Patients’ chimeric antigen receptor ( CAR ) T cells’ expansion and persistence are linked to response, toxicity, and long-term efficacy. As a result, in order to maximize this therapeutic strategy, the tools used to identify CAR T cells after infusion are essential. Nevertheless, despite the importance of this crucial biomarker, there is a lot of variation in CAR T-cell detection techniques, as well as in the frequency and timing of testing. Additionally, layers of complexity that limit intertrial and interconstruct comparisons are added by heterogeneity in the reporting of quantitative data. In a scoping review, we used the PRISMA – ScR checklist to evaluate the heterogeneity of CAR T cell expansion and persistence data. 105 manuscripts were screened, and 60 were chosen for analysis based on the inclusion of CAR T – cell expansion and persistence data. The analysis focused on 21 clinical trials from the USA that used a Food and Drug Administration-approved CDT-cell construct or one of its predecessors. Flow cytometry and quantitative PCR were found to be the two main methods for identifying CAR T-cells across the range of constructs. The specific methods employed, however, were highly variable despite the appearance of uniformity in detection techniques. Quantitative data were frequently not reported, and both the number of detected and evaluated time points varied significantly. We examined all subsequent manuscripts reporting on the 21 clinical trials, recording all expansion and persistence data, in order to determine whether subsequent trials had resolved these problems. Although additional detection methods, such as droplet digital PCR, NanoString, and single-cell RNA sequencing andndash, were reported in follow-up publications, there were still discrepancies in terms of detection time and frequency and a sizable amount of quantitative data was still not readily available. Our findings emphasize the urgent need to create universal reporting standards for CAR T-cell detection, particularly in the early stages of research. Cross-trial and cross-CAR T-cell construct comparisons are very difficult due to the current reporting of non-interconvertible metrics and the limited availability of quantitative data. It is urgently necessary to establish a standardized method for gathering and reporting data, as doing so would significantly advance the ability of patients receiving CAR T-cell therapies to achieve better outcomes.