11.6: Transfusion I Flashcards
What does immune mediated mean?
- Antibody and antigen mediated
- Not cellularly mediated
What is the AHG test?
“Anti-human globulin” test
- AKA the Coomb’s test
- Required for compatibility testing in blood bank
- Performed in vitro
What do all hemolytic problems with transfusions have in common?
- Antigen antibody mediated
- Immunoglobulin and or complement binding mediating RBC destruction
- In vivo destruction of RBC
What is positive coomb’s test associated with?
- An immune hemolytic state
- This is an abnormal state
Life of RBC?
- 120 days
- Only last minute or hours in immune mediated hemolytic state
What are the 3 antibodies associated with hemolysis?
- ISOagglutinins
- ALLOantibodies: made against own species but w/ different genetics
- AUTOantibodies
What are ISOagglutinins?
- Naturally occurring against gut bacteria that share polysaccharide epitopes
- Often IgM
- Activate complement
- Cause intravascular hemolysis
What do ISOagglutinins cause?
INTRAvascular hemolysis
Two main antigens on RBCs?
- A antigen: N acetyl galactosamine
- B antigen: Galactose
Types of ISOagglutinins in plasma based on blood type?
A: Anti B
B: Anti A
AB: None
O: Anti A, Anti B, anti AB
Which is the universal donor?
O, no antigens on them
Which is universal recipient?
AB, no isoagglutinins
What are blood transfusions unavoidably unsafe?
- A transplant of living, human tissue
Two most important factors in administering blood transfusion?
WILL BE ON EXAM
- Specimen identification
- Patient identification
* **Avoid transfusion if possible
What is the antibody screening test?
- Looking for alloantibodies
- Antibodies that are not anti A/B but are against the donor cell
- Use screening cells that present most of the significant, non-ABO antigens found on RBCs
- Normally is negative, but it positive, more work to do before transfusion
What is reverse typing?
- Using cells that are guaranteed to be A or B to look for a patient’s predicted isoagglutinins
What is forward typing?
- Using Anti bodies to make sure blood is specified type of antigen
What is the HAB test?
“Coomb’s test”
- Detects Ig and complement proteins on RBCs
- Visual RBC agglutination used to observe proteins on RBCs
- AHG “Antihuman globulin” makes agglutination visible
What is AHG?
“Antihuman globulin” reagent
- Made in animals
- Used to observed agglutination
- Bind to Igs that are attached to antigens on RBCs on their distal FC portion
- Only when enough RBCs with Ig are bound by AHG can there be observable agglutination
What is indirect antiglobulin testing?
“Antibody screen”
- Detects if Ig or complement are attached to RBCs
- Used to assess antigen antibody reactions
What is sensitization of RBCs?
- Mixing plasma with screening cells in vitro to get antibodies to bind
- When we add AHG, they agglutinate
What are the required pre transfusion compatibility tests?
- Typing: determine ABO and RH
a. Forward: for antigen detection
b. Reverse: for isoagglutinin testing - Screening: test for unexpected RBCs or antibodies
- Cross match
- History check
What does blood bank do when type and screen ordered?
- Determines ABO and RH by mixing ptn RBC with known reagents
- Visually assesses reactivity via agglutination
- Screen by mixing ptn. unknown plasma with RBCs of known phenotypes using AHG
What does positive screen necessitate?
Antibody identification of which ptn. antibody is reacting with the known RBCs
What is a type and crossmatch?
Same as type and screen EXCEPT:
- RBC units are allocated and labeled for delivery for ptn.
- **Do this is there is high likelihood ptn. will require blood
What is a DAT?
- Ptn. has been given blood they formed antibodies against
- Mix Ptn. blood post transfusion with AHG to see if agglutination occurs
- A positive test is abnormal!
When is DAT positive?
- Immediate IV hemolytic transfusion rxn
- Delayed, EV hemolytic transfusion rxn
- Hemolytic disease of newborn
- Autoimmune hemolytic anemia
What to do if person is given wrong RBC bag?
- Stop transfusion
What happens when ptn. given wrong blood?
- Acute hemolytic rxn
- Ptn preformed IgM attack donor RBCs leading to intravascular hemolysis via complement activation
- DAT will be positive in hemolysis is incomplete from attached IgG or C3b
- Positive most of the time
What is haptoglobin?
- Protein made in liver that will attempt to mop up free hemoglobin from bursting of RBCs
- Finite amount of haptoglobin is exhausted quickly
What happens in IV hemolytic rxn.?
- Hemoglobin released and bound by haptoglobin
- Immune complexes exploded into blood from cell membranes
Signs of IV hemolytic rxn.?
- Fever
- Flank Pain
- Hemoglobinuria
4 HYPOtension
5 Renal failure - Bleeding
What is responsible for attacking RBC?
C9 attack complex
What do C9 do?
Drills holes in RBCs leading to hemolysis
What do C3a and C5a?
Responsible for vasodilation leading to hypotension in complement activation
What leads to hypotension in complement activation?
C3a and C5a activation causing vasodilation
What leads to renal failure in IV hemolysis?
- Massive vasodilation from C3a / C5a
- Clogging of glomerulus from lysed RBCs / complex
What leads to DIC IV hemolysis?
- Complement activation factor XII
- Consumption of coag factors and platelet depletion
Major catastrophic effects in IV hemolysis?
- Renal Failure
- Hemoglobinuria / hemoglobinemia
- DIC: bleeding
- Hypotension
Which antibody usually involved in activating complement in IV hemolysis?
IgM
What are the characteristics of IV hemolysis?
WILL BE ON EXAM
- Occurs in circulation
- Antibody mediated: usually IgM
- Complement activation and involvement in RBC destruction
- Characteristic of acute hemolytic transfusion rxn
Where are wrong blood samples most often given?
Highly charged environments:
- ER
- ICU
- OR
2nd most common cause of death in transfusion?
- IV hemolysis due to ABO incompatibility
- From ptn. specimen misidentification
Primary or secondary immune response stronger?
- Secondary
- This occurs in delayed hemolysis
- Takes longer to occur but is stronger
How can patients be exposed to antigens they lack?
- Transfusion
- Transplant
- Pregnancy
Common laboratory markers in expected hemolysis?
MIGHT BE ON TEST*
- Falling hemoglobin (Hgb) and hematocrit (Hct)
- Hyperbilirubinemia
- Low or absent haptoglobin
- Elevated total LDH
- Direct Antiglobulin Test is positive
- MCV’s high due to reticulocytosis
- Peripheral blood smear findings
Characteristics of unexpected alloantibodies?
- IgG in nature
- Do not bind complement
- Cause EV hemolysis
- Slow kinetics
What test to give if you expect hemolytic transfusion rxn occurring?
- DAT
- Identify antibody for moving forward
How do sensitized RBCs leave body in EV hemolysis?
- Slowly, and usually through liver and spleen
What are the characteristics of EV hemolysis?
WILL BE ON EXAM
- Outside circulatory system: spleen/liver
- Antibody mediated: usually IgG
- Complement NOT activated
- Monocyte Fc receptor activated
- Characteristic of delayed transfusion rxn.
- Spherocytosis polychromasia
What are spherocytes and polychromasia characteristic of?
EV hemolysis
What are reticulocytes?
- Young RBCs in circulation
- Larger and lighter in color
- Means marrow is responding to hemolysis
