**Background:** Newborn screening (NBS) began in 1963 with Robert Guthrie's bacterial inhibition assay for phenylketonuria (PKU) using dried blood spots (DBS) on filter paper cards, a collection method still used worldwide. Over six decades, NBS has expanded from single-disorder testing to multiplex platforms capable of detecting dozens of conditions. The authors frame NBS within the principle that 'all screening programmes do harm, some do good as well, and, of these, some do more good than harm at reasonable cost,' making continuous improvement in specificity and sensitivity essential.
**Methods:** This is a narrative review synthesizing historical developments and recent innovations in NBS. The authors draw on published literature, international survey data (e.g., from Europe, the USA, South-East Asia, Latin America), and ongoing research programs. They describe the evolution of analytical techniques—from bacterial inhibition and immunoassays for congenital hypothyroidism (CHT), congenital adrenal hyperplasia (CAH), and cystic fibrosis (CF) to tandem mass spectrometry (MS/MS) in the late 1990s/early 2000s, which enabled simultaneous analysis of over 60 metabolites from a single DBS punch. The review covers quality assurance practices (volumetric standardization, calibration, internal and external quality control), second-tier testing strategies, emerging 'omics' technologies, artificial intelligence/machine learning applications, and the integration of DNA-based methods including next-generation sequencing (NGS).
**Key Results:** The authors report that in Europe (51 countries surveyed), 47 screen for PKU, 46 for CHT, 25 for CF, 24 for CAH, and 7 for SCID. The introduction of MS/MS shifted the paradigm from 'one spot—one test—one disorder' to 'one spot—one test—many metabolites for many disorders.' By 2010, data from 11,000 NBS disorders were collated globally through the CLIR (Collaborative Laboratory Integrated Reports) multivariate analysis system, which has been shown to reduce false-positive rates and improve positive predictive values. The quantification of T-cell receptor excision circles (TRECs) by PCR in 2010 introduced frontline DNA-based screening for severe combined immunodeficiency (SCID). Spinal muscular atrophy (SMA) screening, detecting SMN1 exon 7 deletions, became the first NBS test for a disorder with no biochemical footprint in blood. Two large studies found that whole exome sequencing (WES) had 'overall lower sensitivity and specificity when compared to routine NBS.' Ongoing large-scale programs include Screen4Care (European, predicted 18,000 participants using custom panels) and the UK Newborn Genomes Programme (predicted 100,000 participants using WGS). The authors note that worldwide, more than 40 million babies receive some form of NBS annually, but this represents only about 30% of children born globally. In developed countries, NBS uptake typically exceeds 99%.
**Clinical Implications:** The authors emphasize that technological advances—particularly NGS, proteomics, and metabolomics—offer unprecedented opportunities but also introduce risks: identifying carriers, variants of uncertain significance (VUS), late-onset disease presentations, and pseudodeficiencies. They stress that second-tier testing (e.g., chromatographic separation, DNA analysis) can significantly reduce false positives; for example, measuring methylmalonic acid (MMA) as a second-tier test for propionic aciduria/methylmalonic aciduria has 'vastly improved' screening and reduced unnecessary recalls. Quality assurance must evolve in parallel with new techniques: volumetric standardization remains a key issue (the previously assumed 3.1 µL blood volume per 3.2 mm punch has been contradicted by recent gravimetric studies), and there are currently no commercially available DBS-based external calibrators. The authors advocate for patient-based real-time quality control (PBRTQC), noting that NBS 'lends itself perfectly' to this approach given its defined and consistent population. They call for agreed-upon case definitions, standardized treatment protocols, interoperable disease registries for long-term outcome studies, and international collaboration through bodies like the International Society for Neonatal Screening (ISNS) and Screen4Rare. A key caution is that new approaches must not undermine public confidence: 'when using approaches where the significance of the findings for the individual child may be unclear, public confidence regarding effective treatments offering benefits to the affected child is undermined.' The authors conclude that an expert advisory group recognized by the European Commission could provide informed, unbiased advice to support national health policymakers.