Anti-idiotypic antibodies (anti-IDs) are an example of a specific critical reagent that have been developed to target the variable region of the therapeutic and used in bioanalytical assessment of the mAb . The development and selection of anti-IDs for the therapeutic mAb is a first key-step in the successful development of a clinical PK assay . However, several other factors can affect the performance of a PK assay even with optimized anti-ID reagents. Specifically, matrix interference on a PK assay's performance has been well documented and continues to be the primary roadblock in the development of a PK assay . The presence of soluble drug target can also interfere with the ability of the anti-IDs to bind to the therapeutic mAb and impact performance . This soluble target interference could result in an under-quantification of the mAb as the PK assay would only quantify the "(partial) free" levels of the therapeutic and not the total amount of drug including "bound" mAb. In addition to interfering molecules, the format and incubation times of the PK assay can also significantly impact the PK assay performance . Therefore, it is critical to account for all potential sources of interference on assay performance during the development of a clinical PK assay .