CHT Crossmatch Procedures & Interpretation 3

Question 1

A donor-specific antibody (DSA) detected by single antigen bead assay with an MFI of approximately 3,000-5,000 would most likely produce which crossmatch results?

Accepted Answer

Negative CDC crossmatch but positive flow cytometric crossmatch

Answer

Moderate-strength DSAs are detectable by the highly sensitive FCXM but may be below the complement-fixing threshold needed for a positive CDC crossmatch result.

Question 2

A historical (peak) crossmatch uses archived recipient serum to:

Accepted Answer

Detect prior sensitization events that may no longer be reflected in current serum

Answer

Historical serum represents the recipient's peak sensitization and is tested to uncover antibodies that may have waned but could return (anamnestic response) after transplantation.

Question 3

On the standard NIH CDC scoring scale, a score of 8 indicates:

Accepted Answer

81–100% cytotoxicity (strongly positive result)

Answer

The NIH CDC scale runs from 1 (negative, 0–10% dead cells) to 8 (strongly positive, 81–100% dead cells), with higher scores indicating more extensive complement-mediated lysis.

Question 4

Which crossmatch technique has the LEAST sensitivity for detecting donor-specific antibodies?

Accepted Answer

Standard CDC crossmatch without wash steps

Answer

Standard CDC crossmatch requires sufficient antibody to activate the full complement cascade; it is the least sensitive, while SAB, FCXM, and AHG-CDC can all detect lower antibody concentrations.

Question 5

In a standard CDC crossmatch protocol, which source of complement is most commonly used?

Accepted Answer

Exogenous rabbit serum added as an external complement source

Answer

Exogenous rabbit serum is the standard complement source in CDC crossmatch because it is potent and consistent; relying on human serum complement yields variable and often insufficient activity.

CHT - Certified Histocompatibility Technologist Practice Test

CHT - Certified Histocompatibility Technologist Practice Test

CHT Crossmatch Procedures & Interpretation 3