Primary Immunodeficiency Testing in a Massachusetts Tertiary Care NICU: Persistent Challenges in the Extremely Premature Population

BACKGROUND: Prematurity presents a diagnostic challenge in interpreting primary immunodeficiency (PID) testing. METHODS: We retrospectively reviewed the charts of all infants in our level IV referral NICU in Massachusetts with immunologic testing performed from 2006–2018. RESULTS: The overall rate of PID testing was enriched in our population, with 1% of admitted patients having extended immunologic testing. The addition of TREC newborn screening in Massachusetts in 2009 increased the proportion of infants tested for PID in our NICU by 3-fold (1.21% post-NBS vs 0.46% pre-NBS). A majority of the term and late preterm (T/LP, ≥ 34 weeks) infants (31 of 41, 76%) and very premature (VP, 29–33 weeks) infants (12 of 17, 71%) who had immune testing had a genetic diagnosis associated with secondary immunodeficiency or a PID. Most infants who were born extremely premature (EP, < 29 weeks) (25 of 29, 86%) had no identifiable cause of immunodeficiency besides prematurity, despite a mean postmenstrual age of 40.1 weeks at the time of testing. CONCLUSION: Persistent immune derangements were present within a subgroup of the extremely premature population through term postmenstrual age. EP infants with significant infectious history and abnormal immune testing at term-corrected age should be considered for genetic testing.