ClinicalDiagnostic Testing Theory

Hematology

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

Why Perform Diagnostic Testing?

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

Definitions

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

Facilities

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

Facilities

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

Physicians◦ Many physicians have chosen to specialize in

laboratory fields Hematologist Pathologist Cytologist Radiologist etc

Professionals con’t

DefinitionThe 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

Hematology

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 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 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 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 Tests

◦Red Blood Cell Morphology Shape, size and colour of 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 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

◦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’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

Commonly Ordered Tests con’t

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 Bank / Blood Transfusion

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 Typing

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

Blood Type Testing

Many physicians send patients directly to the lab to have blood work 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

Preparing and Handling Blood Specimens

◦ Before lab courier arrives, double check requisition forms against vials and place in cooler bag

◦ Blood specimens for serum testing have to be centrifuged before being sent– these should not be placed in the fridge until the process is complete

All specimens, whether blood or other body substances, must be transported in accordance with the Transportation of Dangerous Goods Act

Preparing and Handling Blood Specimens

Lab Requisition

Deals with tests on urine, blood plasma, and other body fluids

Chemistry

Serum samples are obtained by centrifuging clotted blood samples to separate the solid components

Tests on Serum

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

Commonly Ordered Serum Tests

Creatinine◦ Byproduct 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 Tests

Electrolytes (Lytes)◦ Elements found in body tissues and blood

Ex sodium, potassium, chloride Reference Ranges:

Sodium 135-145 mEq/L Potassium 3.5-5.0 mEq/L Chloride 99-108 mEq/L

Commonly Ordered Serum Tests

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 Glucose Testing

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 Glucose Testing

Random Blood Sugar (RBS) May be taken anytime Only indicates unusual activity Reference Range

Adult 3.6-7.8 μmol/L

Glycosylated Hemoglobin (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%

Blood Glucose Testing

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

Other Common Serum Tests

◦Triglycerides Elevated levels are associated with heart

disease, arteriosclerosis, atherosclerosis Reference Range:

<1.7 μmol/L

Other Common Serum Tests

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/Lfemale 26-140 μmol/L

Other Common Serum Tests