Hematologic and Clinical Characteristics Distinguishing Persistent and Transient Idiopathic T Cell Lymphopenia

Objective Newborn TREC screening has identified infants with idiopathic T cell lymphopenia (TCL) with no known associated genetic factors. By convention, lymphopenia resolves by 12 months of age in transient TCL. We aim to characterize demographic, laboratory, maternal and perinatal health characteristics that differentiate infants with transient vs. persistent idiopathic TCL. Methods A single-center retrospective analysis was performed on patients born from September 2010 through August 2021. Chart review was performed through August 2022 on 53 eligible infants with abnormal TREC screening at corrected gestational age 37 weeks or greater. Descriptive statistics were calculated for initial TREC levels and T cell lymphocyte counts at initial referral. Two-sample t-tests and Wilcoxon rank-sum tests were used to assess continuous data. Fisher’s exact test assessed associations between transient and persistent TCL patients and selected health characteristics and risk factors of both mother and baby. Results When comparing the percentage of CD3 cells out of total lymphocytes, transient TCL babies demonstrated higher percentages than persistent TCL babies (61.1 +/- 13.4% and 48.5 +/- 14.6%, p = 0.002). Absolute CD3 levels were higher in transient compared with persistent (2011.5 +/- 678.7 cells/µL vs 1279.5 +/- 539.6 cells/µL, p < 0.0001). Percent of CD4 of total lymphocytes were higher in transient compared with persistent TCL babies (42.7 +/- 12.6% vs 34.5 +/- 12.1%, p = 0.02), in addition to percent of CD8 of total lymphocytes (17.5 +/- 6.0 % vs 13.1 +/- 5.1%, p = 0.006). Absolute lymphocyte counts on a concurrent CBC sample were also higher in transient (4.2 +/- 1.4 K/µL vs 3.1 +/- 1.2 K µL, p = 0.005) than persistent TCL subjects. Moreover, transient TCL patients were less likely to be on any medications or supplements compared with their persistent counterparts: 18/25 (72%) of those taking medications were persistent compared with 10/28 (35%) transient subjects (p = 0.013). No other statistically significant associations were discovered. Discussion Babies with idiopathic TCL show distinct hematologic characteristics on initial screening that could predict duration of lymphopenia. The use of medications is associated with longer duration of disease; however, the reasons for this are unclear.