Transfusion medicine Flashcards
1
Q
Definitions of blood transfusion tests
A
- Type (ABO, Rh+/-) and screen (Abs the patient has against any blood group
- Abs will either be naturally occurring (such as ABO Abs, do not require exposure to another’s blood), or blood exposure stimulated (such as Rh Abs, which required exposure to another’s RBC Ags)
- Crossmatch: done before a transfusion is given. Donor blood and recipient serum or plasma are combined
- If the two agglutinate or hemolyze then the two are not crossmatch compatible
- DAT (Coomb’s or direct Ag test): detects IgG or complement that coats the RBCs
- IAT (indirect Ag test): detects RBC Abs that are circulating in plasma unbound to red cells. Used to identify if patient has Abs to a RBC group
2
Q
Major blood groups
A
- AKA human erythrocyte Ags (HEAs)
- Most important ones: ABO, Rhesus (Rh), Kidd, Kell, Duffy
- All are proteins (Ag expression controlled directly by the gene) except ABO, which is a carbohydrate (expression of Ag controlled by genes that produce glycosyl transferases, on both chrom 9 and 19)
- Blood Ags can be whole proteins, polymorphisms of proteins (Rh), or terminal sugars (ABO)
3
Q
ABO blood group 1
A
- Some people express ABO blood groups (have H Ag), others do not (have h)
- H= gene that codes for fucosyltransferase (puts a fucose sugar onto a precursor substance on RBC membrane, producing H Ag)
- h= no gene coding for fucosyltransferase (bombay phenotype), leads to no Ag expression on RBC membrane
- ABO Ags are also expressed on platelets
4
Q
ABO blood group 2
A
- Once H is expressed it can be modified by other glycosyltransferases based on their expression
- H is required to have ABO blood type, if a person has h gene they do not have an ABO type
- If the H is modified w/ a terminal N-acetylgalactosamine (via that transferase), then you will have type A blood
- If the H is modified w/ a terminal galactose (via that transferase), then you will have type B blood
- If the H is unmodified then you will have type O blood
5
Q
ABO blood group 3
A
- ABO Ags can be modified or removed: some infectious agents secrete deacetylases into the blood
- These can deacetylate the A Ag (N-acetylgalactosamine to galactosamine), making it look nearly identical to the B Ag
- This may lead to hemolysis if the person’s B Abs then attack their RBCs
- A person has Abs against the opposite blood group (A has B Abs, B has A Abs, O has both, and AB has none)
- These Abs are naturally occurring (expected)
- Fetal-maternal ABO incompatibility is where a mother and fetus have different and opposing ABO types
- Not dire b/c ABO type expression doesn’t happen on RBC surface until 2 years
6
Q
Rhesus Ag
A
- There are multiple Rh Ags (D, C, E, e, c) but by far most important is D
- Having the D Ag on RBCs is called Rh positive
- Absence of the D Ag is Rh negative
- Rh protein is required for RBC shape and survival
- People can also have weakly expressed D Ag (Du), a D variant (Dv, where there is at least one AA substitution), DEL, and False D+
- Rh Ags are not expressed on platelets
- Insertion of Rh Ags depends on presence of Rh associated glycoprotein (RHAG)
- Mutations in RHAG lead to no expression of Rh and a condition called somatocytosis (hemolytic)
7
Q
Mutations in D Ag
A
- Weak D expression occurs when there is an AA substitution within or below the cytoplasmic domain of the RhD protein
- This leads to decreased abundance of D expression (weak D or Du), but exposure to normal D does not result in alloimmunization to normal D
- AA substitutions in the extra-cellular portion of RhD lead to a change in the accessible conformation
- These D variants appear different than normal D, and thus exposure to normal D can lead to alloimmunization to normal RhD
- DEL: Rh+ but D is expressed at such a low level they appear Rh-
- False D+: truly Rh- but falsely type Rh+
8
Q
Rh hemolytic disease
A
- Someone who is Rh negative will make Abs against RhD Ag ONLY if they are exposed to Rh+ blood
- Of newborn: mother is Rh- but fetus is Rh+. Mother must have been exposed to Rh+ blood in the past for complications to arise (otherwise she will not have Ab’s against Rh+, however the current pregnancy can induce the formation of anti-D Abs)
- It is possible to prevent an unexposed Rh- mother from making Rh+ Abs by injecting her w/ anti-D Abs before and after birth
9
Q
Platelet Ags
A
- 3 types of platelet Ags
- Ags found only on platelets: HPA (human platelet Ags) are glycoproteins on platelets divided in to systems (HPA1, 2, ect)
- Ags found on platelets and nucleated cells: HLA (MHC) class 1
- Ags found on platelets and RBCs: ABO groups
- Platelets DO NOT express Rh
- Ab’s against HPA leads to autoimmune or idiopathic thrombocytopenia purpura
10
Q
RBC Abs
A
- AutoAbs: Abs directed against one’s own Ags
- AlloAbs: Abs directed against foreign Ags, ones not found in the person’s blood
- Allos can be expected (naturally occurring) as in ABO Abs or unexpected (exposure stimulated) as in Rh, Kidd, Kell, Duffy, platelet and WBC Ags
- If a person is given incompatible ABO blood the Abs will bind to the Ag on the incompatible blood and lead to intravascular hemolysis (via complement)
- If a person is given incompatible Rh blood the Abs will bind to the D Ag and lead to extravascular hemolysis
11
Q
Platelet Abs
A
- Anti-glycoprotein (HPA) Abs: these are always unexpected, and usually autoAbs
- Anti-HLA Abs: these are alloAbs that are unexpected (blood exposure stimulated)
- ABO Abs: expected (naturally occurring) alloAbs. They do not pose as serious of a threat for platelet matching as they do for RBC matching, however it is best to match platelet ABO for optimal results after transfusion
12
Q
Ags and Abs for WBCs, plasma, and cryoprecipitate
A
- WBC Abs: anti-HNA and anti-HLA
- These may trigger severe acute respiratory failure (TRALI) when given to incompatible patients by bingeing to pulmonary endothelium
- Plasma (given when patient needs coag factors): contains ABO Abs and dissolved ABO Ags, both of which can form immune complexes when given to incompatible patients
- Rh does not matter for plasma
- For cryoprecipitate (only clotting factors), there is very little plasma so ABO compatibility is not as important. But it should be attempted
13
Q
Transfusion compatibility guidelines
A
- For RBCs: must be ABO and Rh compatible (if Rh positive can receive any Rh type, if AB can receive any ABO type)
- For platelets: must be ABO compatible, preferably Rh compatible (if patient is Rh- and all you have is Rh+, use anti-D immunoprophylaxis to destroy and Rh+ RBCs that may be transfused)
- Also for platelets: select crossmatched HLA and HPA compatible (only necessary if recipient has Abs for HLA and/or HPA)
- DO NOT need Rh matching for platelets
- For plasma/cryo: must be ABO compatible, DO NOT need Rh matching
- Plasma compatibility is opposite of ABO (since we are dealing mostly with Abs, not Ags): O is universal acceptor (has both Abs already) and AB is universal donor (has no Abs)
