/dL | <2.0 g/dL | Low: malnutrition, liver disease, kidney disease |
| Alkaline Phosphatase | 44-147 U/L | >1000 U/L | Elevated in liver disease, bone disorders |
❤️ Cardiac Markers
| Lab Test | Normal Range | Critical Values | Clinical Significance |
|---|---|---|---|
| Troponin I | <0.04 ng/mL | >0.04 ng/mL | Gold standard for MI diagnosis. Peaks 12-24 hours |
| CK-MB | 0-6.3 ng/mL | >6.3 ng/mL | Heart-specific enzyme. Peaks 18-24 hours post-MI |
| BNP | <100 pg/mL | >400 pg/mL | Heart failure marker. Higher = worse HF |
| D-Dimer | <0.50 mg/L | >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 | >30 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 | >70 seconds | 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 >7.60 | <7.35: acidosis. >7.45: alkalosis |
| PaCO2 | 35-45 mmHg | <20 or >70 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 | <60 mmHg | Oxygenation status. <60: respiratory failure |
| O2 Saturation | 95-100% | <90% | Percentage of hemoglobin saturated with oxygen |
🔬 Additional Critical Labs
| Lab Test | Normal Range | Critical Values | Clinical Significance |
|---|---|---|---|
| Magnesium (Mg2+) | 1.3-2.1 mEq/L | <1.0 or >3.0 mEq/L | Low: seizures, arrhythmias. Often depleted with K+ |
| Phosphorus | 3.0-4.5 mg/dL | <1.0 or >9.0 mg/dL | Inverse relationship with calcium |
| Calcium (Total) | 9.0-10.5 mg/dL | <7.0 or >12.0 mg/dL | Low: tetany, seizures. High: kidney stones, arrhythmias |
| Lactic Acid | 0.5-2.2 mEq/L | >4.0 mEq/L | High: tissue hypoxia, sepsis, shock |
| Ammonia | 10-80 mcg/dL | >200 mcg/dL | High: hepatic encephalopathy |
| Digoxin Level | 0.8-2.0 ng/mL | >2.0 ng/mL | Narrow therapeutic window. Toxicity: nausea, arrhythmias |
| Thyroid Stimulating Hormone (TSH) | 0.4-4.0 mU/L | <0.1 or >20 mU/L | High: hypothyroid. Low: hyperthyroid |
| Hemoglobin A1C | <5.7% | >10% | 3-month glucose control. Goal <7% for diabetics |
🎯 Quick Reference: When to Call the Doctor STAT
Immediate Notification Required:
- K+ <3.0 or >5.0 mEq/L
- Glucose <50 or >400 mg/dL
- Hgb <7 g/dL
- Platelets <50,000/μL
- INR >5.0
- Any positive troponin
Monitor Closely:
- Na+ <130 or >150 mEq/L
- Creatinine rising trend
- WBC <4,000 or >15,000/μL
- pH <7.30 or >7.50
- Lactic acid >2.2 mEq/L
- BUN/Creatinine ratio >20:1
💡 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!
⚠️ 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.