CHT Crossmatch Procedures & Interpretation 2

Question 1

Flow cytometric crossmatch (FCXM) is considered more sensitive than standard CDC crossmatch because:

Accepted Answer

It detects antibody binding directly, independent of complement fixation

Answer

It uses a larger volume of recipient serum in each test run

Answer

It only requires T cells, simplifying cell preparation

Answer

It uses fresh rather than frozen archived serum samples

Question 2

In a flow cytometric T-cell crossmatch, a positive result is typically defined by:

Accepted Answer

A fluorescence channel shift exceeding the laboratory-defined threshold vs. negative control

Answer

Greater than 10% of T cells showing cell death by 7-AAD exclusion

Answer

Greater than 50% of T cells showing surface antibody binding

Answer

An MFI lower than the negative control sample

Question 3

A positive B-cell crossmatch with a concurrent negative T-cell crossmatch most likely indicates:

Accepted Answer

Anti-HLA class II antibodies directed at DR, DQ, or DP antigens

Answer

Anti-HLA class I antibodies directed at HLA-A, B, or C antigens

Answer

ABO blood group incompatibility

Answer

Nonspecific complement activation from aggregated immunoglobulin

Question 4

A 'virtual crossmatch' in transplantation is performed by:

Accepted Answer

Comparing recipient antibody specificities (from solid-phase assay) against the donor's HLA type

Answer

Using computer modeling to simulate complement-mediated lysis in silico

Answer

Generating in vitro donor cell lines from stored DNA for physical testing

Answer

Testing recipient serum against a virtual panel of 100 random donor cells

Question 5

EDTA is sometimes added to crossmatch reaction tubes in order to:

Accepted Answer

Chelate divalent cations to inhibit complement activation

Answer

Enhance HLA antigen expression on lymphocyte surfaces

Answer

Preserve lymphocyte viability during extended incubation

Answer

Reduce nonspecific binding of the secondary fluorescent antibody

Question 6

The antihuman globulin (AHG)-enhanced CDC crossmatch increases sensitivity by:

Accepted Answer

Crosslinking IgG bound to cell-surface HLA, increasing complement-fixing complexes

Answer

Replacing the requirement for rabbit complement entirely

Answer

Specifically targeting IgM antibodies in the recipient serum

Answer

Reducing false-positive results caused by autoimmune antibodies

Question 7

Which cell preparation is most appropriate as a target for a T-cell crossmatch?

Accepted Answer

Peripheral blood T lymphocytes isolated by rosetting or immunomagnetic separation

Answer

Washed red blood cells isolated from donor whole blood

Answer

Bone marrow-derived dendritic cells from the donor

Answer

Donor-derived platelet-rich plasma