necessarily represent the views of the funding agency.”
Genetics and Public Health in the 21st Century
EVALUATION OF GENETIC TESTING
Newborn Screening Quality Assurance
W. Harry Hannon, L. Omar Henderson, Carol J. Bell
Newborn Screening Quality Assurance Program, Division of Environmental Health Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, 4770 Buford Hwy, MS F19, Atlanta, GA 30341
In 1961, blood collected as a dried spot on filter paper was first introduced by Dr. Robert Guthrie in New York for testing newborns for phenylketonuria (PKU).1 He coupled the specially collected specimen with a unique bacterial inhibition test that he developed for phenylalanine.2 This combination of easily transportable specimens and inexpensive tests made large scale testing for PKU possible. The first case of PKU detected by this procedure occurred in a pilot study in New York after the testing of 800 newborns.1 The first application of the population-based newborn screening for PKU using this unique specimen collection and test system was initiated in Massachusetts in the fall of 1962 with the testing of most newborns in the state.3 The successful introduction of dried-blood spots (DBSs) for PKU screening led to the development of population screening of newborns nationwide with the use of blood drops collected by a heel stick and absorbed into filter paper. The ease of transporting the DBSs made them ideal specimens for large-volume testing by regionalized laboratories for population-based screening.
Today, newborn screening is the largest genetic testing effort in the nation and is primarily performed by state public health laboratories. The detection of treatable, inherited metabolic diseases is a major public health responsibility. Screening tests are designed to sort newborns who probably have a disease from those who do not. These tests are not intended to yield a diagnostic testing outcome. However, effective screening of newborns, with the use of DBS specimens collected at birth, combined with follow-up diagnostic studies and treatment, helps prevent mental retardation and premature death. These blood specimens are routinely collected from more than 95% of all newborns in the nation. State public health laboratories or their associated laboratories routinely screen DBS specimens for inborn errors of metabolism and other disorders that require intervention.
In 1975, the Committee for the Study of Inborn Errors of Metabolism, National Academy of Sciences, stated that greater quality control of PKU screening is essential and recommended that a single laboratory within CDC be responsible for maintaining the proficiency of the regional laboratories testing newborns for PKU.4 For more than 20 years, the Centers for Disease Control and Prevention (CDC), with its cosponsors, the Health Resources and Services Administration and the Association of Public Health Laboratories, has conducted research on materials development and assisted laboratories with the quality assurance (QA) for these DBS screening tests. The heart of these efforts, the Newborn Screening Quality Assurance Program (NSQAP), is a voluntary, nonregulatory program designed to help participating laboratories evaluate and improve the quality of their testing and to foster the standardization of newborn screening services nationwide. The success of any external proficiency-testing (PT) program depends on the full participation of all laboratories that have similar responsibilities. Most laboratories that test DBS specimens participate voluntarily in the NSQAP. The QA services of the NSQAP primarily support newborn screening tests performed by state laboratories; however, the program also accepts other laboratories, manufacturers of test kits, and international participants.
Newborn screening for PKU and congenital hypothyroidism is carried out in all 50 states, the District of Columbia, and Puerto Rico.5,6 Galactosemia and hemoglobinopathies (e.g., sickle cell disorders) are the disorders that are next most frequently screened for. The number and type of other disorders screened for vary from state to state. One private laboratory offers supplemental testing for over 20 disorders.
QA is an active system of setting criteria for the quality of performance required for each step in the overall newborn screening process to ensure adequate confidence in each procedure. Quality control (QC) is the mechanistic procedure for monitoring adherence to the set QA criteria, for establishing corrective action when the criteria are not met, and for documenting the assay's performance and corrective actions taken.7 The QA and QC operations are complex because of the number of steps, facilities, and personnel involved. Centralization of screening facilities and operations reduces the complexity somewhat and produces a more controllable operation and a system with reduced risk for failures. Although laboratories serve as the focal point for the identification of presumptive positive cases, the laboratories and the analytical methods they use constitute only one of the QA elements in the screening process.7
Laboratory QA criteria are set primarily for three steps associated with analytical performance: ensuring adequate specimen volume, eliminating false-negative identifications, and minimizing the number of false-positive detections to a cost-effective range. By applying QC principles to analyses, the laboratory staff can monitor analytical variables and if the analytical system fails, effectively target corrective steps to ensure quality and improve performance. Laboratories primarily use two types of QC applications to monitor their QA criteria: internal and external actions. Internal QC is referred to as bench-level QC and is an important process for routinely monitoring the stability of the analytical performance. External QC is most often referred to as PT or performance evaluation. Regularly participating in an external PT program and keeping records of this performance is the best means by which laboratories can show their quality of performance. Internal and external QC efforts are complementary activities and key elements of any laboratory QA system.7
An effective QA system must be based on realistic criteria for high-quality analytical and overall laboratory performance. This permits a laboratory to set and monitor, through its QC parameters, the daily achievement rate of these standards of performance. A fully operational QA system also allows for interlaboratory comparisons of analytical precision and relative bias. Performance criteria for the newborn screening laboratory must be predetermined and recorded as part of the written QA protocol. The QA system enables the laboratory to qualitatively rate the validity and credibility of its performance.
All newborn screening testing must be done by laboratories licensed by their respective states and must meet the requirements of the Clinical Laboratory Improvement Amendments of 1988 (CLIA'88). As part of these requirements, a screening laboratory must meet certain criteria for QC and must participate in PT programs. PT is used to evaluate the quality of the measurement process on a periodic basis, usually quarterly. PT specimens are to be handled and analyzed the same as patient specimens. Laboratories must satisfactorily participate in a Health Care Financing Administration (HCFA)-approved PT program (if available) for each method they use to analyze human specimens. In the absence of a HCFA-approved PT program for newborn screening, the NSQAP enables laboratories to meet the CLIA quality-assurance requirement for verifying test accuracy. If a PT program is not available for a specific newborn screening test, laboratories must have a system for verifying the accuracy and reliability of their test results at least twice a year. Laboratories can develop a self-administered PT program using available reference methods and materials. This PT program will be administered by a quality assurance officer who is not in the participating laboratory. The laboratories must then document their performance in this self-administered type PT in a QC manual, which is available for review.
HCFA-approved PT providers must meet set criteria. One requirement is the availability of a performance-grading scheme. The analytical values of DBS assays for newborn screening cannot be reasonably applied to the grading of tests because of the intrinsic variance (e.g., spot size, hematocrit, elution) of the specimen type, the inherent purpose of screening, and the sorting of the population tested. Therefore, error judgements for a grading scheme for screening laboratories should be based on either the presumptive clinical assessment or the sorting of positive and negative outcomes.
The Newborn Screening Quality Assurance Program (NSQAP) at the CDC in Atlanta, Georgia, provides services for laboratories that use DBS specimens to perform newborn screening tests. The mission of this program is to improve interlaboratory comparability and to work toward interlaboratory standardization. Current participants include newborn screening laboratories, confirmatory testing laboratories that use DBS tests, diet-monitoring laboratories, and manufacturers of testing products. The NSQAP interacts with state-affiliated newborn screening programs and the manufacturing community to (1) maintain laboratory methods, (2) evaluate and distribute reference and QC materials, (3) evaluate QC systems available to user laboratories, (4) conduct training and/or provide consultative services, and (5) develop mechanisms for the voluntary evaluation of laboratory performance, the transfer of new and improved technology, and the evaluation of programs screening for hypothyroidism, phenylketonuria, other inborn metabolic disorders, and hemoglobinopathies. Figure 1 shows the number of program participants in the QC and PT program components for each disorder. The NSQAP provides QC materials, PT services, and technical support to 64 domestic screening laboratories, 20 manufacturers of diagnostic products, and 122 laboratories in 33 foreign countries.
QA programs enable screening laboratories to achieve high levels of technical proficiency and maintain continuity despite changes in commercial assay reagents while maintaining the high-volume specimen throughput that is required. Laboratories that misclassified a PT specimen are provided immediate notification and consultation to resolve the analytical problem. Through interactive efforts, NSQAP and screening laboratories continually strive to improve program services in order to better meet the growing and changing needs of newborn screening activities in the public health community and to help ensure equivalent high-quality testing by these programs nationwide. Besides the two DBS distribution components, the program contains a filter paper evaluation component for the QA of this product. Methods developed by the NSQAP are used to evaluate and compare different production lots of filter paper from commercial sources.
Although the DBSs were used successfully in semiquantitative assays (i.e., bacterial inhibition assays) for newborn screening, the DBS matrix encountered mixed reports of adequate performance when quantitative assays for congenital hypothyroidism were introduced. A significant problem was that the variance contributions of the filter-paper matrix were not realized fully, and consequently they were not minimized and contained for use in quantitative assays. Standardizing the filter-paper matrix for performance parameters has contributed substantially to our confidence in its reliability and to the acceptance of DBSs as a specimen matrix for a variety of new applications and technologies.
The collection of DBS specimens for newborn screening and other related applications requires special grades of commercially manufactured paper as a unique whole-blood collection matrix. In the United States, only papers approved by the Food and Drug Administration (FDA) are acceptable for blood collection for clinical tests. Critical to proper and effective use of this matrix is an ongoing assessment and evaluation of new production lots as they are manufactured, as well as the monitoring of problems identified with individual lots in use by state-affiliated newborn screening programs. Since the paper-punch size selected from a blood spot is used as a volumetric sample for quantitative analysis, a high degree of uniformity is essential.
The NSQAP and the two FDA-approved manufacturers have reached an agreement whereby the NSQAP is provided with statistically valid sample sets from each new production lot of filter paper for evaluation by standardized procedures8 before the new lot is released to the user community. Each year the NSQAP evaluates, with the extensive cooperation of manufacturers (Schleicher & Schuell, Inc., Keene, NH, and Whatman, Inc., Fairfield, NJ), new lots of paper approved by FDA for blood collection. Each manufacturer is responsible for establishing its own evaluation laboratory that uses the same procedures as the ones used by the NSQAP. After all parties conducting independent evaluations of the filter-paper lot agree that the lot is acceptable, the lot is released for distribution. The independent evaluations by the NSQAP are an impartial and voluntary service offered as a function of the QA program and do not constitute preferential endorsement of any product over other specimen-collection papers approved by FDA. The specific role of the NSQAP in this evaluation process includes (1) evaluating manufactured lots of filter-paper products for physical parameters, serum absorption volume, homogeneity, and absorption time; (2) monitoring the performance of new production lots relative to previous lots; (3) maintaining criteria for certification of paper lots used by screening laboratories; (4) maintaining a controlled historical storage center of papers previously approved for newborn screening; and (5) reporting the outcomes of these evaluations to the user community. Standardization is required both for within-lot and lot-to-lot performance of filter paper to help ensure reliable analytical transitions and comparability of calibrators, patient specimens, and QC materials. The volumetric aliquots of serum contained in a punch size from a DBS are affected by several variables, including the paper thickness, the volume of blood applied, the humidity, the printing process used to produce blood-collection forms, the handling during specimen collection, the blood absorption time, and the storage environment for the paper.9,10
In the future, other commercial sources of FDA-approved filter paper for specimen collection may become available in the United States. Theoretically, if the performance criteria8 are met, the transition between commercial sources of paper should not be different from the transition between lots from the same source. Because screening programs have limited experience with the impact of multiple sources of filter paper on performance, they should sort the specimens by filter paper source for analysis and closely monitor performance parameters until they are confident in the new product. Soon the screening community could be coping with calibrators, patient specimens, and control materials on filter paper from different commercial sources. The screening programs must be cautious and include monitoring for each parameter in their QC operations.
Most of the specimen-collection facilities have selected DBS specimens collected by a heel stick as the method of choice for newborn screening. However, procedures are also available for applying blood collected in capillary tubes and by dorsal vein puncture onto the preprinted circles of filter paper. Although these methods are not the preferred choice, they are now considered to be rational alternatives to direct application from the newborn's heel-stick site.7 The DBS has the advantage of being simple and easy to handle as well as posing fewer biological hazards than liquid specimens.
A national standard has been developed for the uniform collection of quality DBS specimens from newborns.8 This standard specifically defines how to collect blood onto filter paper, specifications for the specimen matrix, specimen shipping requirements, and other parameters. Screening laboratories routinely monitor the quality of collected specimens against their established criteria of acceptance and rejection. The primary justification for refusing to analyze a specimen and declaring it unacceptable is that its analysis may yield unreliable, misleading, or clinically inaccurate values for a particular analyte. Since, by this definition, unacceptable specimens give no usable information, such specimens should not be analyzed; and those responsible for collecting the specimens should be informed so that an acceptable specimen can be obtained as soon as possible.8 The collection of unacceptable specimens delays the analysis and potentially the treatment of affected newborns.
The NSQAP prepares and distributes to laboratories worldwide more than 250,000 DBSs per year. The manufactured DBS materials must simulate, as closely as possible, the actual specimens for the assay systems. Dried-blood materials that are prepared for QC and PT are certified for homogeneity, analyte accuracy, stability, and suitability for all assays from different commercial sources. The NSQAP distributes DBS materials used in screening tests for congenital hypothyroidism, PKU, galactosemia, congenital adrenal hyperplasia, homocystinuria, maple syrup urine disease (MSUD), biotinidase deficiency, and hemoglobinopathies. These materials must be stable under the routine conditions of shipment, laboratory logistics, analysis, and storage, and must be homogeneous enough that their variance will not contribute significantly to the analytical variance of the methods and their detection outcomes. The concentration of analyte in the control materials must cover the range of normal and abnormal specimens tested by the screening process and include a low-level analyte specimen with which to monitor the analytical sensitivity of the methods.7
The NSQAP prepares "zero-base" whole-blood pools for DBS materials by gently mixing washed, outdated Red Cross-packed red blood cells with clean-filtered serum to yield a whole-blood pool with a hematocrit of 55%. Portions of the pool are enriched with the desired analyte at predetermined concentration levels. Each portion is then uniformly applied to approved filter-paper cards in 100-µL aliquots, air-dried horizontally overnight, packed in sealed bags with desiccant, and stored at -20 oC. Blood collected from any source, including cord blood, that is prepared for use in the production of QC and PT materials must be negative for HIV, hepatitis, and other infectious agents. Documentation of the source, composition, homogeneity, and stability of all DBS materials as well as the procedure(s) used to assign their expected or target values are available upon request from the NSQAP. Specimens from newly prepared production lots of DBS materials are checked for stability and tested to ensure their homogeneity and the accuracy of their assigned concentration values.
To ensure that laboratories receive representative sheets of the production batch, the NSQAP uses a random number table to select the set of DBS sheets for each laboratory. QC shipments are distributed semiannually and include the blood-spot sheets, instructions for storage and analysis, and data report forms. Data from five analytical runs of each lot and shipment are compiled in the midyear and annual summary reports that are distributed to each participant. The reported QC data are summarized and show the analyte by series of QC lots, the number of observations, mean values, and the standard deviations by kit or analytical method. In addition, NSQAP used a weighted linear regression analysis to examine the comparability by method of reported versus enriched concentrations. Results of the linear regression analyses (Y-intercept and slope) for all lots within an analyte set are summarized in the reports. The mean value and the within-laboratory and total standard deviations are calculated for each concentration within a QC lot for a specific analyte. The summarized QC data provide information about method-related differences in analytical recoveries and method-related biases. Because each QC lot series is prepared from a single batch of hematocrit-adjusted, nonenriched blood, the endogenous concentration of a given analyte is the same for all specimens in a lot series. The Y-intercept of the regression analysis for reported values provides a measure of the endogenous analyte concentration. For amino acid-enriched DBS materials, participants measure the endogenous concentration levels by analyzing the nonenriched QC lots (the base pool). The values for the Y-intercept and the base pool are similar for most methods. Ideally, the slope should be 1.0, and most slopes calculated for reported data are close to this value. Because the endogenous concentration is the same for all QC lots within a series, it should not affect the slope of the regression line among methods. Generally, slope values substantially different from 1.0 indicate that a method has an analytical bias. Figure 2 shows an example of mean values of reported results for phenylalanine measurements by different methods used for linear regression analysis. These data routinely compiled by NSQAP help participants understand the performance of different methods and to select appropriate test methods and kits in the future.
For the PT component, designing evaluation materials that fairly assess screening laboratory performance is difficult because of the variable cutoff values both within and among laboratories. The NSQAP analyzed this problem and concluded that the only equitable method by which all laboratories could be evaluated, is one that is based on the first decision level (cutoff) for separating test results that require follow-up testing from negative test results that do not. This initial decision (cutoff) value should be an important part of the routine reporting scheme for all participants even though it will differ among laboratories. All PT panels contain five blind-coded specimens, each consisting of 100-µL blood spots. Specimens in the PT panels either contain endogenous levels or are enriched with predetermined levels of thyroxine, thyroid-stimulating hormone, phenylalanine, total galactose, 17 "-hydroxyprogesterone, leucine, or methionine. Special separate panels for biotinidase deficiency and galactose-1-phosphate uridyltransferase deficiency are prepared with purchased blood from donors with enzyme deficiencies. The DBS specimens for sickle cell disorders and other hemoglobinopathies are prepared from residual cord blood provided to the QA program by the Alabama and Georgia newborn screening programs.
In quarterly reports the NSQAP summarizes the quantitative data and clinical assessments for all data received from PT program participants by the due date. Because some of the pools in a routine PT survey represent a unique donor specimen, differences in endogenous materials in the donor specimens are important parameters for assessing performance and method-related differences. Presumptive clinical classifications (based on quantitative data) of some specimens may differ by participant because of specific clinical-assessment practices. Only the qualitative assessments are reported for the sickle cell disorders and other hemoglobinopathies. Table 1 shows the results for phenotype and clinical assessment misclassifications reported for hemoglobinopathies in 1998.
For those participants who provide their cutoff values, the NSQAP applies these cutoffs in the final appraisal of the error judgment. The errors for qualitative assessments in the PT component are split into misclassifications and transcription errors. Transcription errors continue to be a major error component in the PT surveys. Transcription errors are monitored to provide an indication of attention to detail by laboratory personnel. In 1998 data, the number of false-positive misclassifications exceeded the number of transcription errors and false-negative misclassifications for most disorders. The NSQAP calculates the rates for false-positive classifications on the basis of the number of negative specimens analyzed; the false-negative classifications are based on the number of positive specimens analyzed. Screening programs are designed to avoid false-negative reports; this precautionary design, however, may be the cause of many of the false-positive classifications.11 False-positive classifications are a cost-benefit issue and a credibility factor with follow-up programs.11 False-positive rates should be monitored and kept as low as possible. Figure 3 shows the total number of classification and transcription errors made by domestic and foreign laboratories that screened for selected disorders in 1998. For most disorders, the number of errors was greatest for foreign laboratory participants.
The introduction of tandem mass spectrometry to newborn screening has greatly expanded the potential number of disorders detectable by routine newborn screening with the DBS specimen. Over 15 disorders could be added to the present screening profiles, some of which raise many issues about follow-up and treatment of affected newborns. The most important of these disorders appears to be medium-chain acyl-CoA dehydrogenase deficiency (MCAD), a defect in the oxidation of fatty acids. The reported prevalence of MCAD is 1 in 10,000.12 However, no external quality assurance program is now available for the measurement of acylcarnitines by tandem mass spectrometry for detection of these disorders. Laboratories using tandem mass spectrometry will need to operate and document quality assurance efforts within their respective facilities according to the CLIA regulations for situations where no PT programs are available.13 A laboratory must have a system for verifying the accuracy and reliability of its test results at least twice a year. If a laboratory performs the same test on different instruments or methodologies, a mechanism must be established to evaluate and define the relationship between test results. The laboratory must have documentation of all quality assurance activities, including problems and corrective actions taken, and must maintain accurate record-keeping.13
DNA testing for cystic fibrosis (CF) is carried out by only a few state newborn screening programs, but there is a growing interest by other programs. Specimens used to monitor the quality of testing should closely simulate the actual routine clinical specimen. Historically, these materials have been prepared by analyte enrichment (or spiking of normal base biological matrices) or from materials obtained from donors afflicted with the disorder or genetic defect being tested for. Presently, two PT surveys (non-HCFA approved) operate with worldwide participation for QA of CF testing: the CAEN QA Survey (France) and the Human Genetics Society of Australasia's Newborn Screening Quality Assurance Program (New Zealand).14 The Australasian QA Program offers PT services for DNA testing for CF ()F508). However, the preparation method for DNA QA materials used in these programs does not appeal to some participants because detection depends on the compatibility of the primers used in the )F508 assay with the amplicons. Determining the number of DNA mutations screened for as part of CF detection and whether QA materials can effectively simulate these mutations are unanswered questions. Efforts are ongoing to improve these QA test materials so that they provide better method harmonization and better simulation of the CF mutations.
The development of simulated materials through specific DNA-probe spiking of specimens is problematic for assessing the equivalency of performance for all test systems. Materials that harmonize for all test systems are essential to performance assessments of DNA tests. This is a difficult challenge because of the underlying analytical variables; but until such PT materials with the required mutations are developed, meaningful performance data are difficult to gather for the CF test and other emerging DNA tests for newborn screening. One possible solution to this dilemma is the development of unique evaluation processes for DNA tests. Perhaps such a process could assume that a laboratory's performance on any one mutation test adequately measures its performance on all similar DNA testing performed during the PT assessment window. This and other possible options need study and development by experimental trials within the DNA-testing community.
With the expanding interest in the use of DBSs for DNA testing, newborn screening programs are faced with many decisions regarding leftover patient specimens. Advances in mechanisms to obtain sufficient quantities of DNA from DBSs and to apply the polymerase chain reaction (PCR) technology allow numerous genetic tests to be performed on a single DBS.15 Presently, a few states have retained more than a million leftover specimens. The length of storage time varies among national screening programs. Figure 4 shows, by state, the length of time that leftover specimens are stored. The value of retained DBSs is directly related to the documentation and care with which they are stored.16,17 When newborn screening programs decide to store leftover DBSs for long time intervals, they must take scientifically sound and justifiable approaches to all aspects of storage. To ensure the validity of stored specimens, they should develop a storage policy and design a QA system. If the analytes (mutations) for which the DBSs are being saved are known, then appropriate assayed QC materials should be included.16 All QC materials must be handled and stored with the specimens under identical processing conditions. The QC materials should be randomized in the storage system to prevent location bias. Compromised or potentially tainted specimens have no scientific value. Flow charting the process and using barcode identifications are useful in tracking the specimen. Systems for easy access and retrieval should be design components of the storage system. A program should also document storage conditions for QA records. Uncontrolled storage and release could produce compromised specimens and other problems. In addition, programs should formalize operations for handling leftover specimens; however, only a few screening programs have written guidelines for the release and use of stored specimens.16 Consent requirements for extended use of screening specimens are unclear. Some programs use informed refusal or lack of dissent. Clarifications of the legal and ethical questions are important to the use and release of leftover DBS specimens.16
External QA programs provide participants with information on the specificity of methods used, on accuracy of calibration systems in use, and on their and other participants'overall compliance with specific performance quality goals.7 Reliance on the technical consultative and statistical support services of sponsoring PT surveillance programs and on shared data and expertise among screening laboratories is vital for improved analytical performance of individual laboratories as well as for interlaboratory standardization. Laboratory testing goals for newborn screening are met through the analysis of only a single DBS specimen from each newborn. The time frame for this critical testing and assessment is limited, and the outcome of a false-negative result has serious medical and legal consequences.18 External QC testing must meet special criteria that define the quality of results needed to make a clinical decision and must vary with the disorder screened for, the analyte measured, and the method used. Moreover, these statistical interpretations of short windows of observations for analytical test results are not altogether satisfactory and must be balanced by rigorous review and evaluation procedures for all internal and external QC measures.7 Each step must be thoroughly documented to facilitate review and evaluation, more readily identify sources of analytical error, and effectively resolve detected problems. Good quality assurance practices and quality improvement ensure that all data, conclusions, and reports derived from those data are technically sound and legally defensible.18
QA programs are designed to help screening laboratories achieve excellent technical proficiency and maintain confidence in their performance while processing large volumes of specimens daily. The NSQAP continually strives to produce certified DBS materials for reference and QC analysis, to improve the quality and scope of services, and to provide immediate consultative assistance. Through the interactive efforts with participants, the NSQAP and other QA programs aspire to meet the growing and shifting needs arising from the rapidly changing profile of national newborn screening efforts and from the introduction of advanced technologies applied to DBS testing.
We thank the staff members of the NSQAP for their dedication and service to our program participants worldwide: Barbara Adam, Ricky Alexander, Kami Borsellino, Sarah Brown, Hugh Gardner, Roberta Jensen, Dr. Joanne Mei, Nancy Meredith, and Dr. F.W. Spierto.
Use of trade names is for identification only and does not imply endorsement by the Public Health Service or the U.S. Department of Health and Human Services.
- Guthrie R. The origin of newborn screening. Screening 1992;1:5-15.
- Guthrie R, Susi A. A simple phenylalanine method for detecting phenylketonuria in large populations of newborn infants. Pediatrics 1963;32:338-43.
- MacCready RA. Phenylketonuria in screening programs. N Engl J Med 1963;269:52-6.
- National Academy of Sciences. Genetic screening: programs, principles, and research. Washington (DC): The Academy, 1975:91.
- Hiller EH, Landenburger G, Natowicz MR. Public participation in medical policy-making and the status of consumer autonomy: the example of newborn-screening programs in the United States. Am J Public Health 87;1997:1280-8.
- Newborn Screening Committee, The Council of Regional Networks for Genetic Services (CORN). National Newborn Screening Report - 1995. Atlanta (GA): in press.
- Slazyk WE, Hannon WH. Quality assurance in the newborn screening laboratory. In: Therrell BL Jr, editor. Laboratory methods for neonatal screening. Washington (DC): American Public Health Association, 1993:23-46.
- Hannon WH, Boyle J, Davin B, Marsden A, McCabe ERB, Schwartz M, et al. Blood collection on filter paper for neonatal screening programs - third edition: approved standard. Wayne (PA): National Committee for Clinical Laboratory Standards; 1997 NCCLS Document LA4-A3.
- Slazyk WE, Phillips DL, Therrell BL Jr, Hannon WH. The effect of lot-to-lot variability in filter paper on the quantification of thyroxin, thyrotropin and phenylalanine in dried-blood specimens. Clin Chem 1988;34:53-8.
- Arends J. Neonatal screening using dried blood spotted on filter paper: methodological factors which contribute to imprecision. In: Therrell BL Jr, editor. Advances in neonatal screening. Proceedings of the 6th International Neonatal Screening Symposium; 1986 Nov 16-19; Austin (TX). Amsterdam: Elsevier Science Publishers B.V., 1987:549-50.
- Therrell BL Jr, Panny SR, Davidson A, Eckman J, Hannon WH, Henson MA, et al. U.S. newborn screening system guidelines: statement of the Council of Regional Networks for Genetic Services. Screening 1992;1:135-47.
- Ziadeh, R, Hoffman EP, Finegold DN, Hoop RC, Brackett JC, Strauss AW, Naylor EW. Medium chain acyl-CoA dehydrogenase deficiency in Pennsylvania: neonatal screening shows high incidence and unexpected mutation frequencies. Pediatr Res 1995;37:675-8.
- Federal Register. 1992, Feb 28;57(40):7150-85.
- Centers for Disease Control and Prevention. Newborn screening for cystic fibrosis: a paradigm for public health genetics policy development-proceedings of a 1997 workshop. MMWR 1997;46(No. RR-16):13-4.
- McCabe ERB. Utility of PCR for DNA analysis from dried blood spots on filter paper blotters. PCR Meth Appl 1991;1:99-106.
- Therrell BL Jr, Hannon WH, Pass KA, Lorey F, Brokopp C, Eckman J, et al. Guidelines for the retention, storage, and use of residual dried blood spot samples after newborn screening analysis: statement of the Council of Regional Networks for Genetic Services. Biochem Mol Med 1996;57:116-24.
- McEwen JE, Reilly PR. Stored Guthrie cards as DNA banks. Am J Hum Genet 1994;55:196-200.
- Andrews LB, editor. Legal liability and quality assurance in newborn screening. Chicago: American Bar Foundation, 1985:29-73.
Figure 1. The number of participants for components of the quality assurance program in 1998.
Figure 2. Comparison of mean reported concentrations by method for phenylalanine quality control materials.
Figure 3. The summary of performance evaluation errors by domestic and foreign laboratories in 1998.
Figure 4. The length of time that leftover newborn screening dried-blood-spot specimens are kept by state screening programs.
Table 1: Errors reported by participants of the Sickle Cell Disease and Other Hemoglobinopathies Program in 1998
Transcription Errors __________________0.1%
Clinical Assessment Misclassifications_____0.9%
Labs Making Transcription Errors________1
Labs Misclassifying Specimens__________5
Labs Correctly Classifying Specimens_____47
52 Laboratories - 1040 Assayed Specimens