CHT Antibody Detection & Characterization

Question 1

Which assay platform is the current gold standard for HLA antibody detection and specificity determination in US transplant labs?

Accepted Answer

Luminex-based Single Antigen Bead (SAB) assay

Answer

Complement-dependent cytotoxicity (CDC) PRA

Answer

ELISA-based PRA panel

Answer

Western blot

Question 2

What does a prozone effect (hook effect) in Luminex SAB testing refer to?

Accepted Answer

High antibody concentrations cause falsely low MFI due to steric inhibition of detection

Answer

Very low antibody concentrations produce falsely elevated MFI

Answer

Complement in serum activates beads producing false positives

Answer

The assay reaches maximum fluorescence and cannot distinguish concentrations

Question 3

How does EDTA treatment of serum improve HLA antibody detection in Luminex SAB assays?

Accepted Answer

It chelates calcium to inactivate complement, preventing complement-mediated bead interference

Answer

It denatures IgM antibodies to isolate IgG only

Answer

It removes lipids that interfere with bead binding

Answer

It reduces background fluorescence from non-specific binding

Question 4

What is the significance of a 'mean fluorescence intensity' (MFI) threshold in SAB assay interpretation?

Accepted Answer

MFI values above the threshold are considered positive for antibody presence and used to define DSA

Answer

MFI directly measures antibody concentration in mg/mL

Answer

MFI values below the threshold indicate tolerance

Answer

MFI is only used for CDC crossmatch interpretation

Question 5

Which HLA antibody class is most commonly detected in sensitized transplant patients?

Accepted Answer

IgG

Answer

IgM

Answer

IgA

Answer

IgE

Question 6

What is a 'Panel Reactive Antibody' (PRA) test historically designed to detect?

Accepted Answer

Antibodies in a patient's serum reactive against a panel of randomly selected donor lymphocytes

Answer

The percentage of viable lymphocytes in a donor panel

Answer

Autoantibodies against patient's own HLA

Answer

Complement levels in post-transplant serum