blood bank exam 2

Rh antigens

reside on proteins and are very immunogenic

Rh antibodies

produced after exposure to foreign red blood cells

• are on carbohydrates

Rh frequency in whites

D: 85%

d- 15%

C- 70%

c- 80%

E- 30%

e- 98%

haplotype

the complement of genes inherited from either parent

How is the test performed-weak d

IAT

Is performed by taking the RBCs that tested negative in the immediate spin phase and incubating them at 37 C with anti-D reagent

• perform initial Rh typing by mixing patient cells with anti-D

• If negative, incubate and allow antibody uptake

• Wash the RBCs 3 times

• Add AHG

• centrifuge and examine for agglutination

Positive result = weak D positive

Why is the test performed- weak d

to detect a weak-d when a direct agglutination is not easily detected by immediate spin, ensuring accurate identification

How are weak D positive patients labeled

Rh-positive

How are weak D positive donors labeled

Rh-positive

What are three mechanisms by which you can be a weak D

Genetic (fewer D antigen sites)- change in structural gene

C trans on the D gene- proximity interferes with expression in D antigen

Partial D (mosaic)- one or more epitomes of the D protein

which of the weak Ds can actually make anti-D

Partial D individuals. because they are missing parts of the D antigen “mosaic” and can form an antibody against the parts they lack if exposed to whole blood

who gets Rh immune globulin (RhIg)

Rh-negative pregnant women who are carrying an Rh-Positive fetus, or Rh-negative individuals accidentally exposed to Rh-positive blood

what does Rh immune globulin do

It prevents alloimmunization against the D antigen by binding to and clearing fetal D-positive RBCs from the maternal circulation

• The IgG anti-D in the RhIG preparation attaches to the fetal RBCs in the mother's blood.

• The maternal spleen removes these coated cells before they can stimulate the maternal immune system to produce permanent anti-D antibodies.

What type of antibody is the Rh antibody?

It is an IgG antibody.

• Unlike ABO antibodies (which are primarily IgM), Rh antibodies are immune-mediated (IgG) and typically cross the placenta.

Where does the Rh antibody best react

It reacts best at 37°C (body temperature).

• Rh antibodies are "warm-reacting" antibodies, meaning they exhibit clinical significance at physiological temperatures.

Can Rh antibody cause hemolytic transfusion reaction or HDN

Yes, it can cause both

• Hemolytic Transfusion Reaction: Rh-positive blood given to a patient with anti-D leads to extravascular hemolysis

• HDN: Since Rh antibodies are IgG, they cross the placenta during pregnancy, attacking fetal D-positive RBCs and causing Hemolytic Disease of the Newborn

Does the Rh antibody bind complement

Generally, no

• Rh antibodies are primarily IgG1 and IgG3 subclasses, which do not efficiently fix or bind complement; hemolysis is typically extravascular via the reticuloendothelial system

How were the Rh antigens discovered

They were discovered in 1940 by Landsteiner and Wiener by injecting Rhesus monkey blood into rabbits and guinea pigs

how many antigens are there?

5: D, C, E, c, e

How are Rh antigens inherited

They are inherited as codominant alleles from each parent, organized as a haplotype

Which Rh antigen is the most immunogenic

the D antigen

Rh negative vs Rh positive

• Rh negative: Absence of the D antigen on the RBC surface.

• Rh positive: Presence of the D antigen on the RBC surface

If a patient has anti-C in their serum, what type of units should he/she receive for transfusion

The patient must receive C-negative blood units

What is the Rh null phenotype

A rare condition where an individual's RBCs lack all Rh antigens (D, C, c, E, e)

Do Rh null cells have Rh antigens

No, they lack the expression of all Rh antigens

What is the principle of the AHG test

The AHG test uses antihuman globulin to detect IgG antibodies or complement that have coated RBCs, which would not otherwise cause visible agglutination

What antibodies are found in polyspecific AHG

Anti-IgG and anti-C3d

What are check cells

Check cells are reagent RBCs that have already been coated with IgG (Coombs control cells)

How do you interpret the addition of check cells

If adding check cells results in agglutination, the AHG test is valid. If they do not agglutinate, the test is invalid

Why are RBCs washed in saline 3 times before adding AHG

To remove all unbound human globulins from the serum, which would otherwise neutralize the AHG reagent and cause a false-negative result

What does a positive DAT mean

It means that RBCs were coated with IgG or complement in vivo (inside the patient's body)

What does a positive IAT mean

It means that IgG antibodies in the patient's serum have successfully attached to reagent RBCs in vitro (in the laboratory testing environment)