Serology and Immunohematology

1
Chapter 46

• Serology and Immunohematology

2
Introduction

• Serology is the study of antigens and antibodies
• Immunohematology refers to testing done in blood
  banks on red blood cells
• All testing requires the use of Standard
  Precautions

3
Antigens and Antibodies

• Antigens are substances recognized as foreign by
  the body
• Antibodies are proteins produced by the body in
  response to specific antigens

4
Checkpoint Question 1

• How would you describe a test that is both
  specific and sensitive?

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Answer

• A test that is specific and sensitive can measure
  a substance even if only a tiny amount is present
  (specificity), and it can pick that substance out
  of a solution containing millions of other
  related substances (sensitivity).

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Serology Test Methods and Principles

• Agglutination of visible particles
• Enzyme linked immunosorbent assays (ELISA)
• Other methods
• Agglutination inhibition
• Competitive binding assays

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Agglutination Test

• Mix together reagent and sample on paper card or
  glass plate
• Gently rock reagent and sample back and forth
• Observe for agglutination

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Agglutination Test (continued)

• If specific antigen is in reagent, then serum can
  be tested for the specific antibody
• Infectious mononucleosis
• Rheumatoid arthritis
• Syphilis
• Rubella.
• If reagent has antibody attached, then specimen
  can be tested for specific antigen
• Streptococci

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Enzyme Linked Immunosorbent Assays

• ELISA tests come with necessary reagents packaged
  in a kit
• Be sure to follow manufacturers instructions
• Results are easy-to-read color change

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Checkpoint Question 2

• What are two serology test methods, and how do
  they indicate the presence of the test substance?

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Answer

• Two serology test methods are agglutination,
  enzyme linked immunosorbent assay. Enzyme
  immunoassays produce a color change. With
  agglutination tests, clumping of particles
  (agglutination) occurs if the test substance is
  present.

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Reagent and Kit Storage and Handling

• Kits must be stored at temperature recommended on
  box
• Room temperature
• Refrigerator
• Reagents should never be used past expiration
  date
• Follow specific specimen collection guidelines
  for each kit

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Checkpoint Question 3

• Why is it important to store reagent kits at
  specified temperatures?

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Answer

• Improperly stored kits may result in
  deterioration of the reagents, which may lead to
  false test results.

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Following Test Procedures

• Test principle and clinical use of test
• Reagents and materials needed to do test
• Precautions
• Specimen collection and handling
• Controls to be run and how often

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Following Test Procedures (continued)

• Step-by-step procedure to follow
• Interpretation and reporting of results
• Normal or expected values
• Test limitations

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Quality Assurance and Quality Control

• Kits should be tested periodically for continued
  stability of all reagents
• Quality control (QC) test needs to be performed
  each time the reagents are used

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External Controls

• Solution similar to a patient sample is tested a
  patient sample
• Its value or expected result is already known
• If controls do not give the expected result,
  patient results should not be reported

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Internal Controls

• Technique controls are built into the test packs
• Monitor that test procedure is followed correctly
  and reagents are working properly
• Do not report patient results if controls do not
  give proper reactions

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Serology Tests

• Many serological tests exist
• Some common tests are performed in medical office

21
Rheumatoid Factor/Rheumatoid Arthritis

• Autoimmune progressive inflammatory disease of
  the joints
• Test for agglutination
• False-negative result
• Negative result when patient does have disease
• False-positive result
• Positive result when patient does not have disease

22
Checkpoint Question 4

• What is the difference between a false-negative
  and a false-positive test result, and why do
  these sometimes occur?

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Answer

• A false-negative result occurs when a patient
  tests negative for a disease, even though the
  disease is present. A false-positive result
  occurs when a test indicates that a patient has a
  particular disease, even though the patient is
  disease free. These results can be caused by
  technical problems in performing the test or by
  the patients biologic condition.

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Infectious Mononucleosis

• Caused by Epstein-Barr virus
• Testing
• Agglutination of RBCs or latex particles
• ELISAs
• Results
• False-negative early in the disease
• False-positive results by waiting too long to
  read agglutination tests

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Rapid Plasma Reagin Test for Syphilis

• Sexually transmitted disease caused by Treponema
  pallidum
• RPR is agglutination test
• Physician and health department must be notified
  of reactive results for syphilis

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Pregnancy Test

• Based on detection of human chorionic
  gonadotropin (HCG)
• Testing
• Agglutination
• ELISA
• Urine or serum is added to test pack
• Internal positive and negative control areas must
  react appropriately for valid results

27
Group A Streptococcus

• One of most common bacterial causes of sore
  throat and upper respiratory tract infections
• Testing
• Bacterial culture
• Agglutination
• ELISA

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Checkpoint Question 5

• What are the benefits and drawbacks of using
  serology tests versus cultures for group A
  streptococcus?

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Answer

• Serology tests are easier to perform and provide
  results more quickly, but cultures are considered
  to be more sensitive.

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Immunohematology

• Determines if donor blood is compatible for
  transfusion
• If compatible, RBCs circulate in recipients body
  for longer time
• If incompatible, recipients body will begin
  destroying donor blood
• Rapidly leads to death

31
Blood Group Antigens

• Transfusion compatibility determined by testing
  antigens present on donor and recipient RBCs and
  antibodies present in recipients serum
• ABO group
• Rh type
• Other blood groups

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ABO Group

• Four blood groups A, B, O, or AB
• Almost all serum contains antibodies to ABO
  antigens it lacks
• Antibodies are crucial to safe transfusion

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Rh Type

• Rh group includes antigens D, E, C, e, c
• Presence of D antigen is Rh positive
• Absence is Rh negative
• Antibodies to D do not occur naturally

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Rh Type (continued)

• Those lacking D antigen must be exposed to D
  antigen of foreign RBCs to produce antibodies
• Rh-negative patient is transfused with
  Rh-positive blood
• Rh-negative mother is exposed to Rh-positive
  cells of her baby before or during childbirth

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Other Blood Groups

• Other RBC antigens
• Duffy, Lewis, MNS, Kidd, Kell
• White blood cells and platelets also have
  antigens
• Human leukocyte antigens

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Blood Group Testing

• ABO Testing
• Direct or forward typing
• Indirect or reverse typing
• Rh Testing
• Anti-D reagent is used to determine the Rh of
  RBCs

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Checkpoint Question 6

• Which ABO blood group is the universal donor?
  What does this mean?

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Answer

• Type O is the universal donor because it lacks A
  or B antigens, making it safe to give patientsno
  matter what their ABO group.

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Blood Supply

• American Red Cross and other agencies collect
  donor blood
• Shortage of donor blood
• Donor blood divided into three products
• 1. Packed RBCs
• 2. Plasma
• 3. Platelet concentrates

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Checkpoint Question 7

• What are three products that can be obtained from
  1 U whole blood and how are they used?

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Answer

• A single unit of whole blood can be divided into
  packed RBCs (used to treat anemia) plasma (used
  to treat bleeding from a lack of coagulation
  factors) and platelet concentrates (used to
  treat bleeding caused by low platelet count or
  dysfunctional platelets).