Flashcards in Transfusion Medicine I Deck (24)
What are all transfusion diseases associated with?
What test will be positive with transfusion diseases?
All immune hemolytic states are associated with a positive AHG (Coombs’) Test
- normally circulate and do not cause disease
- they are expected, “naturally-occurring”
Ex: A/B antibodies
- Ab against own species but not self
What are the most important aspects of blood transfusion?
• Specimen Identification
• Patient Identification
What is the Coombs' test?
Detects Ig or complement proteins on red blood cells with visible RBC agglutination used to observe proteins
attached to the RBCs
AHG is a serum made by purposely immunizing non-
human animals to human Ig and/or complement proteins
Indirect Antiglobulin Test
D￼￼etects Ig or complement proteins attached to RBCs in vitro. It is positive when IgG from the patients serum attaches to human RBCs which is visualized with the addition of the Coombs' (AHG) reagent
What is blood typing?
The determination of the type of blood (A/B/O) and the Rh factor of the blood.
What is blood screening?
Test for unexpected clinically significant red blood cells antibodies
The screen is the admixture of patient’s unknown plasma with RBCs of a known phenotype.
How is blood type determined?
“Reactivity” is physically visually assessed by agglutination with admix patient’s RBCs with known typing reagents (anti-A, anti-B and anti-D)
What is the usual result of a blood screen?
They are usually negative.
What must be done with a positive blood screen result?
A positive screen result requires an antibody identification
What is a crossmatch?
Admix patient’s plasma with blood donor’s red blood cells
When is a typing and screen done?
When the need for transfusion is remote
Ex: Surgical patients with low risk of bleeding
When is a typing and crossmatch done?
Patients with a high likelihood that RBC transfusion will be required
Ex: Actively bleeding patients
Direct Antiglobulin Test
Detects Ig or complement attached to RBCs in vivo in situations where RBCs are sensitized while in circulation
What are examples of situations where the DAT will be positive?
- Immediate (intravascular) hemolytic transfusion reactions
- Delayed (extravascular) hemolytic transfusion reactions
- Hemolytic disease of the fetus / newborn
- Autoimmune hemolytic anemias
Acute Intravascular Hemolysis
IgM’s lead to intravascular hemolysis via the complement activation with RAPID loss of RBCs.
What is the 2nd most common cause of death in blood transfusion?
Acute Intravascular Hemolysis - Due to ABO incompatibility with patient or specimen misidentification
What are 3 mechanisms where individuals can be exposed to alloantigens that they lack?
What are lab signs of hemolysis?
• Falling hemoglobin (Hb) and hematocrit (Hct)
• Low or absent haptoglobin
• Positive DAT
Delayed Extravascular Hemolysis
SLOW RBC destruction due to IgG formation against an unexpected alloantigen with extravascular hemolysis (spleen/liver). Complement is usually NOT active.
Future transfusions must honor the alloantibody, by providing RBC’s negative for that antigen.