Clinical Laboratory Studies

Chapter 7: Clinical Laboratory Studies

Overview of Clinical Laboratory Tests

• Clinical laboratory tests are critical for various medical purposes including:

  • Diagnosis: Determining presence or absence of disease.

  • Treatment: Assessing therapeutic effectiveness and adjusting treatments.

  • Monitoring: Observing disease progression or resolution.

  • Prevention: Identifying risk factors and preventing disease occurrence.

Disciplines within Clinical Laboratory Studies

• Microbiology

• Hematology

• Immunology

• Transfusion Medicine

• Clinical Chemistry

• Molecular Diagnostics

Clinical Laboratory Case Study

• Patient Presentation: A patient presents with:

  • Fine crackles in all lung regions bilaterally.

  • Mild work of breathing (WOB).

  • Vital Signs:

    • Heart Rate (HR): 112

    • Blood Pressure (BP): 164/98

    • Oxygen Saturation (SpO2): 92% on room air (RA)

    • Respiratory Rate (RR): 28

  • Assessment: Requires evaluation of lab parameters to guide management.

  • Importance of knowing lab values highlighted: facilitates accurate diagnosis and treatment decisions.

Blood Composition

• Blood consists of:

  • Cells (45%):

    • White Blood Cells (WBC; leukocytes)

    • Red Blood Cells (RBC; erythrocytes)

    • Platelets (thrombocytes)

  • Plasma (55%):

    • Composed of water and soluble substances.

Normal Laboratory Values

• WBC Count: 4.5 - 11.5 x 10^9/L

• RBC Count:

  • Males: 4.6 - 6 x 10^12/L

  • Females: 4 - 5.4 x 10^12/L

• Platelet Count: 150,000 - 450,000 /µL

Hematology Tests

• Two main categories of hematology tests are:

  • General Hematology Tests: Used to evaluate the normal and abnormal cells in the blood.

  • Coagulation Studies: Assess the blood clotting capability.

• Importance of Blood Testing: Crucial for understanding blood pathologies and clotting disorders.

Complete Blood Count (CBC)

• Purpose: Determines the circulating counts of red and white blood cells; evaluates size and hemoglobin content of RBCs.

White Blood Cell (WBC) Count

• Normal WBC composition:

  • Distribution important:

    • Neutrophils: 40% - 70% (most prevalent)

    • Eosinophils: 0% - 6%

    • Basophils: 0% - 1%

    • Lymphocytes: 20% - 45%

    • Monocytes: 2% - 10%

• WBC information can indicate infections and immune response status.

Neutrophils

• Function: Majority of WBCs, crucial for fighting infections.

  • Produced in bone marrow, circulate until needed:

    • Migrate to inflamed tissues to perform phagocytosis.

    • Lifespan of approximately 10 days.

Other Types of White Blood Cells

• Eosinophils:

  • Role in allergic reactions; makes up 0% - 6% of WBCs.

• Basophils:

  • Comprises 0% - 1%, involved in inflammatory responses.

• Lymphocytes:

  • Fight viral, fungal infections; two subclasses: B and T cells.

    • B cells produce antibodies.

    • T cells destroy infected cells.

• Monocytes:

  • Largest WBCs, convert to macrophages in tissues, assist in phagocytosis.

Abnormal White Blood Cell Levels

• Leukocytosis: Abnormal increase in WBC count, often linked with infection:

  • If caused by neutrophils, termed neutrophilia.

• Leukopenia: Abnormal decrease in WBC count:

  • Neutropenia: Decrease specifically in neutrophils, can arise from chemotherapy or severe infections.

• Eosinophilia: Increased in allergic reactions and parasitic infections.

• Lymphocytosis: Increased lymphocytes seen in viral infections (e.g., mononucleosis).

• Lymphocytopenia: Decreased levels indicating immune deficiencies, significant in HIV.

• Monocytosis: Elevated in chronic infections like tuberculosis and autoimmune diseases.

Red Blood Cells (RBCs)

• RBC characteristics:

  • Life span of about 120 days, produced in bone marrow.

  • RBCs primarily composed of hemoglobin; critical for oxygen transport.

  • Do not migrate into tissues like WBCs; function centrally in the bloodstream.

Normal Red Blood Cell Values

• RBC Count:

  • Females: 4 - 5.4 x 10^12/L

  • Males: 4.6 - 6 x 10^12/L

• Hematocrit (HCT):

  • Females: 35% - 49%

  • Males: 40% - 54%

• Hemoglobin (Hgb):

  • Females: 12 - 15 g/dL

  • Males: 14 - 18 g/dL

Red Blood Cell Abnormalities

• Anemia: Decreased RBC count; can indicate underlying pathology.

• Polycythemia: Increased RBC production, can occur in response to chronic hypoxia or other stimuli.

Hemoglobin

• Function:

  • Major protein in RBCs, responsible for oxygen transport and maintaining acid-base balance.

• Each hemoglobin molecule contains four heme groups with iron ions that bind oxygen.

Platelets (Thrombocytes)

• Definition: Smallest blood cells, crucial for hemostasis; normal counts vary widely.

• Thrombocytopenia: Indicates low platelet counts, increasing bleeding risks.

Coagulation Testing

• Essential for assessing the coagulation pathway, includes:

  • Platelet Count

  • APTT (Activated Partial Thromboplastin Time): Measures intrinsic pathway of coagulation, normal range 25-35 seconds.

  • PT/INR (Prothrombin Time/International Normalized Ratio): Assesses extrinsic pathway, monitors anticoagulation therapy with medications like heparin and Coumadin.

  • D-Dimer: Measures fibrin degradation products, aids in detection of pulmonary embolism (PE).

Chemistry Laboratory Testing

• Basic Metabolic Panel includes:

  • Electrolytes, fasting glucose, and renal function tests such as BUN and creatinine.

Electrolytes

• Sodium (Na+): Normal values 135-145 mEq/L; regulates body fluids.

  • Hypernatremia: Loss of water.

  • Hyponatremia: Excessive water intake or sodium loss.

• Potassium (K+): Normal levels 3.5 - 5.0 mEq/L; crucial for cardiac and muscle function.

  • Hypokalemia: Low potassium indicated by decreased intake or increased loss, can lead to severe complications.

• Chloride (Cl−): Normal values 98-107 mEq/L; helps maintain fluid balance.

  • Hypochloremia: Associated with severe vomiting.

  • Hyperchloremia: Related to certain kidney disorders.

• Bicarbonate (HCO3): Key in acid-base balance; elevations indicate metabolic alkalosis; decreases are seen with acidosis.

• Calcium (Ca²+) & Magnesium (Mg²+): Important in muscle and nerve function; calcium also aids in bone health.

Glucose

• Function: Primary energy source; normal fasting range 70-99 mg/dL.

  • Hyperglycemia: Elevated levels indicating diabetes or other conditions.

Renal Function Tests

• BUN and Creatinine: Critical for assessing kidney function, but not overly sensitive to early disease indications.

  • Normal ranges:

  • BUN: 7-20 mg/dL

  • Creatinine: 0.7-1.3 mg/dL.

Hepatic (Liver) Panel

• Evaluates liver health via:

  • Proteins (Albumin and Globulin)

  • Liver enzymes: ALP, ALT, AST

  • Bilirubin: Byproduct of hemoglobin metabolism; elevated levels indicate liver dysfunction or hemolysis.

Lipid Panel

• Cholesterol Types:

  • HDLs (High-Density Lipoproteins): Good cholesterol, protective against heart disease.

  • LDLs (Low-Density Lipoproteins): Bad cholesterol, associated with arterial plaque.

• Triglycerides: Main form of fat storage; normal range 30 to 149 mg/dL.

Cardiac Biomarkers

• Role: Indicate myocardial injury or stress, including:

  • Creatine Kinase (CK)

  • Troponin: Elevated above 0.40 ng/ml indicates myocardial infarction (MI).

  • B-type Natriuretic Peptide (BNP): Level below 100 pg/ml suggests no heart failure.

Microbiology

• Areas:

  • Routine Bacteriology

  • Mycology

  • Parasitology

  • Virology

  • Mycobacteriology

Specimen Sampling Methods

• Preanalytical Phase: Involves specimen selection, collection, and transport.

• Sputum Collection:

  • Preferred for pneumonia diagnosis; should be clear and pale with minimal WBC.

• Bronchoalveolar Lavage (BAL): Useful for diagnosing interstitial lung disease; involves collecting lung fluid.

Histology and Cytology

• Biopsies assess lung tissue for malignancy.

• Cytology studies evaluate fluid and secretions for cancer presence.

Skin Testing for Diagnosis

• Tuberculin Skin Tests: Used for diagnosing infections, notably tuberculosis, and allergies.