Results of the College of American Pathology/American College of Medical Genetics and Genomics external proficiency testing from 2006 to 2013 for three conditions prevalent in the Ashkenazi Jewish population

PURPOSE

The purpose of this study was to determine analytic performance of laboratories offering molecular testing for conditions such as Tay-Sachs disease, Canavan disease, and familial dysautonomia, which are prevalent in the Ashkenazi Jewish population.

METHODS

The College of American Pathologists and the American College of Medical Genetics and Genomics cosponsor molecular proficiency testing for these disorders. Responses from 2006 to 2013 were analyzed for accuracy (genotyping and interpretations).

RESULTS

Between 11 and 36 laboratories participated in each Tay-Sachs disease distribution. Samples tested per month were constant (2,900) from 2006 to 2011 but recently increased. Participants reporting <10 samples tested per month had longer turnaround times (42 vs. 7%, longer than 14 days; P = 0.03). Analytic sensitivity and specificity for US participants were 97.2% (95% confidence interval: 94.7-98.7%) and 99.8% (95% confidence interval: 99.1-99.9%), respectively. Of 11 genotyping errors, 2 were due to sample mix-up. Analytic interpretations were correct in 99.3% of challenges (956/963; 95% confidence interval: 98.5-99.7%). Better performance was found for Canavan disease and familial dysautonomia. International laboratories performed equally well.

CONCLUSION

These results demonstrated high analytic sensitivity and specificity along with excellent analytic interpretation performance, confirming the genetics community impression that laboratories provide accurate test results in both diagnostic and screening settings. Proficiency testing can identify potential laboratory issues and helps document overall laboratory performance.

Down syndrome screening: suitability of a WHO 5 standardized total hCG assay

OBJECTIVE

To determine how the adoption of the new WHO 5th International Standard (IS 07/364) will affect the suitability of total βhCG as a marker for second trimester Down syndrome screening, compared to the current WHO 3rd IS (75/537).

DESIGN AND METHODS

Assays employing both standards were evaluated on the Beckman Coulter DxI platform. Matched βhCG results from 232 fresh second trimester maternal serum samples were compared. In addition, stored samples from 51 Down syndrome and 251 matched control sera were also tested with both assays and results converted to weight-adjusted multiples of the median (MoMs). These results were combined with maternal age and the existing alpha-fetoprotein, unconjugated estriol and inhibin-A MoM levels to compute patient-specific Down syndrome risk.

RESULTS

Correlation between the two sets of results on fresh samples was high (r=0.993), but showed a proportional increase of 33% (95% CI 31% to 35%) in results using the new versus old assay across the range of measurements. βhCG results in the case/control dataset were also highly correlated (0.994) and showed a similar proportional increase (34%). After computing assay-specific MoMs, the resulting 'triple' and 'quadruple' Down syndrome risks were highly correlated, and resulted in no difference in either of the two detection rates (78% and 88%, respectively) or false positive rates (6.4%, 6.8%).

CONCLUSIONS

Laboratories using the DxI platform with the new total βhCG 5th IS assay will need to compute new reference (medians), but can expect no impact on the clinical validity of the associated Down syndrome screening programs.

Screening for Down Syndrome in the United States: Results of Surveys in 2011 and 2012

Context.—Participants in a College of American Pathologists external proficiency testing program for first and second trimester Down syndrome screening.

Objectives.—To determine the number of women screened for Down syndrome in the United States, along with the type of test received and to compare those results to earlier surveys in 1988 and 1992.

Design.—Questionnaires regarding the type and number of Down syndrome tests performed per month were completed by participants in early 2011 and again in early 2012.

Results.—After accounting for some of the missing responses, data from up to 131 laboratories indicated that 67% (2 764 020 of 4 130 000) to 72% (2012: 2 963 592 of 4 130 000) of US pregnancies received prenatal screening for Down syndrome. Second trimester tests were most common (2012: 60%; 1 770 024 of 2 963 592), followed by integrated (2012: 21%; 627 876 of 2 963 592), and first trimester (2012: 19%; 565 692 of 2 963 592). The 6 largest laboratories tested 61% of screened pregnancies and offered the widest array of tests, while the smallest 32 tested 1% and almost always offered only second trimester tests.

Conclusions.—The current population estimate of 72% pregnancies screened annually is higher than estimates from 1988 (25%) and 1992 (50%). Available testing choices are also more varied, and all testing methods perform better than those methods available 10 years ago. Clinicians should ensure that women are offered tests that follow recommended best-practice testing protocols, and screening laboratories should assess whether patient needs are being met.

The impact of maternal plasma DNA fetal fraction on next generation sequencing tests for common fetal aneuploidies

Maternal plasma contains circulating cell-free DNA fragments originating from both the mother and the placenta. The proportion derived from the placenta is known as the fetal fraction. When measured between 10 and 20 gestational weeks, the average fetal fraction in the maternal plasma is 10% to 15% but can range from under 3% to over 30%. Screening performance using next-generation sequencing of circulating cell-free DNA is better with increasing fetal fraction and, generally, samples whose values are less than 3% or 4% are unsuitable. Three examples of the clinical impact of fetal fraction are discussed. First, the distribution of test results for Down syndrome pregnancies improves as fetal fraction increases, and this can be exploited in reporting patient results. Second, the strongest factor associated with fetal fraction is maternal weight; the false negative rate and rate of low fetal fractions are highest for women with high maternal weights. Third, in a mosaic, the degree of mosaicism will impact the performance of the test because it will reduce the effective fetal fraction. By understanding these aspects of the role of fetal fraction in maternal plasma DNA testing for aneuploidy, we can better appreciate the power and the limitations of this impressive new methodology.

Three-year experience of a CAP/ACMG methods-based external proficiency testing program for laboratories offering DNA sequencing for rare inherited disorders

PURPOSE

Thousands of genetic tests are now offered clinically, but many are for rare disorders that are offered by only a few laboratories. The classic approach to disease-specific external proficiency testing programs is not feasible for such testing, yet calls have been made to provide external oversight.

METHODS

A methods-based Sequencing Educational Challenge Survey was launched in 2010, under joint administration of the College of American Pathologists and the American College of Medical Genetics and Genomics. Three sets of Sanger ABI sequence data were distributed twice per year. Participants were asked to identify, formally name, and interpret the sequence variant(s).

RESULTS

Between 2010 and 2012, 117 laboratories participated. Using a proposed assessment scheme (e.g., at least 10 of 12 components correct), 98.3% of the 67 US participants had acceptable performance (235 of 239 challenges; 95% confidence interval: 95.8-99.5%) as compared with 88.9% (136 of 153; 95% confidence interval: 82.8-93.4%) for the 50 international participants.

CONCLUSION

These data provide a high level of confidence that most US laboratories offering rare disease testing are providing consistent and reliable clinical interpretations. Methods-based proficiency testing programs may be one part of the solution to assessing genetic testing based on next-generation sequencing technology.

Comparative effectiveness review: prostate cancer antigen 3 testing for the diagnosis and management of prostate cancer

PURPOSE

We compared the effectiveness of PCA3 (prostate cancer antigen 3) and select comparators for improving initial or repeat biopsy decision making in men at risk for prostate cancer, or treatment choices in men with prostate cancer.

MATERIALS AND METHODS

MEDLINE®, EMBASE®, Cochrane Database and gray literature were searched from January 1990 through May 2012. Included studies were matched, and measured PCA3 and comparator(s) within a cohort. No matched analyses were possible. Differences in independent performance estimates between PCA3 and comparators were computed within studies. Studies were assessed for quality using QUADAS (Quality Assessment of Diagnostic Accuracy Studies) and for strength of evidence using GRADE (Grading of Recommendations Assessment, Development and Evaluation) criteria.

RESULTS

Among 1,556 publications identified, 34 observational studies were analyzed (24 addressed diagnostic accuracy and 13 addressed treatment decisions). Most studies were conducted in opportunistic cohorts of men referred for procedures and were not designed to answer key questions. Two study biases (partial verification and sampling) were addressed by analyses, allowing some conclusions to be drawn. PCA3 was more discriminatory than total prostate specific antigen increases (eg at an observed 50% specificity, summary sensitivities were 77% and 57%, respectively). Analyses indicated that this finding holds for initial and repeat biopsies, and that the markers were independent predictors. For all other biopsy decision making comparisons and associated health outcomes, strength of evidence was insufficient. For treatment decision making, strength of evidence was insufficient for all outcomes and comparators.

CONCLUSIONS

PCA3 had a higher diagnostic accuracy than total prostate specific antigen increases, but strength of evidence was low (limited confidence in effect estimates). Strength of evidence was insufficient to conclude that PCA3 testing leads to improved health outcomes. For all other outcomes and comparators, strength of evidence was insufficient.

High-throughput massively parallel sequencing for fetal aneuploidy detection from maternal plasma

BACKGROUND

Circulating cell-free (ccf) fetal DNA comprises 3-20% of all the cell-free DNA present in maternal plasma. Numerous research and clinical studies have described the analysis of ccf DNA using next generation sequencing for the detection of fetal aneuploidies with high sensitivity and specificity. We sought to extend the utility of this approach by assessing semi-automated library preparation, higher sample multiplexing during sequencing, and improved bioinformatic tools to enable a higher throughput, more efficient assay while maintaining or improving clinical performance.

METHODS

Whole blood (10mL) was collected from pregnant female donors and plasma separated using centrifugation. Ccf DNA was extracted using column-based methods. Libraries were prepared using an optimized semi-automated library preparation method and sequenced on an Illumina HiSeq2000 sequencer in a 12-plex format. Z-scores were calculated for affected chromosomes using a robust method after normalization and genomic segment filtering. Classification was based upon a standard normal transformed cutoff value of z = 3 for chromosome 21 and z = 3.95 for chromosomes 18 and 13.

RESULTS

Two parallel assay development studies using a total of more than 1900 ccf DNA samples were performed to evaluate the technical feasibility of automating library preparation and increasing the sample multiplexing level. These processes were subsequently combined and a study of 1587 samples was completed to verify the stability of the process-optimized assay. Finally, an unblinded clinical evaluation of 1269 euploid and aneuploid samples utilizing this high-throughput assay coupled to improved bioinformatic procedures was performed. We were able to correctly detect all aneuploid cases with extremely low false positive rates of 0.09%, <0.01%, and 0.08% for trisomies 21, 18, and 13, respectively.

CONCLUSIONS

These data suggest that the developed laboratory methods in concert with improved bioinformatic approaches enable higher sample throughput while maintaining high classification accuracy.

Maternal Body Mass Index during Pregnancy and Offspring Neurocognitive Development

BACKGROUND

This hypothesis generating study explores second trimester maternal body mass index (BMI) during pregnancy and offspring neurocognitive development.

METHODS

Mothers and offspring served as controls in two earlier studies: 101 children at age two years and 118 children at age eight years.

RESULTS

Frequency of maternal BMI ≥30 kg/m² increased from 10% in 1987-1990 to 30% in 2004-2006 (P < 0.001); the socioeconomic gradient became more pronounced. At age two, one or more BSID-III (Bayley Scales of Infant Development, 3rd Edition) scores <85 were more frequent with higher maternal BMI (P = 0.029); regression analysis suggested an inverse relationship between language scores and BMI (P = 0.054). Among eight-year-olds, one or more WISC-III (Wechsler Intelligence Scale for Children, 3rd edition) scores <85 increased with maternal BMI (P = 0.017); regression analysis showed an inverse relationship between performance subscale IQ score and BMI (P = 0.023).

CONCLUSION

Second trimester maternal obesity may be an independent risk factor for some aspects of children's neurocognitive development. Further study is indicated.

Impact of adjusting for the reciprocal relationship between maternal weight and free thyroxine during early pregnancy

BACKGROUND

Among euthyroid pregnant women in a large clinical trial, free thyroxine (FT4) measurements below the 2.5th centile were associated with a 17 lb higher weight (2.9 kg/m(2)) than in the overall study population. We explore this relationship further.

METHODS

Among 9351 women with second trimester thyrotropin (TSH) measurements between 1st and 98th centiles, we examine: (i) the weight/FT4 relationship; (ii) percentages of women in three weight categories at each FT4 decile; (iii) FT4 concentrations in three weight categories at each TSH decile; and (iv) impact of adjusting FT4 for weight--in the reference group and in 190 additional women with elevated TSH measurements.

RESULTS

FT4 values decrease steadily as weight increases (p<0.0001 by ANOVA) among women in the reference group (TSH 0.05-3.8 IU/L). TSH follows no consistent pattern with weight. When stratified into weight tertiles, 48% of women at the lowest FT4 decile are heavy; the percentage decreases steadily to 22% at the highest FT4 decile. Median FT4 is lowest in heaviest women regardless of the TSH level. In the reference group, weight adjustment reduces overall variance by 2.9%. Fewer FT4 measurements are at either extreme (below the 5th FT4 centile: 4.8% before adjustment, 4.7% after adjustment; above the 95th FT4 centile: 5.0% and 4.7%, respectively). Adjustment places more light weight women and fewer heavy women below the 5th FT4 centile; the converse above the 95th centile. Between TSH 3.8 and 5 IU/L, the FT4 percentage below the 5th FT4 centile is not elevated (3.8% before adjustment, 3.1% after adjustment). Percentage of FT4 values above the 95th centile, however, is lower (1.5% before adjustment, 0.8% after adjustment). Above TSH 5 IU/L, 25% of women have FT4 values below the 5th FT4 centile; weight adjustment raises this to 30%; no FT4 values remain above the 95th FT4 centile.

CONCLUSIONS

During early pregnancy, TSH values are not associated with weight, unlike nonpregnant adults. Lower average FT4 values among heavy women at all TSH deciles partially explain interindividual differences in FT4 reference ranges. The continuous reciprocal relationship between weight and FT4 explains lower FT4 with higher weight. Weight adjustment refines FT4 interpretation.

Feasibility of Using Plasma Rather Than Serum in First and Second Trimester Multiple Marker Down's Syndrome Screening

Objective

To compare maternal plasma with serum for measuring markers currently used in first and second trimester screening for Down's syndrome.

Setting

A laboratory-based investigation of two sample types in assays used in prenatal screening for Down's syndrome.

Methods

A paired data-set included both plasma and serum from 101 pregnant women. A nested case/control data-set included only plasma samples from 34 first and 23 second trimester Down's syndrome pregnancies, each matched with six euploid controls. Analyte levels were measured and converted to multiples of the median (MoM).

Results

In the paired data-set, each of the five analytes (alphafetoprotein, unconjugated estriol, human chorionic gonadotropin, inhibin-A and pregnancy-associated plasma protein A) in serum and plasma was highly correlated (r > 0.970) and after conversion to MoM, the resulting distributions were equivalent ( P > 0.7). In the matched data-set, plasma-based median MoM levels in cases were consistent with the published serum counterparts for all markers.

Conclusions

This study provides strong evidence that current serum-based prenatal screening can be performed equally well using plasma samples. This may prove useful, especially if secondary screening using a DNA-based test requires maternal plasma.

Mid-gestational maternal free thyroxine concentration and offspring neurocognitive development at age two years

CONTEXT

Lower neurocognitive development scores at age 2 yr have been reported in association with euthyroid hypothyroxinemia during early pregnancy.

OBJECTIVE

The objective of this study was to further explore this association with euthyroid hypothyroxinemia during early pregnancy.

DESIGN

This was an observational, nested case-control study.

SETTING

The study was conducted at physician offices and prenatal clinics throughout Maine.

STUDY SUBJECTS

Between May 2004 and March 2006, TSH was measured in 5734 women in conjunction with second-trimester Down syndrome screening. After completion of pregnancy, free T(4) was measured in stored second-trimester sera from euthyroid women (TSH 0.1-3.5 mIU/ml; n = 5560). Women with free T(4) at the third centile or less (n = 99) were matched with women whose free T(4) was at the 10th to the 90th centile (n = 99).

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURE

Bayley Scales of Infant Development (BSID III) were administered to the 198 offspring at age 2 yr. Scores for cognitive, language, and motor development were compared between matched pairs of offspring from the two groups before and after correcting for relevant variables.

RESULTS

Unadjusted BSID-III scores (cognitive, language, and motor) were lower by about 3% at age 2 yr among offspring of 98 hypothyroxinemic women (cases), reaching borderline significance for cognitive and motor scores. After adjustment for gestational age, the child's age at testing, maternal weight, and education, all differences diminished and became nonsignificant. Scores less than 85 were more frequent among case children but did not reach statistical significance (P = 0.14).

CONCLUSIONS

Isolated hypothyroxinemia during the second trimester is not associated with significantly lower BSID-III scores at age 2 yr, compared with scores for offspring of matched euthyroxinemic women.

The relationship between PTH and 25-hydroxy vitamin D early in pregnancy

OBJECTIVE

Measure serum PTH and 25(OH)D in a cross-sectional sample of pregnant women at 11th through 13th weeks' gestation to examine vitamin D status and consider implications.

DESIGN

Observational: we retrieved residual sera stored at -20 °C after routine first trimester Down's syndrome screening, distributed over 12 months.

PATIENTS

430 African American women and 586 Caucasian women.

MEASUREMENTS

PTH and 25-hydroxy vitamin D [25(OH)D] immunoassays.

RESULTS

PTH medians were: 1·33 pmol/l (African American women); 1·20 pmol/l (Caucasian women) (t = 0·43, P = 0·7). Concentrations were highest in winter and decreased significantly in spring, fall, and summer. There was a direct PTH/weight relationship in Caucasian (t = 3·12, P < 0·002), but not African American women (t = 1·34, P = 0·18). Median 25(OH)D concentrations were 47·5 nmol/l (African American women) and 65 nmol/l (Caucasian women) (t = 13·7, P < 0·001). Concentrations were lowest in winter and rose significantly in spring, fall, and summer. Reciprocal 25(OH)D/weight relationships existed for both racial groups (t =-4·31 P < 0·001; t = 4·54, P < 0·001, respectively). Among 68 Caucasian women who smoked, median PTH and 25(OH)D concentrations were somewhat lower (P = ns). In separate regression models with PTH and 25(OH)D [dependent variables] and season, weight and smoking [independent variables], the only qualifying interactive term was in the Caucasian PTH model (season*1/weight). A regression model applied to adjusted scatter plots of PTH vs 25(OH)D indicated a weak relationship.

CONCLUSIONS

The PTH/25(OH)D relationship is weaker during early pregnancy than in non-pregnant adults, making it unreliable for estimating vitamin D sufficiency. A suitable reference point for sufficiency might be the maternal 25(OH)D level considered sufficient for adequate transfer to neonates.

Noninvasive fetal sex determination using cell-free fetal DNA: a systematic review and meta-analysis

CONTEXT

Noninvasive prenatal determination of fetal sex using cell-free fetal DNA provides an alternative to invasive techniques for some heritable disorders. In some countries this testing has transitioned to clinical care, despite the absence of a formal assessment of performance.

OBJECTIVE

To document overall test performance of noninvasive fetal sex determination using cell-free fetal DNA and to identify variables that affect performance.

DATA SOURCES

Systematic review and meta-analysis with search of PubMed (January 1, 1997-April 17, 2011) to identify English-language human studies reporting primary data. References from review articles were also searched.

STUDY SELECTION AND DATA EXTRACTION

Abstracts were read independently to identify studies reporting primary data suitable for analysis. Covariates included publication year, sample type, DNA amplification methodology, Y chromosome sequence, and gestational age. Data were independently extracted by 2 reviewers.

RESULTS

From 57 selected studies, 80 data sets (representing 3524 male-bearing pregnancies and 3017 female-bearing pregnancies) were analyzed. Overall performance of the test to detect Y chromosome sequences had the following characteristics: sensitivity, 95.4% (95% confidence interval [CI], 94.7%-96.1%) and specificity, 98.6% (95% CI, 98.1%-99.0%); diagnostic odds ratio (OR), 885; positive predictive value, 98.8%; negative predictive value, 94.8%; area under curve (AUC), 0.993 (95% CI, 0.989-0.995), with significant interstudy heterogeneity. DNA methodology and gestational age had the largest effects on test performance. Methodology test characteristics were AUC, 0.988 (95% CI, 0.979-0.993) for polymerase chain reaction (PCR) and AUC, 0.996 (95% CI, 0.993-0.998) for real-time quantitative PCR (RTQ-PCR) (P = .02). Gestational age test characteristics were AUC, 0.989 (95% CI, 0.965-0.998) (<7 weeks); AUC, 0.994 (95% CI, 0.987-0.997) (7-12 weeks); AUC, 0.992 (95% CI, 0.983-0.996) (13-20 weeks); and AUC, 0.998 (95% CI, 0.990-0.999) (>20 weeks) (P = .02 for comparison of diagnostic ORs across age ranges). RTQ-PCR (sensitivity, 96.0%; specificity, 99.0%) outperformed conventional PCR (sensitivity, 94.0%; specificity, 97.3%). Testing after 20 weeks (sensitivity, 99.0%; specificity, 99.6%) outperformed testing prior to 7 weeks (sensitivity, 74.5%; specificity, 99.1%), testing at 7 through 12 weeks (sensitivity, 94.8%; specificity, 98.9%), and 13 through 20 weeks (sensitivity, 95.5%; specificity, 99.1%).

CONCLUSIONS

Despite interstudy variability, performance was high using maternal blood. Sensitivity and specificity for detection of Y chromosome sequences was greatest using RTQ-PCR after 20 weeks' gestation. Tests using urine and tests performed before 7 weeks' gestation were unreliable.

Prevalence of steroid sulfatase deficiency in California according to race and ethnicity

OBJECTIVE

Estimate steroid sulfatase deficiency (STSD) prevalence among California's racial/ethnic groups using data from a previous study focused on prenatal detection of Smith-Lemli-Opitz syndrome (SLOS). SLOS and STSD both have low maternal serum unconjugated estriol (uE3) levels.

METHODS

Prevalence was estimated using three steps: listing clinically identified cases; modeling STSD frequency at three uE3 intervals using diagnostic urine steroid measurements; applying this model to determine frequency in pregnancies not providing urine.

RESULTS

Overall, 2151 of 777 088 pregnancies (0.28%) were screen positive; 1379 of these were explained and excluded. Fifty-four cases were diagnosed clinically among 707 remaining pregnancies with a male fetus. Urine steroid testing identified 74 additional STSD cases: 66 (89.2%) at uE3 values < 0.15 MoM, 8 (10.8%) at 0.15-0.20 MoM, and 0 (0%) at > 0.20 MoM. Modeling estimated 107.5 STSD cases among 370 pregnancies without urine samples. In males, STSD prevalence was highest among non-Hispanic Whites (1:1230) compared to Hispanics (1:1620) and Asians (1:1790), but differences were not significant. No STSD pregnancies were found among 65 screen positive Black women.

CONCLUSION

The overall prevalence estimate of 1:1500 males is consistent with published estimates and is reasonable for counseling, except among Black pregnancies where no reliable estimate could be made.

Four years' experience with an interlaboratory comparison program involving first-trimester markers of Down syndrome

CONTEXT

We initiated a voluntary, self-funded interlaboratory comparison program in the fall of 2005 because no proficiency testing program was available to laboratories in North America offering first-trimester, combined serum and ultrasound, Down syndrome screening. Objectives.-To evaluate the first 4 years of the interlaboratory comparison program against stated goals, to identify areas of concern, and to create new initiatives as indicated.

DESIGN

Five serum samples are distributed 3 times a year to be tested for pregnancy-associated plasma protein A, human chorionic gonadotropin or its β subunit, and dimeric inhibin-A; participants convert these results into multiples of the median. Patient histories include nuchal translucency information that enables the calculation of the risk of Down syndrome. Also included are educational components linked to interlaboratory comparison program results. Assessment of integrated (first- and second-trimester markers) risks is accomplished by having participants combine interlaboratory comparison program results with their results from a second-trimester proficiency testing program administered by the College of American Pathologists.

RESULTS

The precision profile for pregnancy-associated plasma protein A shows decreasing coefficients of variation with increasing pregnancy-associated plasma protein A concentrations and multiples of the median (25% to 11% and 30% to 15%, respectively). In contrast, coefficients of variation are a relatively constant 12% throughout the entire range of human chorionic gonadotropin results. On a logarithmic scale, the median coefficient of variation of the risk of Down syndrome is 9%.

CONCLUSIONS

Participants in the interlaboratory comparison program reliably measure analytes, compute multiples of the median, and calculate consistent Down syndrome risks. Assays for the measurement of pregnancy-associated plasma protein A are not standardized and are less precise than those for human chorionic gonadotropin. Participants calculate reliable median equations given sonographer-specific sets of paired crown-rump length and nuchal translucency measurements.

Examination of the pregnancy-associated plasma protein-A assay on the Beckman Coulter Access® platform: suitability for use in first trimester Down's syndrome screening

Objective

To explore the clinical validity of the new Access® pregnancy-associated plasma protein-A (PAPP-A) assay for Down's syndrome screening.

Setting

Academic hospital.

Method

Residual serum samples ( n = 416) received for routine first trimester Down's syndrome screening (10-13 weeks) were retrieved from freezer storage and tested using two PAPP-A immunoassay methods. The new Access® assay was specifically compared, on a subset of these samples ( n = 194), with an assay proven to give acceptable Down's syndrome screening performance, the PerkinElmer (PE) AutoDELFIA method. Access® PAPP-A levels were examined in relation to gestational age and maternal weight, and were compared with the PE method by regression and Bland-Altman analyses.

Results

Access® PAPP-A assay results were highly correlated with the PE AutoDELFIA method ( r = 0.97). PAPP-A levels obtained using the Access® assay increased with advancing gestational age and were inversely related to maternal weight, as expected. The distribution of multiples of the median (MoM) values fit a log Gaussian distribution and the standard deviation of the log MoM (0.2331) matched published estimates. PAPP-A MoM levels in Down's syndrome pregnancies ( n = 6, median 0.30) showed the expected reduction.

Conclusion

Using an appropriate gestational age-specific median equation, the Access® PAPP-A assay is expected to perform acceptably in first trimester Down's syndrome screening.

Second and first trimester estimation of risk for Down syndrome: implementation and performance in the SAFER study

OBJECTIVES

Document patient choices and screening performance (false positive and detection rates) when three improved Down syndrome screening protocols were introduced coincidentally.

METHOD

Second-trimester 'triple marker' screening was expanded by adding second-trimester dimeric inhibin-A (four-marker), with or without first-trimester pregnancy-associated plasma protein-A (five-marker). Nuchal translucency (NT) measurements were included when available from accredited sonographers (six-marker). For assigning risk, two sets of marker distribution parameters were evaluated.

RESULTS

Over 3.5 years, 8571 women enrolled (median age 30.6 years). Uptake of the four-, five- and six-marker protocols was 18%, 46% and 36%, respectively. Of those selecting an integrated test (five or six markers), 9.7% did not provide the second trimester serum sample. False positive rates decreased with added markers (5.2%, 5.1% and 2.5%, respectively) and varied between the two parameter sets, while detection remained high. Overall, 21 of 23 cases were detected (91%, 95% CI 73-98%) at a 4.2% false positive rate (95% CI 3.3-5.1%).

CONCLUSIONS

Integrated screening protocols were chosen 4.6 times more often than four-marker screening (82% vs. 18% uptake). Overall detection was higher and false positives lower, consistent with recent guidelines. Important performance factors include gestational dating method, risk cut-off, and the parameter set used to assign risk.