Essential Lab Values
Normal ranges for CBC, BMP, CMP, coagulation, cardiac markers, liver, and thyroid panels with clinical significance.
Complete Blood Count (CBC)
| Test | Normal Range | Clinical Significance |
|---|---|---|
| WBC | 5,000 – 10,000/mm³ | Elevated: infection, leukemia. Low: immunosuppression, bone marrow failure |
| RBC (Male) | 4.7 – 6.1 million/mm³ | Low: anemia, hemorrhage. High: polycythemia |
| RBC (Female) | 4.2 – 5.4 million/mm³ | Low: anemia, hemorrhage. High: polycythemia |
| Hemoglobin (Male) | 14 – 18 g/dL | Low: anemia, bleeding. Critical < 7 g/dL |
| Hemoglobin (Female) | 12 – 16 g/dL | Low: anemia, bleeding. Critical < 7 g/dL |
| Hematocrit (Male) | 42% – 52% | Low: anemia. High: dehydration, polycythemia |
| Hematocrit (Female) | 37% – 47% | Low: anemia. High: dehydration, polycythemia |
| Platelets | 150,000 – 400,000/mm³ | Low: bleeding risk. High: clotting risk. Critical < 50,000 |
Basic Metabolic Panel (BMP)
| Test | Normal Range | Clinical Significance |
|---|---|---|
| Sodium (Na+) | 136 – 145 mEq/L | Low: hyponatremia (confusion, seizures). High: hypernatremia (thirst, agitation) |
| Potassium (K+) | 3.5 – 5.0 mEq/L | Low: dysrhythmias, weakness. High: peaked T waves, cardiac arrest. Critical < 3.0 or > 6.0 |
| Chloride (Cl−) | 98 – 106 mEq/L | Follows sodium trends |
| CO2 (Bicarbonate) | 22 – 26 mEq/L | Metabolic acid-base indicator |
| BUN | 10 – 20 mg/dL | Elevated: dehydration, renal failure, GI bleeding |
| Creatinine | 0.7 – 1.3 mg/dL | Most reliable indicator of kidney function |
| Glucose (Fasting) | 70 – 100 mg/dL | Low: hypoglycemia. High: DM, stress response. Critical < 50 or > 400 |
| Calcium (Ca2+) | 9.0 – 10.5 mg/dL | Low: tetany, Chvostek/Trousseau signs. High: lethargy, kidney stones |
Coagulation Studies
| Test | Normal Range | Clinical Significance |
|---|---|---|
| PT (Prothrombin Time) | 11 – 12.5 seconds | Monitors warfarin therapy |
| INR | 0.8 – 1.1 (Therapeutic: 2.0 – 3.0) | Standardized PT ratio. Target 2.5 – 3.5 for mechanical valves |
| aPTT | 30 – 40 seconds | Monitors heparin therapy. Therapeutic: 1.5 – 2.5 × control |
| D-Dimer | < 0.5 mcg/mL | Elevated: DVT, PE, DIC |
| Fibrinogen | 200 – 400 mg/dL | Low: DIC, liver disease |
Cardiac Markers
| Marker | Normal | Significance |
|---|---|---|
| Troponin I | < 0.04 ng/mL | Most specific for MI. Rises 3–6 hrs, peaks 14–18 hrs |
| CK-MB | < 5% total CK | Rises 4–6 hrs after MI. Useful for detecting reinfarction |
| BNP | < 100 pg/mL | Elevated in heart failure. Used to differentiate cardiac vs pulmonary dyspnea |
| Myoglobin | < 90 mcg/L | Earliest cardiac marker (1–3 hrs). Not specific to heart |
Liver Function Tests
| Test | Normal Range | Significance |
|---|---|---|
| ALT (SGPT) | 4 – 36 U/L | Most specific for liver damage |
| AST (SGOT) | 0 – 35 U/L | Liver and cardiac damage |
| Alkaline Phosphatase | 30 – 120 U/L | Elevated: biliary obstruction, bone disease |
| Total Bilirubin | 0.1 – 1.0 mg/dL | Elevated: jaundice, hemolysis, liver disease |
| Albumin | 3.5 – 5.0 g/dL | Low: malnutrition, liver disease, nephrotic syndrome |
| Ammonia | 10 – 80 mcg/dL | Elevated: hepatic encephalopathy. Give lactulose |
Thyroid Panel
| Test | Normal Range | Significance |
|---|---|---|
| TSH | 0.4 – 4.0 mIU/L | Primary screening test. High = hypothyroid, Low = hyperthyroid |
| Free T4 | 0.8 – 1.8 ng/dL | Low in hypothyroidism, High in hyperthyroidism |
| Free T3 | 2.3 – 4.2 pg/mL | Most active thyroid hormone |
Key Nursing Considerations
- Always verify critical values and notify the provider immediately
- Potassium: Never give IV push; always use an infusion pump; max 10 mEq/hr peripheral, 20 mEq/hr central
- INR/PT: Have vitamin K (phytonadione) available as antidote for warfarin
- aPTT: Have protamine sulfate available as antidote for heparin
- Troponin: Serial draws are needed (0, 3, 6 hours) to rule out MI