Newborn Screening for Primary T- and B-Cell Immune Deficiencies—A Prospective Study in Andalucía

Background: Quantification of T-cell-receptor-excision circles (TRECs) and kappa-deleting-recombination-excision circles (KRECs) from dried blood spots (DBS) allows detection of neonates with severe T-cell and/or B-cell lymphopenia that are potentially affected by severe combined immunodeficiency (SCID), as well as X-linked agammaglobulinemia (XLA). Methods: Determination of TRECs and KRECs using a triplex RT-PCR (TRECS-KRECS-β-actin) assay from prospectively collected DBS between February 2014 and December 2016 in three hospitals in Seville, Spain. Cut-off levels were TRECs < 6/punch, KRECs < 4/punch and b-actin > 700/punch. Internal (SCID, XLA, ataxia telangiectasia) and external controls (CDC) were included. Results: A total of 8943 DBS samples obtained from 8814 neonates were analysed. Re-punching was necessary in 124 samples (1.4%) due to insufficient β-actin values (<700 copies/punch). Preterm neonates (GA < 37 weeks) and neonates with a BW < 2500 g showed significantly lower TRECs and KRECs levels (p < 0.001). Due to repeated pathological results, ten neonates were re-sampled (0.11%), of which five neonates (0.055%) confirmed the pathological results: one case was a fatal chromosomopathy (TRECs 1/KRECs 4); two were extreme premature newborns (TRECs 0/KRECs 0 and TRECs 1/KRECs 20 copies/punch); and 2 neonates were born to mothers receiving azathioprine during pregnancy (TRECs 92/KRECs 1 and TRECs 154/KRECs 3 copies/punch). All controls were correctly identified. Conclusions: Severe T- and B-cell lymphopenias were correctly identified by the TRECS-KRECS-β-actin assay. Prematurity and low BW are associated with lower TREC and KREC levels. Extreme prematurity and maternal immune suppressive therapy can cause false positive results of TRECs and KRECs values