Reference — Labs & Diagnostics
Normal Laboratory Values: RT Quick Reference
A bedside quick reference of normal adult laboratory values for the respiratory therapist — the complete blood count, electrolytes and metabolic panel, coagulation studies, lactate, the arterial blood gas, and the cardiac biomarkers.
Written by Apex Respiratory Editorial Team
Educational use only. This material supports respiratory therapy education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional protocols, or physician orders. Always follow facility policies and current provider orders, and verify calculations independently before clinical use.
Overview
Respiratory therapists read laboratory data alongside the arterial blood gas to build a complete clinical picture — a falling hemoglobin explains hypoxemia at a normal SaO₂, a rising lactate flags hypoperfusion before the blood pressure drops, and the metabolic panel anchors every acid–base interpretation. The tables below collect the normal adult reference ranges you will reach for most often at the bedside, grouped by panel for quick scanning.
These are typical adult values. Reference ranges are laboratory- and method-specific, so always confirm against the ranges printed by the reporting laboratory before acting on a result — see the clinical notes below.
Complete Blood Count (CBC)
| Test | Normal adult range | Notes |
|---|---|---|
| White blood cells (WBC) | 4.5–11 ×10⁹/L (4,500–11,000/µL) | Leukocytosis with infection, stress, steroids; leukopenia with overwhelming sepsis. |
| Neutrophils | 40–70% of WBC | A left shift (bands) suggests acute bacterial infection. |
| Lymphocytes | 20–40% | Lymphopenia is common in critical illness and viral pneumonia. |
| Eosinophils | 1–4% | Eosinophilia (>5% or >0.5 ×10⁹/L) supports asthma, allergy, or eosinophilic disease. |
| Hemoglobin (Hgb) | Male 13.5–17.5 g/dL; female 12.0–16.0 g/dL | Drives O₂ carrying capacity; anemia worsens tissue hypoxia at any SaO₂. |
| Hematocrit (Hct) | Male 41–53%; female 36–46% | Roughly three times the hemoglobin; rises with dehydration and chronic hypoxemia. |
| Platelets | 150–400 ×10⁹/L (150,000–400,000/µL) | Thrombocytopenia raises bleeding risk for line placement and procedures. |
Electrolytes & Metabolic Panel
| Test | Normal adult range | Notes |
|---|---|---|
| Sodium (Na⁺) | 135–145 mEq/L | Hyponatremia is common in heart failure and SIADH; affects mental status. |
| Potassium (K⁺) | 3.5–5.0 mEq/L | Hypokalemia from β₂-agonists and diuretics; both extremes cause arrhythmias. |
| Chloride (Cl⁻) | 98–106 mEq/L | Moves with sodium and bicarbonate; informs the acid–base picture. |
| Total CO₂ (HCO₃⁻) | 22–28 mEq/L | The metabolic-panel bicarbonate; runs slightly higher than the ABG-calculated HCO₃⁻. |
| Anion gap | 8–12 mEq/L | A high gap signals lactic acidosis, ketoacidosis, toxins, or renal failure. |
| BUN | 7–20 mg/dL | Rises with dehydration, GI bleeding, and renal impairment. |
| Creatinine | 0.6–1.2 mg/dL | The best routine marker of renal function; guides drug and contrast decisions. |
| Glucose (fasting) | 70–100 mg/dL | Hyperglycemia is common in critical illness; <40 mg/dL is a critical value. |
| Calcium | 8.5–10.5 mg/dL | Interpret with albumin; ionized calcium matters most in critical illness. |
| Magnesium | 1.5–2.5 mg/dL | Low magnesium provokes arrhythmias and refractory bronchospasm. |
| Phosphate | 2.5–4.5 mg/dL | Hypophosphatemia can weaken the diaphragm and impair weaning. |
| Albumin | 3.5–5.0 g/dL | Low albumin shifts the corrected calcium and signals chronic illness. |
Arterial Blood Gas (for orientation)
| Test | Normal adult range | Notes |
|---|---|---|
| pH | 7.35–7.45 | The first decision point in acid–base interpretation. |
| PaCO₂ | 35–45 mmHg | The respiratory component; high in hypoventilation, low in hyperventilation. |
| HCO₃⁻ | 22–26 mEq/L | The metabolic component; calculated from pH and PaCO₂. |
| PaO₂ | 80–100 mmHg | Falls with age and altitude; interpret against the FiO₂. |
| SaO₂ | 95–100% | Arterial oxygen saturation; should track the SpO₂ when perfusion is adequate. |
| Base excess | −2 to +2 mEq/L | Quantifies the metabolic acid–base deviation from normal. |
Coagulation Studies
| Test | Normal adult range | Notes |
|---|---|---|
| PT | 11–13.5 s | Reflects the extrinsic pathway; prolonged by warfarin and liver disease. |
| INR | ~0.8–1.1 | Standardized PT; the warfarin therapeutic target is usually 2.0–3.0. |
| aPTT | 25–35 s | Reflects the intrinsic pathway; monitors unfractionated heparin. |
| Fibrinogen | 200–400 mg/dL | An acute-phase reactant; falls in DIC and massive hemorrhage. |
| D-dimer | <500 ng/mL FEU (negative) | A sensitive but nonspecific marker; a negative result helps exclude PE. |
Perfusion & Cardiac Biomarkers
| Test | Normal adult range | Notes |
|---|---|---|
| Lactate | 0.5–2.2 mmol/L | Marker of tissue hypoperfusion; >2 is abnormal and ≥4 signals severe hypoperfusion. |
| BNP | <100 pg/mL | Values <100 make heart failure unlikely; >400 supports it. |
| NT-proBNP | Age-dependent cutoffs | Use the assay's age-stratified thresholds rather than a single number. |
| Troponin | Assay-specific | Normal at or below the 99th-percentile upper reference limit for the assay. |
Clinical Notes
- Reference ranges are laboratory- and method-specific — always use the reporting laboratory’s own ranges rather than a memorized number.
- Many ranges differ by age, sex, and pregnancy; hemoglobin, hematocrit, and the BNP-family cutoffs are the most common examples.
- The metabolic-panel total CO₂ runs slightly higher than the ABG-calculated HCO₃⁻ because it includes dissolved CO₂ and carbamino compounds — expect a small discrepancy between the two.
- Critical (panic) values demand immediate action and direct communication — for example, K⁺ >6.0 or <2.5 mEq/L, glucose <40 mg/dL, or platelets <20,000/µL.
Related Resources
Sources
- Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021. Reference ranges; laboratory assessment.
- National Board for Respiratory Care. Therapist Multiple-Choice Examination Detailed Content Outline. NBRC; 2024. Patient data evaluation and recommendations.