Key Takeaways
- Critical potassium: < 2.5 or > 6.5 mEq/L requires immediate reporting
- Troponin is the most specific cardiac marker for myocardial infarction
- Therapeutic INR range for warfarin is typically 2.0-3.0; higher values increase bleeding risk
- Elevated BNP (> 100 pg/mL) suggests heart failure
- ABG interpretation: opposite direction of CO2 and pH = respiratory disorder
Last updated: January 2026
Laboratory Values
Understanding laboratory values is essential for monitoring patient status, recognizing abnormalities, and reporting significant findings. LPN/VNs must know normal ranges and the clinical significance of common lab tests.
Complete Blood Count (CBC)
| Test | Normal Range | Clinical Significance |
|---|---|---|
| RBC (Red Blood Cells) | M: 4.5-5.5; F: 4.0-5.0 million/μL | Oxygen-carrying capacity |
| Hemoglobin (Hgb) | M: 14-18; F: 12-16 g/dL | Oxygen-carrying protein; anemia indicator |
| Hematocrit (Hct) | M: 42-52%; F: 37-47% | Percentage of RBCs in blood volume |
| WBC (White Blood Cells) | 5,000-10,000/μL | Infection/immune response |
| Platelets | 150,000-400,000/μL | Clotting ability |
WBC Differential:
| Cell Type | Normal % | Increased In |
|---|---|---|
| Neutrophils | 55-70% | Bacterial infection, inflammation |
| Lymphocytes | 20-40% | Viral infection, leukemia |
| Monocytes | 2-8% | Chronic infection, inflammation |
| Eosinophils | 1-4% | Allergies, parasites |
| Basophils | 0.5-1% | Allergic reactions |
Clinical Concerns:
- Leukocytosis (> 10,000): Infection, inflammation, leukemia
- Leukopenia (< 5,000): Bone marrow suppression, immunocompromised
- Neutropenia (ANC < 1,500): High infection risk; < 500 is severe
- Thrombocytopenia (< 150,000): Bleeding risk; < 20,000 is critical
Coagulation Studies
| Test | Normal Range | Monitoring For |
|---|---|---|
| PT (Prothrombin Time) | 11-13 seconds | Warfarin therapy, liver function |
| INR | 1.0 (therapeutic: 2.0-3.0) | Warfarin therapy |
| aPTT | 25-35 seconds | Heparin therapy (1.5-2.5× normal) |
| Fibrinogen | 200-400 mg/dL | Clotting ability, DIC |
| D-dimer | < 500 ng/mL | DVT, PE, DIC |
Metabolic Panel
Basic Metabolic Panel (BMP)
| Test | Normal Range | Clinical Significance |
|---|---|---|
| Sodium (Na+) | 136-145 mEq/L | Fluid balance, neurological function |
| Potassium (K+) | 3.5-5.0 mEq/L | Cardiac function, muscle contraction |
| Chloride (Cl-) | 98-106 mEq/L | Acid-base balance |
| CO2 (Bicarbonate) | 23-29 mEq/L | Acid-base balance |
| BUN | 7-20 mg/dL | Kidney function, hydration |
| Creatinine | 0.6-1.2 mg/dL | Kidney function (most specific) |
| Glucose (Fasting) | 70-100 mg/dL | Diabetes management |
Critical Electrolyte Values:
| Electrolyte | Critical Low | Critical High |
|---|---|---|
| Potassium | < 2.5 mEq/L | > 6.5 mEq/L |
| Sodium | < 120 mEq/L | > 160 mEq/L |
| Calcium | < 6.0 mg/dL | > 13.0 mg/dL |
| Glucose | < 50 mg/dL | > 400 mg/dL |
Liver Function Tests (LFTs)
| Test | Normal Range | Significance |
|---|---|---|
| AST (SGOT) | 10-40 U/L | Liver damage, also heart/muscle |
| ALT (SGPT) | 7-56 U/L | Most specific for liver damage |
| ALP (Alkaline Phosphatase) | 44-147 U/L | Liver, bone disease |
| Total Bilirubin | 0.3-1.2 mg/dL | Liver function, hemolysis |
| Albumin | 3.5-5.0 g/dL | Liver synthesis, nutrition |
Cardiac Markers
| Marker | Normal | Rises | Peaks | Returns to Normal |
|---|---|---|---|---|
| Troponin I | < 0.03 ng/mL | 3-6 hours | 12-24 hours | 5-14 days |
| Troponin T | < 0.01 ng/mL | 3-6 hours | 12-24 hours | 10-14 days |
| CK-MB | 0-5 ng/mL | 4-8 hours | 12-24 hours | 2-3 days |
| BNP | < 100 pg/mL | N/A | N/A | N/A |
BNP (B-type Natriuretic Peptide):
- Elevated in heart failure
-
100 pg/mL suggests CHF
- Used to distinguish cardiac from pulmonary causes of dyspnea
Thyroid Function
| Test | Normal Range | Interpretation |
|---|---|---|
| TSH | 0.4-4.0 mU/L | Primary screening test |
| T4 (Free) | 0.8-1.8 ng/dL | Active thyroid hormone |
| T3 | 80-200 ng/dL | Active thyroid hormone |
Interpretation:
- Hypothyroid: High TSH, low T4/T3
- Hyperthyroid: Low TSH, high T4/T3
Arterial Blood Gases (ABGs)
| Parameter | Normal Range |
|---|---|
| pH | 7.35-7.45 |
| PaCO2 | 35-45 mmHg |
| HCO3 | 22-26 mEq/L |
| PaO2 | 80-100 mmHg |
Quick ABG Interpretation:
- Check pH: < 7.35 = acidosis; > 7.45 = alkalosis
- Check CO2: If CO2 and pH move opposite directions = respiratory
- Check HCO3: If HCO3 and pH move same direction = metabolic
- Determine if compensated (pH normalized) or uncompensated
Test Your Knowledge
A patient's potassium level is 6.8 mEq/L. What action should the LPN/VN take?
A
B
C
D
Test Your Knowledge
Which laboratory test is most specific for diagnosing a myocardial infarction?
A
B
C
D
Test Your Knowledge
A patient on warfarin therapy has an INR of 4.5. What does this indicate?
A
B
C
D