Unit 1 - Intro

CLINICAL PATHOLOGY

VTEC 1140

Unit #1: Introduction to Clinical Pathology

WHO AM I?

  • Lilac breasted Roller
    • Courtesy of Dr. Paula Davies

BLOOD

  • Purpose of Blood Collection:
    • Often collected to determine what is going on internally with a patient.

COMMON TESTS PERFORMED ON PATIENTS

  • Types of Tests:

    • Complete Blood Count (CBC)
    • Chemistry tests
    • Urinalysis
    • Fecal floats
    • Enzyme-linked immunosorbent assays (ELISA)
    • Polymerase Chain Reaction (PCR) tests
    • Spec cPL (canine), fPL (feline)
    • And many others…

  • Sources of Results:

    • Some of these tests can be run on blood, others can be done in-clinic, some need to be sent out to an external lab.
    • Photo courtesy of Dr. Aley 2021.

  • Testing Methodologies:

    • Using antigen/antibody to assess if the pathogen is present in the specimen.
    • Looking at DNA for analysis.

TESTING ENVIRONMENT

  • Larger Centers or Veterinary Schools:
    • Many tests available with potential delays in results (depending on geography).
    • Results generally reported by pathologists.
    • Example: IDEXX lab in Delta, B.C.

VARIABLE INFLUENCES ON TEST RESULTS

  • Overall Influence:
    • Every test performed is influenced by numerous patient and environmental variables, which may influence the accuracy/value of the results generated.

Pre-Analytic Variables

  • Definition: Variables occurring from the moment the test is ordered until the test is run.
  • Sources of Influence:
    • Patient Variables:
    1. Non-controllable:
      • Signalment: species, age, breed, sex, etc.
    2. Controllable:
      • Fasted/not fasted
      • Diet
      • Exercise
      • Medications (Drugs)
      • Can influence the range of values (e.g., different breeds, sexes, ages).
      • Clinical Effects:
      • Sugar and fats can alter blood results.
      • Stress, cortisol, and TPR (temperature, pulse, respiration) can impact readings.

SAMPLE VARIABLITY

  • Sample Handling:

    1. Collection:
    • Success of venipuncture (e.g., hemolysis influencing measurements).
    • Type of tube used (correct color/type and use of proper anticoagulant: EDTA vs. citrate vs. heparin).
    1. Handling/Storage/Transportation:
    • Labeling accuracy (legible animal info, specimen type, date, time).
    • Separation of elements:
      • Plasma: separate immediately.
      • Serum: allow to clot first.
    • Temperature considerations for storage or shipping (does it require ice?).
    • Artifacts:
      • Storage artifacts such as hypoglycemia, hyperkalemia, hemolysis due to improper handling.

  • Clinical Considerations:

    • Plasma transfusions for patients with low blood pressure needing clotting factors and blood proteins.

ANALYTIC VARIABLES

  • Phase Definition: Occur while the test is being performed.
  • Determining Factors:
    • Characteristics: A) Analyzer characteristics (machine or test). B) Sample characteristics (e.g., hemolysis, lipemia).
      • Example: The clarity of serum affecting refraction readings may skew counts.

POST-ANALYTICAL VARIABLES

  • Definition: Variables affecting results post-analysis.
  • Importance:
    • Accurate recording, handling & interpretation are crucial.
    • Urine samples must be processed timely for valid culture results.

RECORDING RESULTS

Qualitative Results

  • Evaluation of presence or absence.
    • Answers Yes or No.
    • Example: Snap test for a parasite.

Quantitative Results

  • Actual measurement of analyte present expressed in units/volume.
    • Semi-quantitative measures may be represented as +, ++, +++.
    • Example: Ear cytology reporting 2+ yeast on a slide.

REFERENCE RANGE

  • Definition: A range of values based on results from a population of healthy animals.
    • Represented in a “bell” curve, including only 95% of the healthy population.
    • High and low 2.5% values are not included (indicates potential outliers).
    • Importance of Individual Comparison: Always compare an individual’s sample to previous samples.
    • An individual may be healthy but still outside the reference range due to sample variance.
    • Example: Compare sick vs. healthy results of the same patient.
    • Blood tests represent a moment in time; trends are vital for accuracy (e.g., diabetic cats, liver values).

TEST INTERPRETATION

  • Critical Thinking:
    • The quality of a test depends on the analyst's interpretation.
    • Aspects for Consideration:
    • Verify the correctness of test execution.
    • Analyze whether results align with expectations.
    • Understand reference ranges are specific to individual laboratories.
    • Ensure that understanding sample handling instructions tailored to the laboratory/test type.
    • Reflect on the appropriateness of chosen tests.

IMPORTANCE OF BLOOD

What makes blood precious?

  • Functions of Blood:
    • Supports the immune system.
    • Maintains pH balance.
    • Contains proteins, enzymes, electrolytes, minerals, and hormones.
    • Fights infections and carries oxygen.

COURSE OUTLINE

HEMATOLOGY

  • Study of blood and hemostasis (ability to clot).
  • Focus on Complete Blood Count (CBC).
    • Evaluates cellular components:
    1. Red Blood Cells (RBCs)
    2. White Blood Cells (WBCs)
    3. Thrombocytes (platelets)

BIOCHEMISTRY OF BLOOD

  • Evaluation of blood biochemistry to identify:
    1. Organ abnormalities (e.g., kidneys, liver).
    2. Electrolyte balance and pH changes (e.g., Sodium, Potassium).
    3. Blood mineral levels (e.g., Calcium, phosphorus).
    4. Effects of medications and treatments.
    5. Yearly changes in blood profiles.
    6. Blood sugar levels (glucose).
    7. Hormonal levels (e.g., thyroid T4).
    8. Stress levels (cortisol).

COMPLETE BLOOD COUNT (CBC)

Definition

  • Blood test evaluating three major cell types:
    1. Red Blood Cells (Erythrocytes): Transport oxygen.
    2. White Blood Cells (Leukocytes): Immune status.
    3. Platelets (Thrombocytes): Clotting ability.

Information Derived from CBC

  • Describing the efficient transport of oxygen, immune status, and bleeding mechanisms from platelets.

BIOCHEMISTRY SCREEN

Purpose

  • Evaluates organs and systems in health.

CBC Portion of Bloodwork Example

  • Assessment indicators:
    • Erythrocytes values reported with reference ranges, e.g.,
    • RBCs: 2.8 (normal 5.5 - 8.5).
    • WBC: 14.7 (normal 6.0 – 17.1).

COMMON CLINICAL FINDINGS

Anemia Indicators in Blood Results

  • Examples:
    • Evidence of regenerative anemia characterized by reticulocytosis and possible internal destruction or consumption signs (e.g., spherocytes).

Diagnosis Process

  • A single test provides significant clues.
    • A diagnosis of Immune-Mediated Hemolytic Anemia (IMHA) can involve the immune system attacking red blood cells directly, resulting in anemia.

BLOOD COMPONENTS

Composition Overview

  • Plasma: Liquid component separating cells post-centrifugation. Contains proteins and various nutrients.
  • Cellular Elements:
    • Erythrocytes (RBCs)
    • Leukocytes (WBCs)
    • Thrombocytes (Plates
    • Buffy Coat: Contains most WBCs and platelets when spun down in purple top samples.

LAW OF BLOOD SEPARATION

Tube Protocols

  • Lavender Top Tube:
    • Centrifuged to create layers: Plasma, Buffy coat, RBCs.

Clinical Relevance of Blood Types

  • Differences between plasma and serum:
    • Plasma (EDTA): Contains fibrinogen, cannot be used for certain tests (e.g., chemistry analyses).
    • Serum (Red Top Tube): Can be spun down post-clotting, free from clotting factors, allowing for chemistry analysis.

END OF NOTES

  • Any questions?
    • Courtesy of Paula Davies, August 2022.