Key Takeaways
- CBC: Normal WBC 5,000-10,000/mcL (elevated in infection/inflammation), Hgb 12-16 g/dL (females) or 14-18 g/dL (males), Hct 36-46% (females) or 40-54% (males)
- BMP includes Na+ (136-145), K+ (3.5-5.0), Cl- (98-106), CO2 (22-26), BUN (7-20), Creatinine (0.7-1.3), Glucose (70-100)
- Coagulation: INR 0.8-1.2 normal, >1.5 significant bleeding risk; PTT 25-35 seconds normal
- D-dimer elevated in PE, DVT, DIC, post-surgery; sensitive but not specific
- BNP >100 pg/mL suggests heart failure; >500 pg/mL highly suggestive of acute CHF
- Troponin I or T elevation indicates myocardial injury (MI); rises 3-6 hours after onset
- Sputum analysis includes Gram stain, culture and sensitivity, and cytology
- Lactate >2 mmol/L suggests tissue hypoperfusion; >4 mmol/L indicates severe sepsis/shock
Laboratory Values & Diagnostic Data
While ABGs are the primary laboratory test for respiratory therapists, the TMC exam also tests your knowledge of other laboratory values that influence respiratory care decisions. Understanding these values helps you identify comorbidities, assess treatment responses, and recognize complications.
Complete Blood Count (CBC)
| Component | Normal Range | Clinical Significance |
|---|---|---|
| WBC (White Blood Cells) | 5,000-10,000/mcL | Elevated: infection, inflammation, stress, corticosteroids. Decreased: immunosuppression, chemotherapy |
| RBC (Red Blood Cells) | Male: 4.5-5.5 million/mcL, Female: 4.0-5.0 million/mcL | Decreased in anemia; increased in polycythemia (chronic hypoxemia) |
| Hemoglobin (Hgb) | Male: 14-18 g/dL, Female: 12-16 g/dL | Low Hgb reduces oxygen-carrying capacity even with normal SpO2 |
| Hematocrit (Hct) | Male: 40-54%, Female: 36-46% | Elevated in dehydration and polycythemia; low in anemia and overhydration |
| Platelets | 150,000-400,000/mcL | Low: bleeding risk (DIC, heparin therapy). High: infection, inflammation |
Clinical Pearl: Chronic hypoxemia (COPD, sleep apnea) stimulates erythropoietin production, leading to secondary polycythemia (elevated RBC, Hgb, Hct). This is the body's attempt to increase oxygen-carrying capacity.
Basic Metabolic Panel (BMP)
| Electrolyte | Normal Range | Respiratory Significance |
|---|---|---|
| Sodium (Na+) | 136-145 mEq/L | Hyponatremia can cause altered mental status; SIADH |
| Potassium (K+) | 3.5-5.0 mEq/L | Hypokalemia: metabolic alkalosis, weakness, arrhythmias. Hyperkalemia: peaked T waves, cardiac arrest |
| Chloride (Cl-) | 98-106 mEq/L | Low Cl-: metabolic alkalosis (vomiting, NG suction) |
| CO2 (total) | 22-26 mEq/L | Reflects HCO3 level; correlates with ABG metabolic component |
| BUN | 7-20 mg/dL | Elevated in renal failure, dehydration, GI bleeding |
| Creatinine | 0.7-1.3 mg/dL | Most reliable marker of renal function |
| Glucose | 70-100 mg/dL (fasting) | Elevated in DKA (metabolic acidosis), stress response, corticosteroid use |
Cardiac Biomarkers
| Marker | Normal | Elevated In | Clinical Use |
|---|---|---|---|
| BNP (B-type Natriuretic Peptide) | <100 pg/mL | Heart failure (>100 suggestive, >500 highly suggestive) | Distinguish cardiac from pulmonary dyspnea |
| Troponin I/T | <0.04 ng/mL | Myocardial infarction, myocarditis | Detect myocardial injury; rises 3-6 hours post-MI |
| D-dimer | <500 ng/mL | PE, DVT, DIC, post-surgical | Sensitive screening for PE/DVT; not specific |
| Lactate | <2 mmol/L | Tissue hypoperfusion, sepsis, shock | >4 mmol/L = severe sepsis indicator |
| Procalcitonin | <0.1 ng/mL | Bacterial infection/sepsis | Helps guide antibiotic therapy decisions |
Sputum Analysis
| Test | Purpose | Key Findings |
|---|---|---|
| Gram stain | Rapid identification of bacteria | Gram-positive (purple) vs. Gram-negative (pink) |
| Culture & Sensitivity | Identifies specific organism and effective antibiotics | Results take 24-72 hours; guides targeted therapy |
| AFB smear/culture | Tests for tuberculosis (Mycobacterium tuberculosis) | Positive AFB = airborne precautions required |
| Cytology | Screens for malignant cells | Lung cancer screening in high-risk patients |
| Color assessment | Quick clinical assessment | Yellow/green: infection; rust: pneumococcal pneumonia; pink/frothy: pulmonary edema; bloody: hemoptysis |
Coagulation Studies
| Test | Normal Range | Clinical Significance |
|---|---|---|
| PT (Prothrombin Time) | 11-13.5 seconds | Monitors warfarin therapy; extrinsic pathway |
| INR | 0.8-1.2 (therapeutic: 2.0-3.0 on warfarin) | Standardized PT ratio; >1.5 = significant bleeding risk |
| PTT (Partial Thromboplastin Time) | 25-35 seconds | Monitors heparin therapy; intrinsic pathway |
| Fibrinogen | 200-400 mg/dL | Low in DIC, liver disease |
A COPD patient has an Hgb of 19 g/dL and Hct of 58%. This is MOST likely caused by:
A patient presents with dyspnea and a BNP level of 650 pg/mL. This result is MOST suggestive of:
Which laboratory test is the MOST sensitive screening tool for pulmonary embolism?
Which of the following conditions would cause an ELEVATED lactate level? (Select all that apply)
Select all that apply
A patient on heparin therapy has a PTT of 85 seconds (normal 25-35). This result indicates:
Rust-colored sputum is MOST commonly associated with which condition?
A patient has a K+ level of 2.8 mEq/L (normal 3.5-5.0). This is significant for respiratory care because hypokalemia can cause: