Blood Banking and Transfusion Services (Immunohematology)
Blood banking tests whether you can turn serologic reactions into a safe transfusion decision. MLT items in this domain center on ABO/Rh typing, antibody detection and identification, compatibility testing, component selection, and transfusion reaction workup. Most questions give you a result pattern and ask what it means or what you do next.
ABO and Rh typing
- Forward (cell) typing uses patient red cells against anti-A, anti-B, anti-D; reverse (serum) typing uses patient serum against A1 and B reagent cells. Both must agree, and reaction strength and phase must be recorded.
- Expected reverse: group A has anti-B; group B has anti-A; group O has both; group AB has neither.
- Any forward/reverse discrepancy is resolved before crossmatch: repeat on a new sample, check for rouleaux (saline replacement disperses it), acquired B antigen, anti-A1 in an A2 patient, or missing antibodies in a newborn or immunosuppressed patient.
- Weak D testing is required on donor units; for patients it is done per policy, typically when Rh immune globulin eligibility is at issue. Weak D donors are labeled D-positive.
Antibody detection and identification
- The antibody screen uses group O reagent cells tested by indirect antiglobulin technique (IAT); a positive screen triggers a panel, an autocontrol, and often enzyme-treated or selected cells.
- Rule out by pattern: reactive cells share an antigen that nonreactive cells lack, and the patient's own phenotype must lack that antigen to make the antibody possible.
- Clinically significant, AHG-reactive antibodies include anti-D, anti-K, anti-Jka, anti-Fya and anti-S; anti-I is a cold autoantibody reacting at room temperature and is usually not significant.
- A positive autocontrol suggests autoantibody or a delayed hemolytic reaction; always check transfusion history.
Components and storage
- Red cells: 1-6 degrees C, 42 days in additive solutions, 35 days in CPDA-1.
- Platelets: 20-24 degrees C with continuous agitation, 5 days.
- Fresh frozen plasma: at or below -18 degrees C for up to 12 months.
- Irradiated components for immunocompromised recipients; washed or leukoreduced units for severe reaction histories.
Worked example
A group O, D-positive patient has a positive antibody screen in all three screen cells at AHG with a negative autocontrol. A 10-cell panel reacts with 3 of 10 cells; every reactive cell is Jk(a+) and every nonreactive cell is Jk(a-). Patient phenotyping shows Jk(a-). Reasoning: the negative autocontrol points to an alloantibody rather than autoantibody; the perfect antigen association plus the patient's Jk(a-) phenotype identifies anti-Jka. Select Jk(a-) units and perform an AHG crossmatch.
Traps that cost marks
- Rouleaux and cold agglutinins read as panagglutination; saline replacement or prewarmed technique exposes the truth.
- Assuming an ABO discrepancy can be overridden by the forward type alone.
- Choosing antigen-negative units without confirming the patient's own phenotype.
- Missing the clerical check, the single most common cause of an acute hemolytic reaction.