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Clinical. Diagnostic Testing Theory Hematology. Why Perform Diagnostic Testing?. Valuable source of information for medical diagnosis Visualize and analyze body structures, tissues, and fluid Tool for disease screening Early detection of conditions for prompt treatment

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Diagnostic Testing Theory


why perform diagnostic testing
Why Perform Diagnostic Testing?
  • Valuable source of information for medical diagnosis
    • Visualize and analyze body structures, tissues, and fluid
  • Tool for disease screening
  • Early detection of conditions for prompt treatment
  • Baseline information for patients undergoing treatment or surgery
  • Homeostasis:

the normal state of balance or equilibrium in the human body

  • Reference Range:

Range of values normally expected for a particular test

  • Abnormal:

Results that are above or below the reference range

  • Test Profiles:

Tests that are commonly ordered in groups

  • Private Labs
    • Freestanding or located within clinics
    • Provide analysis of blood and other tissues, x-ray, ultrasonography, mammography, etc
      • May also have satellite specimen collection labs
  • Public Health Labs
    • Operated by the government
    • Provide analysis of specimens for diseases of public concern
      • ie HIV, Hepatitis, SARS, West Nile
  • Hospitals
    • Most hospitals have facilities for:
      • Hematology
      • Immunohematology
      • Chemistry
      • Microbiology
      • Histology/Pathology/Cytology
      • X-ray
    • May also have other diagnostic testing facilities:
      • CT Scan, MRI, Ultrasound, etc
  • Allied Health
    • Medical Laboratory Technologist
      • Can supervise and carry out all clinical laboratory testing
      • 3 yr college and/or university program
    • Medical Laboratory Technician
      • Can perform clinical testing under supervision
      • 1 year course
    • Phlebotomist
      • Can collect hematological specimens (draw blood), prepare and maintain equipment, clerical tasks
      • Usually performed by the lab technologist or other specially certified health professional
professionals con t
Professionals con’t
  • Physicians
    • Many physicians have chosen to specialize in laboratory fields
      • Hematologist
      • Pathologist
      • Cytologist
      • Radiologist
      • etc
  • Definition

The study of blood; processing and evaluation of blood and blood components

  • Review of blood physiology
    • Human body contains 4-5 L of blood
    • Blood is composed of plasma, red blood cells, white blood cells, and various proteins, hormones, antibodies, etc
  • Hematological testing is mostly concerned with the cellular components of blood
commonly ordered tests
Commonly Ordered Tests
  • Complete Blood Count (CBC)
    • One of the most commonly ordered tests
    • Provides basic information about blood and blood forming tissues
    • Typically can include:
      • Red Blood Cell Count (RBC)
      • Hematocrit
      • Hemoglobin
      • White Blood Cell Count (WBC)
      • Differential Blood Count (diff)
      • Platelet Count
commonly ordered tests1
Commonly Ordered Tests
  • Red Blood Cell Count
    • Counts the number of erythrocytes in a specific volume of blood
    • Can help with a diagnosis of anemia, etc
    • May also evaluate size (MCV), weight (RDW), and hemoglobin concentration (MCH) of RBCs
    • Reference Range
      • Male: 4.7-6.1x1012 /L
      • Female: 4.2-5.4x1012 /L
commonly ordered tests2
Commonly Ordered Tests
  • Hemoglobin (Hb or Hgb)
    • The amount of hemoglobin found in a specific volume of blood
    • Often used to diagnose anemia or hemorrhage
    • Varies with altitude, gender, age
    • Reference Range
      • Male: 138 -172 g/L
      • Female: 121 -151 g/L
commonly ordered tests3
Commonly Ordered Tests
  • Hematocrit (Hct)
    • Percentage of total blood volume occupied by packed red blood cells (RBC)
    • Abnormal result may result from diminished production of RBC’s, blood loss, abnormal destruction of cells
    • Pregnant women normally have a low hematocrit
    • Reference Range
      • Male: 0.40 – 0.50/L or 40-50%
      • Female: 0.36 – 0.44/L or 36-44%
commonly ordered tests4
Commonly Ordered Tests
  • Red Blood Cell Morphology
    • Shape, size and colourof cells can be used to diagnose certain conditions
      • Ex Sickle cell anemia, Vitamin B12 or folate deficiency
  • Platelet Count
    • Actual count of the number of platelets in the blood
    • Low count may indicate bleeding disorder
commonly ordered tests5
Commonly Ordered Tests
  • White Blood Cell Count (WBC)
    • Determines the total number of white cells in the sample
    • May be divided into the five main types (Differential Count or diff)
      • Neutrophils, lymphocytes, monocytes, eosinophils, and basophils
      • An abnormal count of one or two types of white cells may indicate a certain type of condition
    • Reference Range:
      • 4.0 x 109 – 11.0 x 109/L for adults
commonly ordered tests con t
Commonly Ordered Tests con’t
  • Erythrocyte Sedimentation Rate (ESR or sed rate)
    • Measure how fast RBC’s settle over a specific period of time (usually 1 hour)
    • Not specific – can indicate presence of infection, inflammation, cancer, kidney disease, rheumatoid arthritis, etc
commonly ordered tests con t1
Commonly Ordered Tests con’t
  • Coagulation Studies
    • Used to measure the clotting time of blood
    • Useful for evaluating patients on blood thinners or anticoagulants
      • Prothrombin Time / International Normalized Ratio (PT/INR) and Partial Thromboplastin Time (PTT)
        • Assess the action of specific clotting factors in the blood
        • Can be used to diagnose bleeding conditions
        • Used for patients on heparin or Coumadin to make sure dosage is in the therapeutic range
        • Reference Range:

INR 0.9-1.2 (2.0-3.0 if on warfarin therapy)

- Other ranges apply for different medications

blood bank blood transfusion
Blood Bank / Blood Transfusion
  • Supplies screened and maintained by Canadian Blood Services
    • Also maintains Canadian Bone Marrow Donor Registry
  • Hospital Immunohematology department must ensure that blood products given to a patient are compatible with the patient’s blood (Cross-typing)
    • Transfusion of mismatched blood may cause serious, even fatal reaction
blood typing
Blood Typing
  • Four main blood types:
    • A, B, AB, O
      • The letters refer to antigens that sit on the surface of the RBC’s
    • Each blood type carries antibodies to the other antigens
  • Another antigen is the Rhesus or Rh factor
    • If you have the antigen you are Rh positive, if not you are Rh negative
blood type testing
Blood Type Testing
  • Cross-matching is done for patients that may require transfusion
    • Example – if a patient has a low Hgb/Hct due to a bleed
    • Also done for patients entering surgery
    • In emergencies, no time may exist for cross-matching and O negative blood may be ordered
  • Coombs test – indirect
    • Measures antibodies other than ABO or Rh that may cause problems with matching
preparing and handling blood specimens
Preparing and Handling Blood Specimens
  • Many physicians send patients directly to the lab to have bloodwork done. If the doctor takes their own specimens:
    • Physician will place all specimens in appropriate vials and label them
    • Print out requisition (or obtain requisition from physician) and make sure all information is filled in
    • Place vials in refrigerator until ready to prepare shipment
    • Before lab courier arrives, double check requisition forms against vials and place in cooler bag
    • Some blood specimens have to be centrifuged before being sent (serum tests) – these should not be placed in the fridge until the process is complete
  • Deals with tests on urine, blood plasma, and other body fluids
tests on serum
Tests on Serum
  • Serum samples are obtained by centrifuging clotted blood samples to separate the solid components
commonly ordered serum tests
Commonly Ordered Serum Tests
  • Blood Urea Nitrogen (Urea or BUN)
    • Measures the amount of urea in the blood
      • Urea is a by-product of metabolism and is cleared from the blood by the kidney
      • Build-up of urea can indicate compromised kidney function
      • Reference Range: 3.5 – 7 μmol/L
  • Creatinine
    • By-product of creatine phosphate – a compound in skeletal muscle tissue that is produced continually and cleared by the kidney
      • Extra creatinine in the serum can indicate renal dysfunction, certain muscle diseases, congestive heart failure
      • Reference Ranges:
        • Male: 62-120 μmol/L
        • Female: 55-115 μmol/L
commonly ordered serum tests1
Commonly Ordered Serum Tests
  • Electrolytes
    • Elements found in body tissues and blood
      • Ex sodium, potassium, chloride
      • Reference Ranges:
        • Sodium 135-145 μmol/L
        • Potassium 3.5-5.0 μmol/L
        • Chloride 99-108 μmol/L

Blood Glucose (Sugar)

    • Diagnose and monitor various metabolic diseases including diabetes mellitus
    • Various versions of the tests differing in what patient has to eat or drink and the time of day
      • Fasting Blood Sugar (FBS)
        • Client must remain NPO for at least 8 hours before the test
        • Reference ranges
          • Adult 3.3-5.8 μmol/L
          • Child 3.3-5.5 μmol/L
          • Less than 2 is considered a critical low
          • More than 20 is considered a critical high

Blood Sugar con’t

      • A screening test for glucose is usually completed by taking a FBS followed by a 2 hour Postprandial test and/or a Glucose Tolerance Test
      • Two-hour Postprandial Glucose level (2 hr PC BS or 2 hr PPG)
        • Taken two hours after eating
        • Reference Range:
          • Adult 3.3-7.8 μmol/L
      • Glucose Tolerance Test (GTT)
        • Patient is given a standard dose of glucose
        • Sample for testing is taken after set interval (usually 2 – 3 hours)

Blood Sugar con’t

      • Random Blood Sugar (RBS)
        • May be taken anytime
        • Only indicates unusual activity
        • Reference Range
          • Adult 3.6-7.8 μmol/L
      • GlycosylatedHemoglobin (HbA1c, GHb, glycohemoglobin)
        • Used to measure the effectiveness of diabetes treatment
        • Can indicate how much glucose was in a patient’s blood in the last 2 to 4 months
        • Reference Range
          • 4-6%

Cholesterol / Triglycerides

    • Measure the different types of fats in the blood
    • Patient usually must fast for 12 hours before the test
      • Cholesterol measured as LDL (bad) and HDL (good)
      • Reference Ranges
        • HDL male: 1.0-1.8 μmol/L

female: 1.2-2.4 μmol/L

- LDL adult 1.4-4.0 μmol/L


Cholesterol / Triglycerides con’t

    • Triglycerides
      • Elevated levels are associated with heart disease, arteriosclerosis, atherosclerosis
      • Reference Range:
        • <1.7 μmol/L

Heart (Cardiac) Enzymes

    • Enzymes are released into the bloodstream when heart muscle is damaged (MI)
    • Measuring the enzymes can inform if heart attack has occurred and how extensive the damage is
    • Often better at indicating MI than ECG
    • Usually measure creatine phosphokinase (CK) and troponin
    • Reference Range
      • CK male 39-174 μmol/L

female 26-140 μmol/L