False-positive results in neonatal screening for cystic fibrosis based on a three-stage protocol (IRT/DNA/IRT): Should we adjust IRT cut-off to ethnic origin?

Cystic Fibrosis Newborn Screening: A Systematic Review-Driven Consensus Guideline from the United States Cystic Fibrosis Foundation

Newborn screening for cystic fibrosis (CF) has been universal in the US since 2010; however, there is significant variation among newborn screening algorithms. Systematic reviews were used to develop seven recommendations for newborn screening program practices to improve timeliness, sensitivity, and equity in diagnosing infants with CF: (1) The CF Foundation recommends the use of a floating immunoreactive trypsinogen (IRT) cutoff over a fixed IRT cutoff; (2) The CF Foundation recommends using a very high IRT referral strategy in CF newborn screening programs whose variant panel does not include all CF-causing variants in CFTR2 or does not have a variant panel that achieves at least 95% sensitivity in all ancestral groups within the state; (3) The CF Foundation recommends that CF newborn screening algorithms should not limit CFTR variant detection to the F508del variant or variants included in the American College of Medical Genetics-23 panel; (4) The CF Foundation recommends that CF newborn screening programs screen for all CF-causing CFTR variants in CFTR2; (5) The CF Foundation recommends conducting CFTR variant screening twice weekly or more frequently as resources allow; (6) The CF Foundation recommends the inclusion of a CFTR sequencing tier following IRT and CFTR variant panel testing to improve the specificity and positive predictive value of CF newborn screening; (7) The CF Foundation recommends that both the primary care provider and the CF specialist be notified of abnormal newborn screening results. Through implementation, it is anticipated that these recommendations will result in improved sensitivity, equity, and timeliness of CF newborn screening, leading to improved health outcomes for all individuals diagnosed with CF following newborn screening and a decreased burden on families.

Metabolic diversity in human populations and correlation with genetic and ancestral geographic distances

DNA polymorphic markers and self-defined ethnicity groupings are used to group individuals with shared ancient geographic ancestry. Here we studied whether ancestral relationships between individuals could be identified from metabolic screening data reported by the California newborn screening (NBS) program. NBS data includes 41 blood metabolites measured by tandem mass spectrometry from singleton babies in 17 parent-reported ethnicity groupings. Ethnicity-associated differences identified for 71% of NBS metabolites (29 of 41, Cohen's d > 0.5) showed larger differences in blood levels of acylcarnitines than of amino acids (P < 1e-4). A metabolic distance measure, developed to compare ethnic groupings based on metabolic differences, showed low positive correlation with genetic and ancient geographic distances between the groups' ancestral world populations. Several outlier group pairs were identified with larger genetic and smaller metabolic distances (Black versus White) or with smaller genetic and larger metabolic distances (Chinese versus Japanese) indicating the influence of genetic and of environmental factors on metabolism. Using machine learning, comparison of metabolic profiles between all pairs of ethnic groupings distinguished individuals with larger genetic distance (Black versus Chinese, AUC = 0.96), while genetically more similar individuals could not be separated metabolically (Hispanic versus Native American, AUC = 0.51). Additionally, we identified metabolites informative for inferring metabolic ancestry in individuals from genetically similar populations, which included biomarkers for inborn metabolic disorders (C10:1, C12:1, C3, C5OH, Leucine-Isoleucine). This work sheds new light on metabolic differences in healthy newborns in diverse populations, which could have implications for improving genetic disease screening.

Ethnic variability in newborn metabolic screening markers associated with false-positive outcomes

Newborn screening (NBS) programmes utilise information on a variety of clinical variables such as gestational age, sex, and birth weight to reduce false-positive screens for inborn metabolic disorders. Here we study the influence of ethnicity on metabolic marker levels in a diverse newborn population. NBS data from screen-negative singleton babies (n = 100 000) were analysed, which included blood metabolic markers measured by tandem mass spectrometry and ethnicity status reported by the parents. Metabolic marker levels were compared between major ethnic groups (Asian, Black, Hispanic, White) using effect size analysis, which controlled for group size differences and influence from clinical variables. Marker level differences found between ethnic groups were correlated to NBS data from 2532 false-positive cases for four metabolic diseases: glutaric acidemia type 1 (GA-1), methylmalonic acidemia (MMA), ornithine transcarbamylase deficiency (OTCD), and very long-chain acyl-CoA dehydrogenase deficiency (VLCADD). In the result, 79% of the metabolic markers (34 of 43) had ethnicity-related differences. Compared to the other groups, Black infants had elevated GA-1 markers (C5DC, Cohen's d = .37, P < .001), Hispanics had elevated MMA markers (C3, Cohen's d = .13, P < .001, and C3/C2, Cohen's d = .27, P < .001); and Whites had elevated VLCADD markers (C14, Cohen's d = .28, P < .001, and C14:1, Cohen's d = .22, P < .001) and decreased OTCD markers (citrulline, Cohen's d = -.26, P < .001). These findings correlated with the higher false-positive rates in Black infants for GA-1, in Hispanics for MMA, and in Whites for OTCD and for VLCADD. Web-based tools are available to analyse ethnicity-related changes in newborn metabolism and to support developing methods to identify false-positives in metabolic screening.

Utility of a very high IRT/No mutation referral category in cystic fibrosis newborn screening

Newborn screening for Cystic Fibrosis (CF) began in New York in October, 2002 using immunoreactive trypsinogen (IRT)/DNA methodology. Infants with at least one CFTR mutation or very high IRT and no mutations (VHIRT) are referred for sweat testing. In a preliminary analysis, we noted a very low positive predictive value (PPV) and preponderance of Hispanic infants in the group of infants with CF referred for VHIRT, which led to a decision to revise, but not eliminate, the VHIRT category. Automatic referral for specimens with VHIRT collected on the day of birth was eliminated, and the VHIRT threshold was raised from 0.2% to 0.1%. In this report, we describe outcomes from VHIRT referrals among 2.4 million infants screened between March 2003 and February 2013. Following the algorithm change, referrals decreased by 37.8% overall (annual mean 1,485 vs. 923), and the VHIRT PPV improved (0.6-1.0%). The number of infants diagnosed has remained consistent at 1 in 4,400 births. The proportion of Black/Hispanic/Asian/Other infants with confirmed CF, CFTR-related metabolic syndrome (CRMS), or possible CF/CRMS was 21.3% in infants with 1-2 mutations, but 75.8% in the VHIRT group. In conclusion, although the PPV among VHIRT referrals remains low, had this category never been implemented, 24 infants with confirmed CF, and 9 infants with CRMS or possible CF/CRMS, most of whom were Hispanic, would have been missed over the 10 years. Information from this study may be helpful in assessing the need for the VHIRT category and algorithm changes in other screening programs.

Differences in immunoreactive trypsin values between type of feeding and ethnicity in neonatal cystic fibrosis screening: a cross-sectional study

BACKGROUND

We studied the differences in immunoreactive trypsin (IRT) in neonatal screening for cystic fibrosis (CF) associated individually with the age of the newborn, ethnicity and environmental temperature. In this study, we determine the overall influence of environmental temperature at birth, gender, feeding, gestational age, maternal age and ethnic origin on an abnormal IRT result.

METHODS

Cross-sectional observational study. A sample was selected of newborns from Alicante (Spain) who underwent neonatal CF screening in 2012-2013. Primary variable: abnormal IRT levels (≥65 ng/ml). Secondary variables: gender, maternal origin, maternal age (years) (<20, 20-40, >40), gestational age (weeks) (<32, 32-37, >37), type of feeding (natural, formula, mixed and special nutrition), >20 days from birth to blood collection, and average temperature during the month of birth (in°C). Using a multivariate logistic regression model the adjusted odds ratios (ORs) were estimated to analyze the association between atypical IRT levels and the study variables. The α error was 5% and confidence intervals (CI) were calculated for the most relevant parameters.

RESULTS

Of a total of 13,310 samples, 199 were abnormal (1.34%). Significant associated factors: feeding method (natural → OR = 1; mixed → OR = 0.53, 95% CI: 0.31-0.89; formula → OR = 0.72, 95% CI: 0.48-1.07; special → OR = 21.88, 95% CI: 6.92-69.14; p < 0.001).

CONCLUSIONS

Newborns receiving special nutrition have a 20-fold higher risk for abnormal IRT levels, and screening is advisable once normalized feeding is initiated. It is advisable to consider ethnic variability. Seasonality was not important.

Closing the gaps in pediatric laboratory reference intervals: a CALIPER database of 40 biochemical markers in a healthy and multiethnic population of children

BACKGROUND

Pediatric healthcare is critically dependent on the availability of accurate and precise laboratory biomarkers of pediatric disease, and on the availability of reference intervals to allow appropriate clinical interpretation. The development and growth of children profoundly influence normal circulating concentrations of biochemical markers and thus the respective reference intervals. There are currently substantial gaps in our knowledge of the influences of age, sex, and ethnicity on reference intervals. We report a comprehensive covariate-stratified reference interval database established from a healthy, nonhospitalized, and multiethnic pediatric population.

METHODS

Healthy children and adolescents (n = 2188, newborn to 18 years of age) were recruited from a multiethnic population with informed parental consent and were assessed from completed questionnaires and according to defined exclusion criteria. Whole-blood samples were collected for establishing age- and sex-stratified reference intervals for 40 serum biochemical markers (serum chemistry, enzymes, lipids, proteins) on the Abbott ARCHITECT c8000 analyzer.

RESULTS

Reference intervals were generated according to CLSI C28-A3 statistical guidelines. Caucasians, East Asians, and South Asian participants were evaluated with respect to the influence of ethnicity, and statistically significant differences were observed for 7 specific biomarkers.

CONCLUSIONS

The establishment of a new comprehensive database of pediatric reference intervals is part of the Canadian Laboratory Initiative in Pediatric Reference Intervals (CALIPER). It should assist laboratorians and pediatricians in interpreting test results more accurately and thereby lead to improved diagnosis of childhood diseases and reduced patient risk. The database will also be of global benefit once reference intervals are validated in transference studies with other analytical platforms and local populations, as recommended by the CLSI.

Variation in immunoreactive trypsinogen concentrations among Michigan newborns and implications for cystic fibrosis newborn screening

OBJECTIVE

To investigate variation in immunoreactive trypsinogen (IRT) concentrations by race, sex, birth weight, and gestational age and their implications for the use of percentile-based cutoffs for cystic fibrosis (CF) newborn screening (NBS) programs.

PATIENTS AND METHODS

This cross-sectional population-based study of resident infants screened in Michigan investigates associations between demographic and perinatal variables and IRT concentrations after controlling for covariates. This study also analyzed how 96th and 99.8th IRT concentration percentiles values calculated by Michigan NBS vary by demographic and perinatal factors. Characteristics of infants having high (≥99.8th percentile) IRT concentrations and negative DNA tests are also explored.

RESULTS

IRT mean concentrations and percentiles vary significantly by race, birth weight, gestational age, and to a lesser degree by sex. The greatest variation in mean IRT concentrations was observed among racial categories; black infants had an adjusted mean concentration of 36 ng/ml and Asian/Pacific Islander infants had a mean concentration of 25 ng/ml compared to an average concentration of 28 ng/ml in white infants and infants of other races.

CONCLUSIONS

Variation in IRT concentrations resulted in the over-representation of certain groups referred for secondary testing, particularly referrals for sweat testing based on very high (≥99.8th percentile) concentrations alone, which is no longer recommended in Michigan. Further research may be warranted to evaluate initial IRT cutoffs used for CF NBS.

Implementation of the French nationwide cystic fibrosis newborn screening program

OBJECTIVES

To describe optimization of a nationwide newborn screening program for cystic fibrosis (CF) that combines an immunoreactive trypsinogen (IRT) assay and DNA mutation analysis in dried blood samples at day 3.

STUDY DESIGN

Data from regional screening laboratories and CF care centers were centralized and periodically analyzed to allow adaptation, thus limiting the number of false-positive cases.

RESULTS

A total of 2717905 infants were screened between 2002 and 2005. Flow chart protocol was modified twice. First, the IRT d3 cutoff value increased from 60 to 65 microg/L, thus decreasing the percentage of samples requiring mutation analysis from 0.82% to 0.64%. Second, for infants with no mutations using the screening panel, a recall for IRT was performed only if IRT d3 was > 100 microg/L; the percentage of recalls decreased from 0.51% to 0.12%, and the percentage of infants requiring a sweat test decreased from 0.14% to 0.01%. No significant change in the CF detection rate was observed after these 2 modifications. A total of 625 CF cases were detected, and 22 false-negative findings (3.4%) were observed, most of them inevitable, with a low initial IRT.

CONCLUSIONS

The centralized data analysis led to changes in the screening strategy to optimise the newborn screening program.

Elevated IRT levels in African-American infants: implications for newborn screening in an ethnically diverse population

During the first 4 years of newborn screening (NBS) for Cystic Fibrosis (CF) in New York there was a statistically significant, twofold greater relative risk of an Immunoreactive Trypsinogen (IRT) level greater than 95% in African-American infants. The reason for this previously reported increase in IRT level in African-American infants is unclear. The positive predictive value of a screen positive result in this population was only 0.3%. The bulk of screen-positive African-American infants were in the top 0.2% (IRT) group, with no CF mutations isolated. Repeat IRT testing at 2-3 weeks of age may represent a suitable approach to decrease the false-positive rate in this population.