Blood Bank Principles Review

Flashcards covering gel and microplate testing, intravascular and extravascular hemolysis, blood group genetics, parentage testing, antigen frequency calculations, and control selections based on the lecture transcript.

In gel matrix testing, what visual appearance distinguishes a negative (0) reaction from a 4+ positive reaction?

A negative (0) reaction forms a cell button at the very bottom of the gel tube, whereas a 4+ positive reaction forms a solid band of agglutinated red cells right on top of the gel matrix without penetrating it.

How is a mixed field reaction identified in gel testing?

A mixed field reaction displays a line of agglutinated red cells at the top of the gel matrix along with a cell pellet at the bottom of the tube.

How are positive and negative reactions interpreted in donor microplate testing?

A concentrated cell button in the middle of the microplate well indicates a positive reaction, while cells streaming from the middle down toward the side wall indicate a negative reaction.

At what specific point in the complement cascade does extravascular hemolysis stop?

Extravascular hemolysis stops at the $C3b$ step, where complement-coated red cells are cleared by macrophages instead of undergoing full membrane attack complex destruction.

What is Disseminated Intravascular Coagulation (DIC) and what is its main clinical consequence?

DIC is a condition involving small blood clots traveling throughout the circulatory system, which cause vessel blockages in vital organs and can lead to organ failure or death.

What are five key laboratory or clinical indicators of acute intravascular hemolysis?

A sudden drop in blood pressure (mediated by $C3a$ and $C5a$ anaphylatoxins), hemoglobinuria, hemoglobinemia (pink to red plasma), exhausted/depleted haptoglobin levels, and non-rising hemoglobin/hematocrit levels.

Which blood group antigen pairs are classified as antithetical?

Antithetical pairs include Big C and little c, Big E and little e, Duffy a ($Fy^a$) and Duffy b ($Fy^b$), M and N, Big S and little s, and $Jk^a$ and $Jk^b$.

Which antigens mentioned in the lecture lack an antithetical partner?

The P1 antigen and the D antigen (there is no little d antigen).

What is the dosage effect in blood group serology, and which Rh antigen does not show dosage?

Dosage occurs when an antibody reacts more strongly with red cells homozygous for an antigen than with cells that are heterozygous. The D antigen does not show dosage because it has no antithetical partner.

What characterizes the Rh null phenotype, and what type of blood must these patients receive?

Rh null individuals lack all Rh system antigens (no D, C, c, E, or e) and must be transfused exclusively with Rh null blood.

What is the difference between cis and trans positions in genetics, and how does C in trans position affect D antigen reactivity?

Cis position means genes are inherited on the same chromosome, while trans position means they are inherited on opposite chromosomes. Inheriting the Big C gene in trans to the D gene causes weaker expression and reactivity of the D antigen due to competition.

What defines a direct exclusion in relationship testing?

A direct exclusion occurs when a child possesses a gene or antigen that is completely absent in both the mother and the alleged father (e.g., a group O mother and group B father having a group A child).

What defines an indirect exclusion in relationship testing?

An indirect exclusion occurs when a child lacks a genetic marker that an alleged father, who is homozygous for that marker, must have passed on.

What is an obligatory gene in paternity testing?

An obligatory gene is the specific gene that must have been contributed by the biological father to the offspring.

How is the number of donor units to screen calculated when a patient requires antigen-negative blood?

Subtract each antigen's percent positive frequency from 100% to get the negative frequency, convert to decimals and multiply them together to get the combined probability, then divide the required number of units by this probability.

When selecting positive controls for antigen testing, why is a heterozygous cell chosen instead of a homozygous cell?

A heterozygous cell is selected for a positive control because it expresses a lower antigen density, providing the weakest possible positive reaction to verify the test's analytical sensitivity.

What is the requirement when selecting a cell for a negative control in blood group antigen testing?

The negative control cell must completely lack the specific antigen that is being tested for.