Pathology Cheat Sheet
Make Compatibility Explicit
Blood banking for NEET-PG: ABO and Rh systems, universal donor, crossmatching, direct vs indirect Coombs test, and component therapy with cryoprecipitate.
MedNext Academy | 3 min read
Make Compatibility Explicit
Blood banking for NEET-PG: ABO and Rh systems, universal donor, crossmatching, direct vs indirect Coombs test, and component therapy with cryoprecipitate.
The ABO and Rh blood group systems, compatibility testing, and the appropriate use of blood components.
High-yield lines
- The ABO gene on chromosome 9 encodes a glycosyltransferase that adds a terminal sugar onto the H antigen.
- ABO antibodies are naturally occurring and cause immediate complement-mediated intravascular haemolysis if incompatible.
- Group O red cells are the universal red cell donor, and group AB plasma is the universal plasma donor.
- The Rh D antigen is the most immunogenic red cell antigen and drives haemolytic disease of the newborn.
- Blood grouping tests red cells with known antisera and serum against known cells in reverse grouping.
- Crossmatching mixes recipient serum with donor cells to detect incompatibility before transfusion.
- The indirect Coombs test detects free antibody in serum and is used in antibody screening and crossmatching.
- The direct Coombs test detects antibody already bound to red cells in vivo.
- Component therapy separates each donation into packed red cells, platelets, plasma, and cryoprecipitate.
- Packed red cells treat symptomatic anaemia, platelets treat thrombocytopenia, and fresh frozen plasma treats coagulopathy.
- Cryoprecipitate is rich in fibrinogen, factor VIII, and von Willebrand factor.
- Component therapy targets the specific deficit and reduces volume load and antigenic exposure.
Mapped competency codes
- PA22.1
- PA22.2
- PA22.3
- PA22.4
Continue into the full chapter
This summary maps to PA22-blood-banking-and-transfusion.
Frequently Asked Questions
Why do ABO-incompatible transfusions cause immediate haemolysis?
Because ABO antibodies are naturally occurring IgM that activate complement, producing rapid intravascular haemolysis of incompatible donor red cells.
What is the difference between the direct and indirect Coombs tests?
The direct test detects antibody already bound to red cells in the patient, while the indirect test detects free antibody in the serum, as used in crossmatching.
Which blood component contains fibrinogen and factor VIII?
Cryoprecipitate, which is enriched in fibrinogen, factor VIII, and von Willebrand factor.
Who is the universal red cell donor?
Group O, because O red cells lack A and B antigens and are not agglutinated by recipient anti-A or anti-B antibodies.
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