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Newborn screening (NBS)3 has been acclaimed by the Centers for Disease Control and Prevention as one of the most successful public health programs of the 21st century (1 ). In 2013, we celebrated the 50th anniversary of NBS, and these 50 years were marked by many successes. An estimated 200 million newborns in the US have been screened during that period for at least 1 disorder, phenylketonuria. Today's screening effort detects ^10 000 newborns with certain heritable disorders from the 4 million screened annually. Most of these disorders cause severe, nonreversible harmful effects if not identified and treated before the onset of symptoms (2). NBS programs have evolved as new technologies have been introduced from covering 1 disorder to presently 33 recommended disorders in the US (3, 4 ).
All NBS programs in the US collect blood samples on US Food and Drug Administration- cleared filter papercollection devices(5). Only2 commercial sourcesare presently approved for use in device production and dried blood spot (DBS) collection. The filter papers, Whatman Grade 903 and Ahlstrom Grade 226, are made from high-purity cotton linters and manufactured to yield accurate and reproducible blood samples according to the Clinical and Laboratory Standards Institute's specifications (NBS01-A6) (5). Under controlled conditions, the filter paper blood collection device for NBS can achieve the same level of precision and reproducibility expected from clinical methods that typically use blood collected in vacuum tubes or capillary pipettes (6 ). Unlike these liquid collection devices, filter paper exhibits different levels of imprecision, but these can be characterized and then harmonized to minimize the variation it contributes to measurements (6 ).
Simplicity of collection, transport, and storage makes DBS samples an economical preference for many clinical applications. However, poor-quality filter paper and improperly collected DBS may significantly alter the performance of NBS, yielding poorer test results, the risk of missed cases, and delays in testing, each creating the need for a replacement sample and a possibly delayed diagnosis. Delays in the screening process can cause issues with the achievement of desired criteria for turnaround time, i.e., time from sample collection to result reporting, and ultimately to diagnosis and start of treatment (5 ).
It was not until filter paper became widely used in population-based screening that the routine evaluation...