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1.4 Laboratory Values & Diagnostic Data

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CRT/RRT Respiratory Therapist Exam Exam

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1 Introduction: NBRC TMC Exam Overview

NBRC TMC Exam Overview Credential Pathway: CRT to RRT Study Strategies for the TMC Exam Content Domains & Weight Distribution

2 Chapter 1: Patient Data Evaluation

1.1 Patient History & Physical Assessment 1.2 Diagnostic Procedures & ABG Interpretation 1.3 Hemodynamic Monitoring & Waveform Analysis 1.4 Laboratory Values & Diagnostic Data

3 Chapter 2: Airway Management & Oxygen Therapy

2.1 Airway Anatomy & Assessment 2.2 Airway Management Devices & Procedures 2.3 Oxygen Therapy Devices & Delivery 2.4 Humidification & Aerosol Therapy

4 Chapter 3: Mechanical Ventilation

3.1 Ventilation Fundamentals 3.2 Initial Ventilator Settings 3.3 Ventilator Monitoring & Waveform Analysis 3.4 Weaning & Liberation from Mechanical Ventilation

5 Chapter 4: Pharmacology & Equipment

4.1 Respiratory Pharmacology 4.2 Equipment & Troubleshooting 4.3 Specialty Procedures

6 Chapter 5: Infection Control, Ethics & Professional Practice

5.1 Infection Control & Prevention 5.2 Emergency Procedures & Resuscitation 5.3 Professional Practice & Ethics

1.4 Laboratory Values & Diagnostic Data

Key Takeaways Explain This Topic AI

CBC normals: WBC 5,000-10,000/mcL, Hgb 14-18 g/dL (male) or 12-16 (female), Hct 40-54% (male) or 36-46% (female), platelets 150,000-400,000.

Chronic hypoxemia drives secondary polycythemia (high RBC, Hgb, Hct) through erythropoietin — treat the hypoxemia, not the blood count.

BMP normals: 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 mg/dL.

Hypokalemia (K+ <3.5) causes metabolic alkalosis and respiratory-muscle weakness that impairs ventilator weaning; albuterol and diuretics are common causes.

BNP >100 pg/mL suggests heart failure and >500 strongly favors acute CHF — it separates cardiac from pulmonary dyspnea.

Troponin rises 3-6 hours after myocardial injury and is the most specific cardiac biomarker for MI.

D-dimer is highly SENSITIVE but not specific for PE/DVT; a negative result rules out PE in low-risk patients but a positive needs imaging.

Lactate >2 mmol/L signals tissue hypoperfusion and >4 mmol/L indicates severe sepsis or shock; sputum color narrows the likely organism.

Last updated: October 2026

Labs in Respiratory Decision-Making

ABGs dominate, but the TMC also expects you to read the CBC (complete blood count), BMP (basic metabolic panel), cardiac biomarkers, coagulation studies, lactate, and sputum results — because each one changes a respiratory plan.

Complete Blood Count

  • Component Normal Significance
  • WBC 5,000-10,000/mcL High: infection, inflammation, stress, steroids. Low: immunosuppression, chemotherapy
  • RBC M 4.5-5.5, F 4.0-5.0 million/mcL Low in anemia; high in polycythemia (chronic hypoxemia)
  • Hemoglobin M 14-18, F 12-16 g/dL Low Hgb cuts oxygen-carrying capacity even at SpO2 100%
  • Hematocrit M 40-54%, F 36-46% High in dehydration/polycythemia; low in anemia
  • Platelets 150,000-400,000/mcL Low = bleeding risk (DIC, HIT); high = inflammation

Clinical pearl: chronic hypoxemia (COPD, severe OSA) raises erythropoietin and produces secondary polycythemia — elevated RBC, Hgb, and Hct. The fix is correcting hypoxemia with oxygen, not phlebotomy alone. A WBC count with a left shift (rising bands) suggests acute bacterial infection.

Basic Metabolic Panel

  • Analyte Normal Respiratory Relevance
  • Na+ 136-145 mEq/L Hyponatremia (SIADH) causes confusion

K+ 3.5-5.0 mEq/L Low K+: alkalosis, muscle weakness, weaning failure, arrhythmia. High K+: peaked T waves, arrest

  • Cl- 98-106 mEq/L Low Cl- accompanies metabolic alkalosis (vomiting, NG suction)
  • CO2 (total) 22-26 mEq/L Mirrors HCO3; ties to the ABG metabolic component
  • BUN 7-20 mg/dL Up in renal failure, dehydration, GI bleed
  • Creatinine 0.7-1.3 mg/dL Most reliable renal marker
  • Glucose 70-100 mg/dL fasting Marked elevation with ketones = DKA (high-gap metabolic acidosis)

Potassium is the analyte the exam ties most often to respiratory care: hypokalemia weakens the diaphragm and accessory muscles, stalling ventilator weaning, and is frequently produced by the very beta-agonists and diuretics RTs administer.

Cardiac Biomarkers and Perfusion Markers

  • Marker Normal Elevated In Use
  • BNP <100 pg/mL Heart failure (>100 suggestive, >500 strong) Separate cardiac from pulmonary dyspnea
  • Troponin I/T <0.04 ng/mL MI, myocarditis Most specific MI marker; rises 3-6 h after onset
  • D-dimer <500 ng/mL PE, DVT, DIC, recent surgery Sensitive PE screen; not specific
  • Lactate <2 mmol/L Hypoperfusion, sepsis, shock >4 mmol/L = severe sepsis
  • Procalcitonin <0.1 ng/mL Bacterial infection Helps decide antibiotic start/stop

The paired logic to remember: BNP is sensitive AND fairly specific for heart failure , so a high value in a dyspneic patient points away from pure COPD; D-dimer is sensitive but NOT specific , so a negative result safely excludes PE in low pretest-probability patients while a positive only mandates imaging (CT pulmonary angiogram or V/Q scan). Troponin is the dedicated marker of myocardial injury and stays elevated for days after an infarction.

Sputum Analysis

  • Test Purpose Key Point
  • Gram stain Rapid bacterial class Gram-positive purple vs Gram-negative pink
  • Culture & sensitivity Identify organism + effective drug Takes 24-72 h; guides targeted antibiotics

AFB smear/culture Tuberculosis (M. tuberculosis) Positive AFB = airborne isolation, negative-pressure room, N95

Cytology Malignant cells Lung-cancer screening

Sputum color is a high-yield quick clue: yellow/green = bacterial infection; rust-colored = Streptococcus pneumoniae (pneumococcal) pneumonia ; pink and frothy = pulmonary edema; currant-jelly = Klebsiella; thick and tenacious = cystic fibrosis; frank blood = hemoptysis (TB, bronchiectasis, malignancy).

Coagulation Studies

  • Test Normal Monitors
  • PT 11-13.5 s Warfarin / extrinsic pathway
  • INR 0.8-1.2 (therapeutic 2.0-3.0 on warfarin) Standardized PT; >1.5 raises bleeding risk
  • PTT 25-35 s Heparin / intrinsic pathway
  • Fibrinogen 200-400 mg/dL Low in DIC and liver disease

These matter before invasive procedures the RT participates in — arterial puncture, bronchoscopy with biopsy, or line placement. The reversal agents differ and are commonly swapped as distractors: vitamin K (and FFP/PCC) reverses warfarin , while protamine sulfate reverses heparin — never substitute one for the other.

Tying Labs to Acid-Base and Ventilation

Laboratory values rarely stand alone on the exam; they are clues that confirm or refine an acid-base or oxygenation problem you have already begun to diagnose from the ABG. A few connections recur often enough to memorize:

A glucose of 200 mg/dL or more (or known diabetes) with ketones and a high anion gap points to diabetic ketoacidosis, the metabolic acidosis that drives Kussmaul respirations as the lungs blow off CO2 to compensate. Recognizing the lab pattern explains the breathing pattern at the bedside.

A low chloride with a low potassium and a high CO2 (bicarbonate) is the signature of a contraction metabolic alkalosis from vomiting, nasogastric suction, or loop diuretics — and it predicts the compensatory hypoventilation the ventilated patient may show.

A rising lactate with a normal or low blood pressure marks tissue hypoperfusion; a value above 4 mmol/L is a severe-sepsis trigger and a reason to escalate oxygen delivery and call for fluid or vasopressor support.

A rising BUN and creatinine flags renal failure, which both produces a metabolic acidosis (retained acids) and limits the kidney's ability to compensate for a respiratory disorder, so the patient leans harder on the lungs for acid-base control.

Using Labs to Decide and Recommend

The Patient Data Evaluation domain is graded heavily on whether you can move from a value to an action. A positive AFB smear is not just a microbiology result — it dictates a negative-pressure room and N95 respirators for staff. A platelet count of 40,000 or an INR of 3.5 changes whether arterial puncture or bronchoscopy with biopsy should proceed. A BNP of 700 in a wheezing patient steers therapy toward diuresis and afterload reduction rather than escalating bronchodilators.

On both the TMC and the clinical simulations, the highest-scoring response gathers the relevant lab, interprets it in context, and then recommends the specific intervention or precaution it implies.