Diagnostics, Serology, PCR, and Blood Group Antigens

Flashcards covering diagnostics, serology principles, PCR advantages, canine and feline blood group systems (DEA and AB systems), transfusion medicine, crossmatching, and neonatal isoerythrolysis.

What is serology (immunologic testing)?

Diagnostic testing that utilizes antibodies and enzymes to detect antigens or antibodies in serum or plasma, commonly used for endocrinology, infectious agent detection, drug monitoring, and allergy testing.

How is diagnostic sensitivity defined and calculated?

A measure of a test's ability to correctly identify all positive animals as positive, calculated as: $\text{sensitivity} = \frac{\text{true positives}}{\text{true positives} + \text{false negatives}}$

How is diagnostic specificity defined and calculated?

A measure of a test's ability to correctly test negative when the patient is truly negative, calculated as: $\text{specificity} = \frac{\text{true negatives}}{\text{true negatives} + \text{false positives}}$

What inverse relationship exists between diagnostic sensitivity and specificity?

As one metric is maximized, the other is decreased; for instance, a test with $100\%$ sensitivity is prone to generating an increased number of false-positive results.

In clinical pathology, what is the definition of an assay?

An analysis of a specific substance (analyte) to determine something about its quantity, quality, or function.

How does an enzyme-linked immunosorbent assay (ELISA) function?

It pairs an enzyme-attached antibody or antigen with the patient sample; binding triggers an enzymatic reaction that yields a colored product (such as a blue dot) corresponding to the presence and concentration of the target analyte.

What are the two primary diagnostic capabilities of polymerase chain reaction (PCR)?

1. Detecting a specific DNA target sequence (if present) in diverse sample types, including minute samples.
2. Amplifying or cloning that detected sequence into thousands or millions of copies for further diagnostic testing.

Why is PCR able to confirm a negative infection status sooner than serology following pathogen clearance?

PCR directly detects pathogen DNA, which clears quickly once eliminated, whereas serology detects antibodies that can persist in circulation for days, weeks, months, or years.

What are blood group antigens?

Structures (antigens) present on the surface of an individual animal's red blood cells that may react with plasma antibodies from another individual of the same or different species.

What are alloantibodies, and which species lack them naturally?

Naturally occurring antibodies that an animal possesses against different red blood cell antigens of its own species. They occur in cats, cattle, sheep, and pigs, whereas dogs do not have pre-existing alloantibodies.

How do kittens obtain alloantibodies if they are not ingested through colostrum?

Kittens will naturally begin synthesizing their own alloantibodies at $6\text{ to }8\text{ weeks}$ of age.

What is the most common indication for administering a blood transfusion in veterinary medicine?

Severe anemia resulting from underlying medical conditions or hemorrhage.

What is the red blood cell concentration in packed red blood cells (packed RBCs)?

$70\text{--}80\%$ red blood cells, combined with an anticoagulant.

What is the primary diagnostic purpose of a crossmatching test?

To visually confirm compatibility by predicting whether abnormal agglutination or hemolysis will occur when donor and recipient blood are mixed; it does not identify the patient's blood group antigen type.

In canine blood typing, what does the acronym DEA stand for and what does a decimal number represent?

Dog Erythrocyte Antigen; the number in the tenths place (such as DEA 1.1) designates a subtype within that antigen group.

Why is DEA 1.1 the most clinically significant blood group antigen in dogs?

Reactions against DEA 1.1 are the only canine blood group reactions considered clinically significant and life-threatening; reactions against other DEA types are generally mild or non-life-threatening.

Why are DEA 1.1 positive dogs considered universal recipients?

They do not synthesize antibodies against DEA 1.1 because they already possess the antigen, and exposure to other DEA types does not produce clinically significant transfusion reactions.

Which canine blood type is designated as the universal donor for both initial and repeated transfusions?

DEA 1.1 negative.

What percentage of Greyhounds test negative for DEA 1.1?

Approximately $60\%$ of Greyhounds.

What infectious diseases should canine blood donors be screened for?

Heartworm disease, brucellosis, ehrlichiosis, anaplasmosis, and neorickettsiosis, alongside other regionally prevalent pathogens.

How can a prior transfusion in a breeding bitch lead to neonatal isoerythrolysis in her puppies?

If a DEA 1.1 negative bitch receives DEA 1.1 positive blood, she forms anti-DEA 1.1 antibodies that pass into colostrum; if bred to a DEA 1.1 positive sire, DEA 1.1 positive puppies ingest these antibodies, leading to red blood cell destruction.

What three blood types comprise the feline AB blood group system?

Type A, Type B, and Type AB (where AB is an independent antigen rather than a codominant expression of A and B).

What proportion of cats in the United States are Type A, and what titer of alloantibodies do they carry?

Approximately $90\%$ of cats are Type A, and they possess weak (low titer) naturally occurring alloantibodies against Type B red blood cells.

Why does a Type B cat suffer a life-threatening reaction upon its very first transfusion of Type A blood?

Type B cats possess high-titer, naturally occurring anti-A alloantibodies that immediately trigger massive hemolysis and agglutination upon exposure to Type A red blood cells.

Why is there no universal blood donor among cats?

Because Type A and Type B cats naturally possess pre-existing alloantibodies directed against the opposite blood group antigens.

What is the difference between a major crossmatch and a minor crossmatch?

A major crossmatch evaluates recipient plasma for antibodies against donor red blood cells, whereas a minor crossmatch evaluates donor plasma for antibodies against recipient red blood cells.

How is neonatal isoerythrolysis in kittens prevented when high-risk matings occur?

By blood typing breeding queens and toms beforehand, and separating newborn kittens from high-risk mothers during their first $24\text{ hours}$ of life to prevent colostral antibody absorption.