RESUMEN
BACKGROUND: Early diagnosis of primary immunodeficiency such as severe combined immunodeficiency (SCID) and X-linked agammaglobulinemia (XLA) improves outcome of affected children. T-cell-receptor-excision circles (TRECs) and kappa-deleting-recombination-excision circles (KRECs) determination from dried blood spots (DBS) identify neonates with severe T- and/or B-lymphopenia. No prospective data exist of the impact of gestational age (GA) and birth weight (BW) on TRECs and KRECs values. METHODS: TRECs and KRECs determination using triplex RT-PCR (TRECS-KRECS-ß-actin-Assay) from prospectively collected DBS between 02/2014 and 02/2015 in three hospitals in Seville, Spain. Cut-off levels were TRECs < 6/punch, KRECs < 4/punch and -ß-actin>700/punch. Internal (SCID, XLA, ataxia telangiectasia) and external controls (NBS quality assurance program, CDC) were included. RESULTS: A total of 5160 DBS were tested. Re-punch was needed in 77 samples (1.5%) due to insufficient ß-actin (<700 copies/punch). Pre-term neonates (GA<37 weeks) and neonates with a BW<2500 g showed significantly lower TRECs and KRECs levels (p < 0.001). Due to repeat positive results five neonates were re-called (<0.1%): Fatal chromosomopathy (n = 1; TRECs 1/KRECs 4); extreme pre-maturity (n = 2; TRECs 0/KRECs 0 and TRECs 1/KRECs 20 copies/punch); neonates born to mothers receiving azathioprine during pregnancy (n = 2; TRECs 92/KRECs 1 and TRECs 154/KRECs 3 copies/punch). All internal and external controls were correctly identified. CONCLUSIONS: TRECS-KRECS-ß-actin-Assay correctly identifies T- and B-cell lymphopenias. Pre-maturity and low BW is associated with lower TREC and KREC levels. Extreme pre-maturity and maternal immune suppressive therapy may be a cause for false positive results of TRECs and KRECs values, respectively. To reduce the rate of insufficient samples, DBS extraction and storage need to be improved.