Absolute Lymphocyte Count as a Surrogate for Lymphocyte Phenotype Analysis of CD3 Count in Monitoring Thymoglobulin Response Post Heart Transplantation

Purpose Dosing of Anti-thymocyte globulin therapy (ATG), used in the prevention and treatment of rejection, is optimally guided by CD3 levels. The purpose of this study was to establish the reliability of using Absolute Lymphocyte Count (ALC) as a substitute for CD3 given its ready availability and low cost. Methods A retrospective review was conducted of heart transplant recipients from 9/2014 to 2/2019 who received ATG and had a CD3 count with corresponding ALC. The Pearson correlation coefficient was used to examine the correlation between ALC and CD3. Validity tests and the Youden Index were performed to identify an appropriate range for an ALC cutoff that would provide the greatest degree of validity of ALC as an appropriate surrogate for a CD3 cutoff of 100 cells/mm3. Results 332 paired samples were collected. Analysis demonstrated correlation between ALC and CD3 count. The Pearson correlation coefficient was 0.45 (R-Square 0.23), p less than 0.0001. Validity testing of ALC of 200 cells/mm3 against CD3 counts 100 cells/mm3 showed sensitivity 0.635 (160/252), specificity 0.875 (70/80), positive predictive value (PV) 0.941 (160/170), and negative PV 0.432 (70/162). Based on the Youden index, the zone for the optimal cutoff points ranged from 100 to 200 cells (Figure 1). AUC for the ROC analysis was 0.81 (Figure 2). Conclusion This study suggests that ALC may have validity as a selective substitute for CD3 monitoring in patients receiving ATG. Further studies of this novel approach are warranted.