Background: Cytokine release syndrome (CRS) is a life-threatening toxicity of chimeric antigen receptor (CAR) T-cell therapy and there is a limited understanding of its risk factors. Known markers of severe CRS lack specificity or require central lab facilities, making them unsuitable for safety surveillance during trials. Using data from anti-CD19 CAR-T trials from the Medidata Enterprise Data Store (MEDS) we analyzed laboratory tests with repeated measurements to identify differences in trends that persist across a variety of study designs, sponsors and indications. Our aim was to capture the dynamic response to lymphodepletion (LD) and CAR-T infusion events in the time course values of laboratory markers and compare these in the severe CRS (grade 3 and higher) and non severe CRS groups. Methods: Subjects in the anti-CD19 CAR-T trials obtained from MEDS had relapsed or refractory disease in one of the following: B Acute Lymphoblastic Leukemia (B-ALL), Mantle Cell Lymphoma (MCL), Non-Hodgkin Lymphoma (NHL) and Diffuse Large B-cell Lymphoma (DLBCL). Laboratory markers with repeated measurements across all studies were included in the analysis. Response to LD, CAR-T infusion and the onset of hematologic recovery was modeled with piecewise linear splines with knots at the boundaries of the pre LD (-18d to LD), the LD - infusion and post infusion (1d to 6d and 6d to 18d) intervals using linear mixed effects regression. Results: The dataset consisted of 542 patients: 24.1% B-ALL, 44.4% NHL, 16.8% MCL, 14.6% DLBCL; mean age 54.8 (SE = 0.021) years, 67.7% males. 27.3% had CRS 3+ with a median time-to-event of 4.5 days. Average rates of change (units per day) for the severe CRS subjects in the pre LD, LD-infusion and post infusion intervals relative to the rest are shown (table). None of the markers had a significant relative rate of change prior to LD. The average change in Albumin, Platelets and Hematocrit was consistently lower in severe CRS patients. Conclusions: Longitudinal laboratory marker data may be used to derive predictors of severe CRS in patients undergoing anti-CD19 CAR-T therapy. While some of the laboratory markers discussed above corroborate earlier findings, modeling the pre and post infusion kinetics can yield novel markers with improved precision in severe CRS prediction and better patient safety.