Thoracic duct injury resulting in abnormal newborn screen

Measurement of T-cell receptor excision circles (TREC) in neonates has allowed for population-based screening of severe combined immunodeficiency and other disorders associated with T-cell lymphopenia. In addition to primary T-cell lymphopenic disorders, secondary causes of T-cell lymphopenia can be diagnosed with TREC analysis. We discuss the diagnostic evaluation of a patient with normal TREC analysis at birth that became abnormal after cardiac surgery. TREC analysis was performed by the Florida State Laboratory. Diagnostic evaluation and treatment were performed at All Children's Hospital, St Petersburg, Florida. We identified a 38-day-old female patient with thoracic duct injury, which caused chylothorax and chylous ascites diagnosed after an abnormal newborn screen. Chylothorax was secondary to thoracic duct injury after cardiac surgery and led to severe lymphopenia and hypogammaglobulinemia. Thoracic duct ligation led to improved lymphocyte counts and normalization of immunoglobulin levels. Secondary causes of lymphopenia are detected with TREC assay that lead to abnormal newborn screen results. Many secondary causes of lymphopenia can be acquired with normal initial newborn screens that become abnormal over time.