Ad hoc antibody modification of a validated flow cytometric immunophenotyping panel—recommendations and safeguards for clinical laboratories

Immunophenotyping by flow cytometry is a valuable test providing important information in a timely manner. In clinical laboratories, it is performed using validated antibody panels designed to ensure consistent and accurate results. However, unforeseen situations, such as unique or unusual immunophenotypes, or supply chain issues, may necessitate ad hoc modifications to these panels. This manuscript provides guidance for performing minor modifications, such as substituting or adding one or two antibodies, while maintaining the integrity of the assay. These modifications are intended for rare clinical situations and are not substitutes for the full validation protocols outlined in CLSI H62. An example of this would be a patient with a rare, but not uncommon, situation in which a B cell lymphoma lacks expression of CD19, CD20, and surface light chains, such that the lineage of the neoplastic cells cannot be determined without a straightforward addition or substitution of another marker into a laboratory's available panel. The recommendations and best practices herein aim to optimize patient care by allowing laboratories to adapt to unique clinical scenarios without compromising assay performance and are not a way to permanently modify the assay. Key considerations include assessing the impact on fluorescence compensation, antibody binding, assay sensitivity, and overall assay performance. The manuscript provides limitations for the extent of modifications, examples, and troubleshooting strategies to ensure reliable results when ad hoc changes are made. Proper documentation with review and approval by laboratory medical directors is recommended to mitigate risks associated with these modifications.