Table 3. Types of assays and their examples under FDA classifications.

Type of Assay	Purpose of the Assay	Example
Companion diagnostic (CDx)	Essential for safe and effective use of the corresponding therapeutic product	Herceptin® with HercepTest™, Zolgensma® with MEBCDX AAV9 test (Japan only) Roctavian with AAV5 Detect CDx™
Complementary diagnostic	Identifies a subset of patients that may respond better to the drug. Not essential for the safe and effective use of the drug	Imfinzi® with Ventana PD-L1 (SP263) assay
Class Companion Diagnostic or Class Complementary Diagnostic	Can be used for multiple products within a therapeutic class	Cobas® EGFR Mutation Test v2 with Tarceva®, Tagrisso®, Iressa®, Gilotrif®, and Vizimpro® for the treatment of EGFR mutated NSCLC
In vitro diagnostic (IVD), 510(K) CLEARED	Assay used to diagnose, monitor, or prevent disease. This category includes both CDx and assays not linked to a therapeutic product	Total immunoglobulin E (IgE) for allergy testing, AdvanSure™ SARS-CoV-2 IgG (RBD) for SARS-CoV-2 immune response testing
Laboratory developed test (LDT)	Not commercially available as a distributed kit. Can only be performed at laboratory where developed. Can be used for patient management decisions and clinical end points	AAV9 antibody tests at Athena Diagnostics (US), at ImmunoSpot (US), and Viroclinics (EU)
Bioanalytical assay	Exploratory clinical trial endpoint. Not used for patient management decision	PK, PD, ADA, Biomarker assay, evaluated retrospectively.

This table was originally published in ‘Preexisting antibody assays for gene therapy: Considerations on patient selection cutoffs and companion diagnostic requirements’ by Braun, Lange, Schatz et al. (2024). Available at: https://www.sciencedirect.com/science/article/pii/S2329050124000330.

This table was modified and reused with permission from the publisher, licensed under the Creative Commons Attribution – NonCommercial-NoDerivs (CC BY-NC-ND 4.0). https://creativecommons.org/licenses/by-nc-nd/4.0/