BACKGROUND:Respiratory syncytial virus (RSV) is the leading cause of respiratory infection in young children. Although passive immunization strategies are available for infants, the relationship between population immunity and epidemic intensity remains poorly understood. Measuring maternally derived RSV antibodies in newborns could provide a scalable sentinel approach to monitor population immunity. OBJECTIVE:To demonstrate the feasibility of using residual newborn dried blood spots (NDBS), collected universally, to quantify population-level RSV antibody immunity at birth. METHODS:We developed a method to quantify RSV antibody levels and function using residual NDBS from the British Columbia Newborn Screening Program. Assay performance and stability were first evaluated using adult dried blood spot (DBS) and serum controls, then applied to two NDBS sets. RESULTS:In adult DBS, IgG against RSV pre-fusion (pre-F) protein was stable for at least 30 days and ⁓20-fold lower than corresponding sera. In NDBS, pre-F IgG levels remained stable for 140 days at room temperature, correlated with viral neutralization titers (ρ=0.64, p < 0.0001; N = 159), and showed antigen specificity through competitive blocking with soluble post-F protein across multiple RSV antigens (pre-F, post-F, N, Ga, Gb). ⁓42% of samples were below the lower limit of quantification. CONCLUSIONS:RSV antibody immunity can be quantified from residual NDBS. This scalable approach enables population-level surveillance of RSV immunity and supports large-scale studies of seasonal RSV epidemiology and correlates of protection across regions.

BackgroundSevere combined immunodeficiency (SCID) is a life-threatening condition that requires urgent medical attention. Newborn screening (NBS) using the T cell receptor excision circle (TREC) assay facilitates early diagnosis of SCID, which is crucial for improving outcomes.ObjectivesDescribe the diagnoses and outcomes of the first 2.5 years of NBS for SCID in British Columbia and the Yukon, Canada.MethodsAn interdisciplinary working group of health professionals met at regular intervals prior to and after implementing NBS for SCID. We developed an algorithm for the evaluation and initial management of infants with an abnormal NBS for SCID based on a literature review and local expert consensus. The diagnoses and outcomes of infants with a positive NBS were monitored prospectively. TRECs were measured from dried blood spots of newborns, with the threshold for an abnormal NBS determined using multiples of the median to achieve a positivity rate of 0.1%. Absolute T cell counts less than 1,500 cells/mcL or naïve CD4 or CD8 T cell percentages less than 50% were considered abnormal and prompted immunology consultation.Results and DiscussionA total of 110,156 infants were screened between October 2022 and April 2025. There were 2 infants diagnosed with SCID, resulting in a population-based incidence of 1 in 55,078. Both underwent stem cell transplantation within 4 months of life and had no infections at the time of transplant. There was one case of congenital athymia secondary to 22q11 microdeletion syndrome identified by NBS for SCID, who underwent a successful thymic transplantation at 5 months of age. There were no cases of SCID diagnosed outside of the NBS program within this time frame.ConclusionOur experience supports the value of NBS using the TREC assay in facilitating early diagnosis and treatment of infants with SCID.

Gamma-butyrobetaine hydroxylase (BBOX1) catalyses the last step of carnitine biosynthesis, converting γ-butyrobetaine (γ-BB) into L-carnitine. Here we show, for the first time, that biallelic variants in BBOX1 are associated with decreased levels of L-carnitine and increased plasma levels of γ-BB in three patients from two unrelated families presenting with myopathic, neurodevelopmental, and late-onset psychiatric manifestations. Using a knockout C. elegans model of BBOX1 homolog, gbh-1, and strains harboring patient-derived variants (gbh-1(D72G) for p.Asp59Gly, gbh-1(G283R) for p.Gly263Arg, and gbh-1(G247Vfs6) for p.Gly227Valfs*6), we show very low L-carnitine levels and significantly elevated γ-BB in c.675delA and c.787G>A mutants, and moderately elevated γ-BB in c.176A>G. Furthermore, we observed a lethal embryonic phenotype for the gbh-1 loss-of-function strains, which was rescued upon L-carnitine supplementation. Our study provides novel insights into the clinical and biochemical consequences of BBOX1-related L-carnitine biosynthesis deficiency and establishes C. elegans as a model to study the effects of BBOX1 deficiency.

Purpose:Newborn screening for 21-hydroxylase deficiency congenital adrenal hyperplasia (CAH) has a high false-positive rate. A second-tier steroid profile using liquid chromatography mass spectrometry can improve specificity. Multiple screening algorithms were evaluated to optimize the performance of screening for salt-wasting CAH (SW-CAH). Methods:Principal components analysis guided potential combinations of steroid biomarkers for evaluation in a study population of 1710 immunoassay-positive samples proceeding to the second-tier steroid profile in the Newborn Screening Ontario program between August 2020 and April 2023. A Monte Carlo simulation was used to evaluate the performance of algorithms and cutoffs. Results:Optimal performance for the identification of SW-CAH used a 3-component second-tier algorithm: detectable 21-deoxycortisol (≥ 2.1 nmol/L); 17-hydroxyprogesterone + 21-deoxycortisol ≥ 40 nmol/L; and ratio of (17-hydroxyprogesterone + 21-deoxycortisol)/cortisol ≥ 0.3. All 8 cases of SW-CAH were accurately identified with a positive predictive value of 70% and 100% sensitivity for SW-CAH, whereas 1 known case of simple virilizing (SV) CAH screened negative. When applied to 26 historical cases, the algorithm identified all 13 cases of SW-CAH and all 6 SV-CAH cases, whereas other forms of CAH were filtered out because of low 21-deoxycortisol. Conclusion:Using 21-deoxycortisol for second-tier screening and applying a 3-component algorithm can improve performance of newborn screening for SW-CAH, reducing burden on patients and the health care system. Although cases of SV-CAH may be identified, the thresholds were set to identify life-threatening SW-CAH with a high positive predictive value and 100% sensitivity.

Abstract Background Severe Combined Immunodeficiency (SCID) is an inborn error of immunity characterized by severely low T cell levels and function. Early diagnosis is essential to prevent serious infections and improve outcomes. Newborn screening (NBS) for SCID provides a way to detect SCID and other conditions associated with T cell lymphopenia in the neonatal period. Objectives 1) Optimize the implementation of a NBS program for SCID in British Columbia (BC), Canada; and 2) create a systematic method for monitoring the diagnoses and outcomes of infants with a positive screen to facilitate continuous improvement of the NBS program. Design/Methods An interdisciplinary working group comprised of immunologists, biochemical geneticists, and hematopathologists met at regular intervals prior to and after implementing NBS for SCID in BC. We developed an algorithm for the evaluation and initial management of infants with an abnormal NBS for SCID based on literature review and local expert consensus. Using a REDCap database, we tracked the prevalence, evaluation, diagnoses and outcomes of infants with a positive NBS. The database also monitored diagnoses and outcomes of children referred to Immunology outside of the NBS program. Plan-do-study-act cycles included creation of clinical and educational guidelines on SCID, optimization of abnormal NBS cut-off values, and reflex chromosomal microarray (CMA) testing of infants with confirmed T cell lymphopenia. Results Between October 3, 2022 and June 16, 2023, 28,816 initial samples were tested, and 30 infants had a positive screen for SCID. Of the 30 infants, 10 were ultimately diagnosed with conditions associated with T cell lymphopenia. Diagnosis led to avoidance of live viral vaccines and implementation of infection precaution measures. No infants experienced complications related to live viral vaccine administration, compared to 1 case in the preceding 12 months prior to NBS implementation. In February 2023, the threshold for an abnormal NBS was adjusted to achieve the goal positive screen frequency of 0.1%. Performing reflex CMA testing on infants with confirmed T cell lymphopenia led to rapid diagnosis of chromosomal microdeletion syndromes, avoiding unnecessary second tier testing. Since implementing NBS for SCID in BC, there have been no cases of SCID diagnosed outside of the NBS program. Conclusion Establishing an interdisciplinary working group and clinical database facilitated the smooth integration and continuous improvement of NBS for SCID in BC. This model can be applied to other healthcare systems to support teams and ensure the best possible outcomes for affected patients.

We investigate the diagnostic accuracy and predictive value of finger prick capillary dried blood spot (DBS) samples tested by a quantitative multiplex anti-immunoglobulin G (IgG) assay to detect severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies after infection or vaccination. This cross-sectional study involved participants (n = 6,841) from several serological surveys conducted in nonhospitalized children and adults throughout 2020 and 2021 in British Columbia (BC), Canada. Analysis used paired DBS and serum samples from a subset of participants (n = 642) prior to vaccination to establish signal thresholds and calculate diagnostic accuracy by logistic regression. Discrimination of the logistic regression model was assessed by receiver operator curve (ROC) analysis in an n = 2,000 bootstrap of the paired sample (n = 642). The model was cross-validated in a subset of vaccinated persons (n = 90). Unpaired DBS samples (n = 6,723) were used to evaluate anti-IgG signal distributions. In comparison to paired serum, DBS samples from an unvaccinated population possessed a sensitivity of 79% (95% confidence interval [95% CI]: 58 to 91%) and specificity of 97% (95% CI: 95 to 98%). ROC analysis found that DBS samples accurately classify SARS-CoV-2 seroconversion at an 88% percent rate (area under the curve [AUC] = 88% [95% CI: 80 to 95%]). In coronavirus disease 2019 (COVID-19) vaccine dose one or two recipients, the sensitivity of DBS testing increased to 97% (95% CI: 83 to 99%) and 100% (95% CI: 88 to 100%). Modeling found that DBS testing possesses a high positive predictive value (98% [95% CI: 97 to 98%]) in a population with 75% seroprevalence. We demonstrate that DBS testing should be considered to reliably detect SARS-CoV-2 seropositivity from natural infection or vaccination. IMPORTANCE Dried blood spot samples have comparable diagnostic accuracy to serum collected by venipuncture when tested by an electrochemiluminescent assay for antibodies and should be considered to reliably detect seropositivity following SARS-CoV-2 infection and/or vaccination.

Urine organic acids profiling by gas chromatography-mass spectrometry (GC-MS) is routinely performed in hospital biochemical genetics laboratories for the investigation of inborn errors of metabolism. In particular, accurate identification of urinary levels of 3-hydroxyglutaric acid (3-OHGA) is important for diagnosing glutaric aciduria type 1 (GA1), but can be challenging by routine GC-MS profiling analysis due to co-elution and spectral similarity with the isomer 2-hydroxyglutaric acid (2-OHGA). To improve analytical specificity, unique ions were selected and a simple second-tier reinjection method was developed to enhance the chromatographic separation of the 2-and 3-OHGA isomers and potential unknown interferences. Specimens flagging on the routine analysis were simply reinjected on the same GC column using a modified temperature gradient containing an isothermal hold. Correlation between the reinjection and initial methods was higher for 2-OHGA (R = 0.9612) compared to 3-OHGA (R = 0.7242). Mean differences between the reinjection and initial methods for 2-OHGA and 3-OHGA were-8.5% and-61.1% respectively. The large decrease in 3-OHGA concentration for many specimens using the reinjection method was primarily attributable to separation from unknown variable interference(s) that were falsely elevating 3-OHGA in the initial analysis despite the use of a more unique quantifier ion. Overall, the reinjection approach increased analytical specificity in evaluating for the presence of increased urinary 3-OHGA. This second-tier approach, using a GC isothermal hold, could easily be implemented or adapted by other clinical laboratories experiencing related diagnostic challenges.

Global developmental delay and intellectual disability (GDD/ID) affect 3% of the paediatric population. Although inborn errors of metabolism (IEM) are not a common cause of GDD/ID, early therapeutic intervention can improve neurodevelopmental manifestations. In 2012, a first-tier test panel, including specialized metabolic and routine chemistry tests, was piloted to community-based paediatricians in British Columbia with aims to achieve earlier diagnosis of treatable IEM.OBJECTIVE:The aim of this retrospective review was to evaluate the diagnostic yield from these first-tier tests in the 7 years before (2006 to 2012) and after (2013 to 2019) implementation at the community paediatrician level.RESULTS:Prior and postimplementation diagnostic yield of an IEM from first-tier metabolic testing was 9 out of 986 (0.91%) and 11 out of 4,345 children (0.25%), respectively. Disorders of creatine metabolism and organic acidurias were the most frequently established diagnoses in both time periods. No diagnoses were established through acylcarnitine copper/ceruloplasmin, lactate, or ammonia testing. Twenty out of 24 patients had specific neurological or other red flag signs in addition to GDD/ID. Four boys diagnosed with an x-linked creatine transporter defect (CTD) had speech-language delay as the most prominent finding.CONCLUSIONS:The expansion of first-tier metabolic testing to community-based paediatricians in BC did not yield an increase in IEM diagnoses. A modified first-tier test panel should be offered to patients with GDD/ID, neurologic, and/or red flag signs. Urine creatine testing in boys with speech-language delay warrants consideration to detect CTD.

The presence of ketone bodies (KBs) can interfere with creatinine (Cr) measurement in both enzymatic and Jaffe methods. Since a high proportion of children hospitalized for diabetic ketoacidosis (DKA) develop acute kidney injury (AKI), here we investigate whether KB interferences affect the accuracy of pediatric Cr measurement. Residual patient plasma samples were pooled to make three Cr levels (~ 50, 100, and 250 μM). KBs (acetone, acetoacetate, and β-hydroxybutyrate) were used to spike the pooled samples. All samples were measured for Cr by two enzymatic methods (E1 and E2), two Jaffe methods (J1 and J2), and LC–MS/MS. LC–MS/MS was considered the gold standard, and the % difference in Cr concentration was calculated for each method. E1 and E2 were unaffected by the presence of all three KBs. J1 and J2 were unaffected by the presence of β-hydroxybutyrate. The presence of acetone resulted in dose-dependent positive interference in both Jaffe methods, whereas the presence of acetoacetate resulted in dose-dependent positive and negative interference in J1 and J2, respectively. Compared to the enzymatic methods, the Jaffe methods were much more susceptible to interference by acetone and acetoacetate, especially at lower Cr values which are commonly seen in pediatrics. Interpretation of changes in Cr concentration between different hospitals when transferring patients can become ambiguous and true kidney function unclear if different methods are used without awareness of method-specific biases. To improve DKA patient care, we recommend standardizing all of the Cr methods to an enzymatic method. A higher resolution version of the Graphical abstract is available as Supplementary information

Abstract: Importance: Measuring humoral immunogenicity of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) vaccines and finding population-level correlates of protection against coronavirus disease (COVID-19) presents an immediate challenge to public health practitioners. Objective: To study the diagnostic accuracy and predictive value of finger prick capillary dried blood spot (DBS) samples tested using an anti-immunoglobulin G (IgG) serology assay to measure SARS-CoV-2 seropositivity and the humoral immunogenicity of COVID-19 vaccination. Design, Setting and Participants: This cross-sectional study enrolled participants (n= 644) who had paired DBS and serum samples collected by finger prick and venipuncture, respectively, in British Columbia, Canada between January 12th, 2020 and May 21st, 2021. Samples were tested by a multiplex electrochemiluminescence assay for SARS-CoV-2 anti-Spike (S), -Nucleocapsid (N) and -receptor binding domain (RBD) IgG reactivity using a Meso Scale Discovery (MSD) platform. Additionally, unpaired DBS samples (n= 6,706) that were collected in the province during the same time period were included for analysis of SARS-CoV-2 anti-N IgG reactivity. Exposure: Collection of a capillary DBS by finger prick alone or paired with serum by venipuncture. Outcome: Humoral immune response to SARS-CoV-2 measured by detection of anti-S, -N or -RBD IgG. Results: In comparison to a paired-serum reference, DBS samples possessed a sensitivity of 80% (95% CI: 61%-91%) and specificity of 97% (95% CI: 95%-98%). Receiver operator characteristic curve analysis (ROC) found that participant DBS samples tested for anti-SARS-CoV-2 IgG by MSD V-PLEX COVID-19 Coronavirus Panel 2 assay accurately classify SARS-CoV-2 seroconversion at an 88% percent rate, AUC= 88% (95% CI: 81%-96%). Modelling found that a DBS-based testing approach has a high positive predictive value (PPV) (98% [95% CI: 98%-99%]) in a theoretical population with seventy-five percent COVID-19 vaccine coverage. At lower vaccine coverages of fifteen and forty-five percent, the test's PPV decreased and the negative predictive value increased. Conclusion: We demonstrate that DBS samples, when tested using an electrochemiluminescence assay, provide a valid alternative to traditional venipuncture and should be considered to reliably detect SARS-CoV-2 seropositivity.

Inborn errors of propionate, cobalamin and methionine metabolism are targets for Newborn Screening (NBS) in most programs world-wide, and are primarily screened by analyzing for propionyl carnitine (C3) and methionine in dried blood spot (DBS) cards using tandem mass spectrometry (MS/MS). Single-tier NBS approaches using C3 and methionine alone lack specificity, which can lead to an increased false-positive rate if conservative cut-offs are applied to minimize the risk of missing cases. Implementation of liquid chromatography tandem mass spectrometry (LC-MS/MS) second-tier testing for 2-methylcitric acid (MCA), methylmalonic acid (MMA), and homocysteine (HCY) from the same DBS card can improve disease screening performance by reducing the false-positive rate and eliminating the need for repeat specimen collection. However, DBS analysis of MCA, MMA, and HCY by LC-MS/MS is challenging due to limited specimen size and analyte characteristics leading to a combination of low MS/MS sensitivity and poor reverse-phase chromatographic retention. Sufficient MS response and analytical performance can be achieved for MCA by amidation using DAABD-AE and by butylation for MMA and HCY. Herein we describe the validation of a second-tier dual derivatization LC-MS/MS approach to detect elevated MCA, MMA, and HCY in DBS cards for NBS. Clinical utility was demonstrated by retrospective analysis of specimens, an interlaboratory method comparison, and assessment of external proficiency samples. Imprecision was <10.8% CV, with analyte recoveries between 90.2 and 109.4%. Workflows and analytical performance characteristics of this second-tier LC-MS/MS approach are amenable to implementation in the NBS laboratory.

Vitamin B12 (B12) is a co-enzyme essential for fetal growth and development. Lower maternal B12 status has been associated with preterm birth (<37 gestational weeks) and low birth weight (<2500 g), which are linked to morbidity and mortality across the lifespan. In Canada, 17-25 % of women in early pregnancy had a serum total B12 concentration <148 pmol/l and maternal total B12 concentration decreased throughout pregnancy. This study aimed to determine the association between maternal B12 status and birth outcomes in Canadian mother-newborn dyads. A secondary analysis of 709 mother-newborn dyads in British Columbia (BC), Canada, was conducted. Bio-banked first- (n 656) and second-trimester (n 709) maternal serum samples of apparently healthy South Asian (50 %) and European (50 %) women from the BC Prenatal Genetic Screening Program were quantified for B12 biomarkers (total B12, holotranscobalamin (holoTC), methylmalonic acid (MMA) and total homocysteine (tHcy)). Obstetric history and birth outcome data were obtained from the BC Perinatal Data Registry. All associations were determined using multiple linear regression. Maternal serum total B12, holoTC, MMA and tHcy had a mean weekly decrease of 3·64 pmol/l, 1·04 pmol/l, 1·44 nmol/l and 0·104 μmol/l, respectively (P < 0·001). Despite a total B12 concentration <148 pmol/l among 20-25 % of the women, maternal B12 biomarker concentrations were not associated with birth weight z-score, head circumference z-score and gestational age at birth (P > 0·05). Additional research in women at high risk of adverse birth outcomes and the association between maternal B12 status and functional, for example, cognitive, outcomes is needed.

Serum total vitamin B12 (tB12) is the most commonly used biomarker to assess B12 status in healthy and patient populations but there is ambiguity as to its performance for early and reliable B12 deficiency diagnosis. Holotranscobalamin (holoTC) is the B12 form taken up by cells and may be a more sensitive B12 indicator. This descriptive, prospective study aimed to compare serum tB12 with serum holoTC concentration in their ability to detect functional B12 deficiency defined as elevated methylmalonic acid (MMA) concentration in a pediatric population at risk of B12 deficiency. A total of 26 infants and children aged 3 mo-15 yrs with a history of ileal resection were recruited from the Children's Intestinal Rehabilitation Program at the British Columbia Children's Hospital, Canada. Between 1 to 7 samples per patient were collected over 2yrs, with complete biomarker data for 41 samples. Clinical, anthropometric and dietary data were also collected. Age-specific reference limits derived from a healthy pediatric reference sample were used as cut-offs to categorize B12 deficiency. Of the 41 samples, 29 (71%) had concordant biomarker results all indicating adequate B12 status. Elevated MMA (>398 nmol/L) was found in only 2 samples and those had holoTC concentration indicative of B12 deficiency (<40 pmol/L) but normal tB12 (>209 pmol/L). While holoTC exceeded tB12 in sensitivity for the detection of functional B12 deficiency, holoTC had reduced specificity, 75% compared to 85% for tB12, leading to a reduced positive predictive value (22%). Patients receiving total parenteral nutrition (TPN) had significantly higher tB12 but similar holoTC concentration compared to those not receiving TPN. Overall, the results suggest that serum holoTC detects patients with elevated MMA indicative of B12 deficiency, who are not identified by tB12 concentration, in children with short bowel syndrome. It also suggests that the current cut-off for tB12 may be too low. These descriptive findings warrant further evaluation and validation of B12 biomarkers and related cutoffs for adequate, suboptimal and deficient B12 status. Healthy Starts Catalyst Grant from the British Columbia Children's Hospital Research Institute, Vancouver BC, Canada.

BACKGROUND:Oxythiamine is a uremic toxin that acts as an antimetabolite to thiamine and has been associated with cases of Shoshin beriberi syndrome in adults. We sought to identify whether surgical stress and ischemia/reperfusion injury may precipitate functional thiamine deficiency in children peritransplant.METHODS:We retrospectively analyzed a cohort of pediatric kidney transplant recipients. Oxythiamine levels were measured in pre-transplant serum samples by mass spectrometry and tested for association with severity of lactic acidosis in the first 24 h post-transplant. Secondary outcomes included association with hyperglycemia and indicators of dialysis adequacy (DA).RESULTS:Forty-seven patients were included in the analysis. Median oxythiamine levels differed by modality, measuring 0.67 nM (IQR 0.31, 0.74), 0.34 nM (IQR 0.28, 0.56), and 0.25 nM (IQR 0.17, 0.38) for peritoneal dialysis (PD), hemodialysis (HD), and no dialysis, respectively (p = 0.05). Oxythiamine was associated with 24-h lactate levels (r = 0.38, p = 0.02) and negatively associated with DA (r = - 0.44, p = 0.02). Median oxythiamine levels were higher in patients with poor DA (0.92 nM (IQR 0.51, 1.01) vs. 0.40 nM (IQR 0.24, 0.51), p < 0.01). Sensitivity analysis showed absence of residual association of oxythiamine with 24-h lactate or dialysis modality, but remained significant for DA (p = 0.03). One patient manifested Shoshin beriberi syndrome (oxythiamine 2.03 nM).CONCLUSIONS:Oxythiamine levels are associated with DA at transplant. Patients on PD with no residual kidney function and low DA manifest the highest oxythiamine levels and may be at an increased risk for developing acute Shoshin beriberi syndrome in the early post-transplant period.

One of the most dramatic discoveries in metabolic disease research was that of Ashbørn Følling, who in 1934, published his research outlining unusual biochemical findings in a set of siblings with severe developmental delay [...].

Objectives To evaluate the clinical impact of a congenital adrenal hyperplasia (CAH) newborn screening program and incremental costs relative to benefits in screened vs unscreened infants. We hypothesized that screening would lead to clinical benefits and would be cost effective. Study design This was an ambispective cohort study at British Columbia Children's Hospital, including infants diagnosed with CAH from 1988-2008 and 2010-2018. Data were collected retrospectively (unscreened cohort) and prospectively (screened cohort). Outcome measures included hospitalization, medical transport, and resuscitation requirements. The economic analysis was performed using a public payer perspective. Results Forty unscreened and 17 screened infants were diagnosed with CAH (47% vs 53% male). Median days to positive screen was 6 and age at diagnosis was 5 days (range, 0-30 days) and 6 days (range, 0-13 days) in unscreened and screened populations, respectively. In unscreened newborns, 55% required transport to a tertiary care hospital, 85% required hospitalization, and 35% required a fluid bolus compared with 29%, 29%, and 12% in screened infants, respectively. The cost of care was $33 770 per case in unscreened vs $17 726 in screened newborns. In the screened cohort, the incremental cost-effectiveness ratio was $290 in the best case analysis and $4786 in the base case analysis, per hospital day avoided. Conclusions Compared with unscreened newborns, those screened for CAH were less likely to require medical transport and had shorter hospital stays. Screening led to a decrease in hospitalization costs. Although screening did not result in cost savings, it was assessed to be cost effective considering the clinical benefits and incremental cost-effectiveness ratio.

Newborn screening for Cystic Fibrosis has been implemented in most programs worldwide, but the approach used varies, including combinations of immunoreactive trypsinogen (IRT) and CFTR mutation analysis on one or more specimens. The British Columbia (BC) newborn screening program tests ~45,000 infants per year in BC and the Yukon Territory, covering almost 1.5 million km2 in western Canada. CF screening was initiated using an IRT-DNA-IRT approach with a second bloodspot card at 21 days of age for all CFTR mutation heterozygotes and any non-carriers in the top 0.1% for IRT. This second IRT was implemented to avoid sweat testing of infants without persistent hypertrypsinemia, reducing the burden of travel for families. Over nine years (2010–2018), 401,977 infants were screened and CF was confirmed in 76, and a further 28 were deemed CF screen positive inconclusive diagnosis (CFSPID). Day 21 IRT was normal in 880 CFTR mutation carriers who were quoted a very low CF risk and offered optional sweat testing. Only 13% of families opted for sweat testing and a total of 1036 sweat tests were avoided. There were six false negative CF cases (and three CFSPID) due to a low initial IRT or no CFTR mutations. Although one CFSPID case had a normal repeat IRT result, the addition of the day 21 IRT did not contribute to any CF false negatives.

Background: As a methyl donor required in the folate-vitamin B-12 independent remethylation of total homocysteine (tHc gamma) to methionine, betaine is critical for fetal development. Pregnant South Asian women living in Canada had a higher reported prevalence of low vitamin B-12 status compared with Europeans; betaine concentrations in this population are unknown. Objectives: We aimed to compare serum betaine concentrations between South Asian and European pregnant women, and to determine the relation between betaine and tHc gamma concentrations in early pregnancy. Methods: A retrospective cohort study was conducted using biobanked serum samples of 723 apparently healthy pregnant women of South Asian (50%) and European ethnicity residing in British Columbia, Canada. Betaine, dimethylglycine (DMG), tHc gamma, and related metabolites were quantified in samples collected in the first (8-13 weeks of gestation) and second (14-20 weeks of gestation) trimesters. The relation between betaine and tHc gamma concentrations was assessed using a generalized regression model adjusted for weeks of gestation, ethnicity, prepregnancy BMI, maternal age, neonatal sex, parity, total vitamin B-12, folate, pyridoxal 5'-phosphate, and methionine concentrations. Results: Median serum concentrations of betaine and its metabolite DMG were higher in South Asian women in the first (19.8 [IQR: 16.3-25.0] and 1.55 [IQR: 1.30-1.96] mu mol/L, respectively) and second trimesters (16.1 [IQR: 12.9-19.8] and 1.42 [IQR: 1.14-1.81] mu mol/L, respectively) compared with European women (17.6 [IQR: 13.7-22.6] and 1.38 [IQR: 1.12-1.77] mu mol/L, respectively) and (12.9 [IQR: 10.6-16.7] and 1.19 [IQR: 0.97-1.52] mu mol/L, respectively; all P values < 0.0001). Betaine was inversely associated with tHc gamma concentration (beta=-0.0208; 95% CI: -0.0341, -0.00742; P = 0.002). Additionally, total vitamin B-12 was associated with tHc gamma concentration (beta = -0.0312; 95% CI: -0.0401, -0.0224), after adjusting for confounding factors. Conclusions: Pregnant South Asian women residing in Canada had higher betaine and DMG concentrations, compared with women of European ethnicity, while betaine and total vitamin B-12 predicted tHc gamma independent of ethnicity. Our results emphasize the role of betaine, as methyl donor, in the remethylation of tHc gamma in a folate-replete population.