Article

Effect of specimen collection method on newborn screening for PKU

California Department of Health Services, Genetic Disease Branch, 2151 Berkeley Way, Annex 4, Berkeley, CA, 94704, USA
Screening 08/1994; 3(2):57–65. DOI: 10.1016/0925-6164(94)90001-9

ABSTRACT Introduction: Although heelstick followed by direct spotting of blood on filter paper is usually the method of choice for routine newborn screening of phenylketonuria (PKU) and other disorders, current National Committee for Clinical Laboratory Standards (NCCLS) recommendations provide guidelines for blood collection by capillary tube and dorsal vein, finding that these methods are acceptable alternatives. These latter methods are used for newborn blood collection by a number of hospitals in the US. In large newborn screening programs, however, standardization and cutoffs are set by large-scale testing of specimens collected by direct spotting on filter paper. Methods: Three separate groups of 21 149, 111 035, and 120 837 newborn filter paper specimens were analyzed for phenylalanine concentration by a fluorometric method to determine the effect of collection method of phenylalanine values. The three methods examined were direct spotting of blood from heelstick on filter paper, collection of blood into capillary tube with transfer to filter paper and dorsal hand venipuncture with transfer to filter paper. Results: The mean phenylalanine levels were 2.63 mg/dl, 2.46 mg/dl, and 2.28 mg/dl for direct spotting, capillary tube, and dorsal hand vein, respectively. Actual presumptive positive rates for the three methods were , and , respectively. These differences were consistent when controlling for laboratory and Area Genetic Center (AGC) origin. Discussion: Since guidelines generally recommend or require direct spotting, values obtained by this method should remain the standard for setting cutoffs; deviations from this method could lead to missed cases, particularly for early-tested infants with borderline elevated values.

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