Blood Bank
Core concepts
ABO typing pairs the forward group (patient cells plus reagent anti-A and anti-B) with the reverse group (patient serum plus A1 and B cells); any discrepancy must be resolved before a unit is issued. Rh(D) typing with a weak-D check is required on donors, not routinely on patients. Antibody detection uses the indirect antiglobulin test (IAT) with enhancement (LISS, PEG, or gel); identification panels depend on rule-out and on dosage, since homozygous cells express more antigen. A full AHG crossmatch is needed when the screen is positive or there is a prior antibody history; an immediate-spin or electronic crossmatch is acceptable only when the screen is negative and the history is clear.
Storage essentials
RBCs 1-6 C for up to 42 days in additive solution; platelets 20-24 C with continuous agitation for 5 days; FFP and cryoprecipitate at -18 C or colder for 12 months. Emergency release is group O (Rh-negative when feasible).
Traps
- Absent reverse grouping in a newborn is normal; isohemagglutinins appear at 3-6 months.
- A2 and A2B patients may form anti-A1, which is not clinically significant.
- Cold autoantibodies such as anti-I cause discrepant reverse typing and panreactive screens; prewarm or cold-adsorb.
- Rouleaux from myeloma or high globulin mimics agglutination; saline replacement disperses it.
- Bombay (Oh) cells lack H antigen and react with everything.
- A positive DAT does not by itself prove hemolysis.
Worked example
Patient is group A with a positive screen identified as anti-D. Issue A-negative (D-negative) packed RBCs, crossmatched to AHG compatibility.