Sweat testing infants detected by cystic fibrosis newborn screening

Sweat conductivity for diagnosing cystic fibrosis after positive newborn screening: prospective, diagnostic test accuracy study

OBJECTIVE

To assess the accuracy of sweat conductivity among newborns and very young infants.

DESIGN

Prospective, population-based, diagnostic test accuracy study.

SETTING

Public Statewide Newborn Screening Programme where the incidence rate of cystic fibrosis (CF) is ≈1:11 000.

PATIENTS

Newborns and very young infants with positive two-tiered immunoreactive trypsinogen.

INTERVENTIONS

Sweat conductivity and sweat chloride were performed simultaneously, on the same day and facility by independent technicians, with the cut-off values of 80 mmol/L and 60 mmol/L, respectively.

MAIN OUTCOME MEASURES

Sensitivity, specificity, positive and negative predictive values (PPV and NPV), overall accuracy, positive and negative likelihood ratios (+LR, -LR) and post (sweat conductivity (SC)) test probability were calculated to assess SC performance.

RESULTS

1193 participants were included, 68 with and 1108 without CF, and 17 with intermediate values. The mean (SD) age was 48 (19.2) days, ranging from 15 to 90 days. SC yielded sensitivity of 98.5% (95% CI 95.7 to 100), specificity of 99.9% (95% CI 99.7 to 100), PPV of 98.5% (95% CI 95.7 to 100) and NPV of 99.9% (95% CI 99.7 to 100), overall accuracy of 99.8% (95% CI 99.6 to 100), +LR of 1091.7 (95% CI 153.8 to 7744.9) and -LR of 0.01 (95% CI 0.00 to 0.10). After a positive and negative sweat conductivity result, the patient's probability of CF increases around 350 times and drops to virtually zero, respectively.

CONCLUSION

Sweat conductivity had excellent accuracy in ruling in or ruling out CF after positive two-tiered immunoreactive trypsinogen among newborns and very young infants.

Processing Newborn Bloodspot Screening Results for CF

Every newborn bloodspot screening (NBS) result for cystic fibrosis (CF) consists of two parts: a screening part in the laboratory and a clinical part in a CF centre. When introducing an NBS programme, more attention is usually paid to the laboratory part, especially which algorithm is most suitable for the region or the country. However, the clinical part, how a positive screening result is processed, is often underestimated and can have great consequences for the affected child and their parents. A clear algorithm for the diagnostic part in CF centres is also important and influences the performance of a CF NBS programme. The processing of a positive screening result includes the initial information given to the parents, the invitation to the sweat test, what to do if a sweat test fails, information about the results of the sweat test, the inconclusive diagnosis and the carrier status, which is handled differently from country to country. The time until the definitive diagnosis and adequate information is given, is considered by the parents and the CF team as the most important factor. The communication of a positive NBS result is crucial. It is not a singular event but rather a process that includes ensuring the appropriate clinicians are aware of the result and that families are informed in the most efficient and effective manner to facilitate consistent and timely follow-up.

Comparison of two sweat test systems for the diagnosis of cystic fibrosis in newborns

OBJECTIVES

In the national newborn screening programme for CF in Switzerland, we compared the performance of two sweat test methods, by investigating the feasibility and diagnostic performance of the Macroduct^® collection method (with chloride mesurement) and Nanoduct^® test (measuring conductivity) for diagnosing CF.

STUDY-DESIGN

We included all newborns with a positive screening result between 2011 and 2015 who were referred to a CF-centre for sweat testing. In the CF-centre, a Macroduct and Nanoduct sweat test were performed simultaneously. If sweat test results were positive or borderline, a DNA analysis was performed. Final diagnosis was based on genetic mutations.

RESULTS

Over 5 years, 445 children were screened positive and in 413 (114 with CF) at least one sweat test was performed (median age at first test, 22 days); both tests were performed in 371 children. A sweat test result was more often available with the Nanoduct compared to the Macroduct (79 vs 60%, P < 0.001). The Nanoduct was equally sensitive as the Macroduct in identifying newborns with CF (sensitivity 98 vs 99%) but less specific (specificity 79 vs 93%; P-value comparing ROC curves = 0.033).

CONCLUSIONS

This national multicentre study revealed high failure rates for Macroduct and Nanoduct in newborns in real life practice. While this needs to be addressed, our results suggested that performing the Nanoduct in addition to the Macroduct might speed up the diagnostic process because it more often yields valid results with comparable diagnostic performance. The addition of the Nanoduct sweat test can therefore help to reduce the stressful time of uncertainty for parents and to start appropriate treatment earlier.

Cystic Fibrosis Diagnostic Challenges over 4 Decades: Historical Perspectives and Lessons Learned

OBJECTIVE

Because cystic fibrosis (CF) can be difficult to diagnose, and because information about the genetic complexities and pathologic basis of the disease has grown so rapidly over the decades, several consensus conferences have been held by the US CF Foundation, and a variety of other efforts to improve diagnostic practices have been organized by the European CF Society. Despite these efforts, the application of diagnostic criteria has been variable and caused confusion.

STUDY DESIGN

To improve diagnosis and achieve standardization in terms and definitions worldwide, the CF Foundation in 2015 convened a committee of 32 experts in the diagnosis of CF from 9 countries. As part of the process, all previous consensus-seeking exercises sponsored by the CF Foundation, along with the important efforts of the European CF Society, were comprehensively and critically reviewed. The goal was to better understand why consensus conferences and their publications have not led to the desired results.

RESULTS

Lessons learned from previous diagnosis consensus processes and products were identified. It was decided that participation in developing a consensus was generally not inclusive enough for global impact. It was also found that many efforts to address sweat test issues were valuable but did not always improve clinical practices as CF diagnostic testing evolved. It also became clear from this review that premature applications of potential diagnostic tests such as nasal potential difference and intestinal current measurement should be avoided until validation and standardization occur. Finally, we have learned that due to the significant and growing number of cases that are challenging to diagnose, an associated continuing medical education program is both desirable and necessary.

CONCLUSIONS

It is necessary but not sufficient to organize and publish CF diagnosis consensus processes. Follow-up implementation efforts and monitoring practices seem essential.

Diagnostic Testing in Cystic Fibrosis

Cystic Fibrosis (CF) is a rare, multisystem disease leading to significant morbidity and mortality. CF is caused by defects in the cystic fibrosis transmembrane conductance regulator protein (CFTR), a chloride and bicarbonate transporter. Early diagnosis and access to therapies provides benefits in nutrition, pulmonary health, and cognitive ability. Several screening and diagnostic tests are available to support a diagnosis. We discuss the characteristics of screening and diagnostic tests for CF and guideline-based algorithms using these tools to establish a diagnosis. We discuss classification and management of common "diagnostic dilemmas," including the CFTR-related metabolic syndrome and other CFTR-associated diseases.

Clinical evaluation of the Nanoduct sweat test system in the diagnosis of cystic fibrosis after newborn screening

After a positive newborn screening test for cystic fibrosis (CF), a sweat test is performed to confirm the diagnosis. The success rate of the generally acknowledged methods (Macroduct/Gibson and Cooke) in newborns varies between 73 and 99%. The Nanoduct sweat test system is easier to perform and less sweat is needed. The main aim of this study was to measure the success rate of the Nanoduct compared to current approved sweat test methods in a newborn population. After informed consent of the parents, newborns with a positive screening test for CF were included. The Macroduct or Gibson and Cooke and Nanoduct were performed in all infants, during the same appointment. The chloride concentration was determined by standard coulorimetry; conductivity was measured directly and converted to a NaCl molarity. One hundred eight newborns were included: 17 with CF, 7 with cystic fibrosis transmembrane regulator (CFTR)-related metabolic syndrome (CRMS), and 84 healthy children. The success rate of the Nanoduct was 93% and for the Macroduct/Gibson and Cooke 79% (McNemar, p = 0.002). The Nanoduct detected the same CF patients as the Macroduct/Gibson and Cooke; one CF patient had an equivocal result for both tests, and no patients were missed. The area under the receiver operating characteristic curve for detection of CF with the Nanoduct was 0.999, with ideal cutoff levels of 91 and 66 mmol/l, comparable to former studies.

CONCLUSION

The success rate of the Nanoduct to collect sufficient sweat in infants was higher compared to the Macroduct and Gibson and Cooke.

Improving the Rate of Sufficient Sweat Collected in Infants Referred for Sweat Testing in Michigan

Objective. Sweat collected for testing should have quantity not sufficient (QNS) rate of ≤10% in babies ≤3 months of age. Michigan (MI) cystic fibrosis (CF) centers' QNS rates were 12% to 25% in 2009. This project was initiated to reduce sweat QNS rates in MI. Methods/Steps. (a) Each center's sweat testing procedures were reviewed by a consultant. (b) Each center received a report with recommendations to improve QNS rates. (c) Technicians visited other participating centers to observe their procedures. Results. A total of 778 infants were identified as positive via CF newborn screening over a 2-year period. The mean age at time of sweat test was 23.2 days (SD ± 13.0 days). The overall QNS percent decreased from 14.4% to 9.5% (P = .04) during the study. Conclusion. This project and teamwork approach led to a decrease of sweat test QNS rates, opportunities to solve a common problem, and improved quality of care.

A new method of sweat testing: the CF Quantum®sweat test

BACKGROUND

Conventional methods of sweat testing are time consuming and have many steps that can and do lead to errors. This study compares conventional sweat testing to a new quantitative method, the CF Quantum® (CFQT) sweat test. This study tests the diagnostic accuracy and analytic validity of the CFQT.

METHODS

Previously diagnosed CF patients and patients who required a sweat test for clinical indications were invited to have the CFQT test performed. Both conventional sweat testing and the CFQT were performed bilaterally on the same day. Pairs of data from each test are plotted as a correlation graph and Bland-Altman plot. Sensitivity and specificity were calculated as well as the means and coefficient of variation by test and by extremity. After completing the study, subjects or their parents were asked for their preference of the CFQT and conventional sweat testing.

RESULTS

The correlation coefficient between the CFQT and conventional sweat testing was 0.98 (95% confidence interval: 0.97-0.99). The sensitivity and specificity of the CFQT in diagnosing CF was 100% (95% confidence interval: 94-100%) and 96% (95% confidence interval: 89-99%), respectively. In one center in this three center multicenter study, there were higher sweat chloride values in patients with CF and also more tests that were invalid due to discrepant values between the two extremities. The percentage of invalid tests was higher in the CFQT method (16.5%) compared to conventional sweat testing (3.8%) (p < 0.001). In the post-test questionnaire, 88% of subjects/parents preferred the CFQT test.

CONCLUSIONS

The CFQT is a fast and simple method of quantitative sweat chloride determination. This technology requires further refinement to improve the analytic accuracy at higher sweat chloride values and to decrease the number of invalid tests.

Relationship between sweat chloride, sodium, and age in clinically obtained samples

BACKGROUND

The relationship between sweat electrolytes and age is uncertain, as is the value of measuring sodium or the chloride:sodium ratio.

METHODS

13,785 sweat tests performed over 23 years at one center through the Macroduct collection in clinically obtained samples were analyzed.

RESULTS

Sweat chloride tended to decrease over the first year of life, slowly increase until the fourth decade, then either level off or slightly decrease. In children, sweat sodium overlapped between those with positive and negative sweat tests, but not in adults. If the sweat test was positive, there was a higher likelihood of having a chloride:sodium ratio >1, but most subjects with a ratio >1 did not have CF.

CONCLUSIONS

Sweat chloride and sodium vary with age. Measurement of sweat sodium did not add discriminatory value. The proportion of subjects with a chloride:sodium ratio >1, with or without CF, varied greatly between age ranges.

Effects of immediate telephone follow-up with providers on sweat chloride test timing after cystic fibrosis newborn screening identifies a single mutation

OBJECTIVE

To assess whether reporting "possible cystic fibrosis (CF)" newborn screening (NBS) results via fax plus simultaneous telephone contact with primary care providers (PCPs) versus fax alone influenced 3 outcomes: undergoing a sweat chloride test, age at sweat chloride testing, and undergoing sweat testing before age 8 weeks.

STUDY DESIGN

This was a retrospective cohort comparison of infants born in Wisconsin whose PCP received a telephone intervention (n = 301) versus recent historical controls whose PCP did not (n = 355). Intervention data were collected during a longitudinal research and quality improvement effort; deidentified comparison data were constructed from auxiliary NBS tracking information. Parametric and nonparametric statistical analyses were performed for group differences.

RESULTS

Most infants (92%) with "possible CF" NBS results whose PCP lacked telephone intervention ultimately underwent sweat testing, underlining efficacy for fax-only reporting. Telephone intervention was significantly associated with improvements in the infants undergoing sweat testing at age ≤6 weeks and <8 weeks and a slight, statistically nonsignificant 3.5-day reduction in the infants' age at sweat testing. The effect of telephone intervention was greater for PCPs whose patients underwent sweat testing at community-affiliated medical centers versus those whose patients did so at academic medical centers (P = .008).

CONCLUSION

Reporting "possible CF" NBS results via fax plus simultaneous telephone follow-up with PCPs increases the rate of sweat chloride testing before 8 weeks of age, when affected infants are more likely to receive full benefits of early diagnosis and treatment.

Comparison of quantitative sweat chloride methods after positive newborn screen for cystic fibrosis

OBJECTIVES

Rapid and reliable confirmatory sweat testing following a positive newborn screen (NBS) for cystic fibrosis (CF) is preferred to allow for early diagnosis and to decrease parental anxiety. The Cystic Fibrosis Foundation (CFF) recently recommended a quantity not sufficient (QNS) rate of ≤ 10% in infants <3 months of age referred for quantitative sweat chloride analysis. Two CFF-approved methods are available by which to quantitatively measure chloride concentration in sweat. Our objective was to compare the performance of the Macroduct® sweat collection system (MSCS) with the Gibson and Cooke technique (GCT) in the acquisition of samples for the determination of sweat chloride concentration in infants with a positive Minnesota State NBS for CF.

METHODS

A retrospective database review of infants referred to the core Minnesota CF Center or its affiliate site for confirmatory sweat testing was performed to compare the QNS rates for the two techniques. Associations between birthweight, age at test, race, and QNS rates were examined.

RESULTS

Five hundred sixty-eight infants were referred for 616 sweat tests from March 2006 to January 2010. The mean age was 32.8 days at the initial sweat test. The GCT had a significantly higher QNS rate compared to the MSCS (15.4% vs. 2.1%, P < 0.0001). There was no association between age and the probability of QNS. The probability of QNS decreased as birthweight increased (P = 0.02). After adjusting for age, the odds of QNS using the GCT remained 8.34 (95% CI: 3.72-18.71) times that of the MSCS. Non-White infants had a significantly higher likelihood of QNS compared to non-Hispanic White infants (P = 0.0025).

CONCLUSIONS

Given the performance of the MSCS, the Minnesota CF Center has implemented the MSCS as its method of choice for diagnostic sweat testing in infants following a positive state NBS.

Cystic fibrosis newborn screening: distribution of blood immunoreactive trypsinogen concentrations in hypertrypsinemic neonates

The IRT screening test for the use in diagnosing newborns with CF has a high sensitivity but is not very specific resulting in a large number of screened positive infants found to have a normal sweat test. The aim of this study was to analyze the differences in b-IRT levels among different groups of newborns positive to NBS.Population data included all b-IRT positive (>99th centile) neonates born in Lombardia from 2000 to 2007. The hypertrypsinemic newborns were divided into four groups, according to CF status (noncarrier, carrier, CFTR-RD, CF).Among a total of 717,172 newborns screened within the study period, 7,354 newborns were found positive to NBS and were included in the study. An overall statistically significant difference in b-IRT levels was found among the four groups (p < 0.001), while b-IRT values did not differ between noncarriers and carriers. b-IRT levels had a low predictive accuracy in correctly identifying the four different groups (c-index: 0.60), but the accuracy was high in discriminating between classic CF and carrier or noncarrier status in neonates positive to NBS. The IRT level on the initial blood specimen obtained at birth differs based on the CF genotype, although a wide range of individual variation may occur.

Factors associated with parental perception of child vulnerability 12 months after abnormal newborn screening results

We identified factors associated with elevated parental perceptions of child vulnerability (PPCV) 12 months after newborn screening (NBS) of 136 children: healthy, normal results (H, n = 37), cystic fibrosis carriers (CF-C, n = 40), congenital hypothyroidism (CH, n = 36), and cystic fibrosis (CF, n = 23). Controlling for infant and parent characteristics, mixed logit structural equation modeling showed direct paths to elevated PPCV included parent female sex, CF diagnosis, and high documented illness frequency. PPCV was positively associated with maternal parenting stress. Infants with CF and CF carriers had significantly more documented illness frequency than H group infants. The CH group did not differ significantly from the H group and had no paths to PPCV. Unexpectedly high documented illness frequency among infants who are CF carriers warrants further investigation.

Predictors of insufficient sweat production during confirmatory testing for cystic fibrosis

Michigan's Newborn Screening (NBS) Program began statewide screening for cystic fibrosis (CF) in October 2007. Confirmatory sweat testing is performed in infants having initial immunoreactive trypsinogen concentrations ≥ 99.8th percentile or ≥ 96 th percentile and at least one CF mutation identified by DNA analysis. Some infants fail to produce a sufficient quantity of sweat (QNS-quantity not sufficient) to test for CF, meaning disease confirmation is delayed and sweat testing is later repeated. In this study, we evaluate predictors of QNS results. Information from the linked birth certificates and NBS diagnostic confirmation data were used. The study population was resident infants born in Michigan in 2008 who underwent a sweat test. Bivariate analyses revealed that preterm birth, low birth weight, CF care center, and race were significantly associated with QNS sweat testing results. Adjusted analyses indicated that preterm infants were 2.4 times more likely to have QNS results (95% CI 0.9, 6.4). When age at time of test, accounting for gestational age (gestational age at delivery plus postdelivery age of life=corrected age), was used in the multivariable model, infants <39 weeks were 7.4 times more likely to have QNS results (95% CI 2.5, 21.8). Waiting to sweat test until an infant is aged 39 weeks or more (corrected age) would likely reduce the rate of QNS results, thereby reducing the burden of repeat sweat testing on families and healthcare providers. Further research is necessary to understand the impact of potential delays in diagnosis/treatment relative to postponing sweat testing.

The need for quality improvement in sweat testing infants after newborn screening for cystic fibrosis

The proportion of insufficient sweat tests after positive newborn screening for cystic fibrosis was determined. Infants ≤ 3 months old had a mean (± standard deviation) rate of 7.2% (± 7.6) (range, 0% to 40%). Collection methods did not affect the rates. The high and variable rates indicate a need for quality improvement.

Physiological measurements confirming the diagnosis of cystic fibrosis: the sweat test and measurements of transepithelial potential difference

Post-natal screening allied with genetic mutation testing has altered our perception of cystic fibrosis (CF) as a clinical entity. Increasingly, infants identified through screening programmes have few or no symptoms or present with atypical forms of the disease. We review how the sweat test has evolved to be the gold standard for confirming the diagnosis of CF and examine its limitations. Other physiological measurements, including nasal potential difference and intestinal current measurement, which might aid in establishing the diagnosis, particularly in patients exhibiting a mild phenotype, are also considered.

A reference interval for sweat chloride in infants aged between five and six weeks of age

Background

This study was designed to establish a reference interval for sweat chloride for infants without evidence of cystic fibrosis (CF), aged between 5 wk and 6 wk, a time when sweat testing is an integral part of newborn screening for CF. In addition, we compared the gold standard method of sweat testing (quantitative pilocarpine iontophoresis [QPIT, coulometry]) with an emerging methodology (Macroduct™ [ISE]).

Methods

This was a prospective study on healthy infants at 5–6 wk of age. Sweat collection was undertaken at home on both outer thigh areas using two methods (QPIT and Macroduct™). The order of testing was randomly assigned. Filter paper samples (QPIT) were analysed using flame photometry and coulometry. Macroduct™ samples were analysed using ion-selective electrodes (ISE, Abbott Architect c8000, UK).

Results

Insufficient sweat was collected on 28 occasions with the QPIT (coulometry) method and on 31 with the Macroduct™ (ISE) capillary system. We achieved a 92% success rate in undertaking two sweat collections consecutively (n = 177). Sweat chloride concentrations were normally distributed with excellent limits of agreement between the two methods of sweat collection and analysis (n = 150). Median (IQR) sweat chloride was 11.2 mmol/L (8–13) with QPIT (coulometry) method with a 99.5th centile (n = 165) of 24 mmol/L.

Conclusion

The Macroduct™ (ISE) capillary sweat collection system is valid in this age group. Sweat chloride concentrations above 30 mmol/L should prompt assessment in a specialist CF centre.

Guidelines for diagnosis of cystic fibrosis in newborns through older adults: Cystic Fibrosis Foundation consensus report

Newborn screening (NBS) for cystic fibrosis (CF) is increasingly being implemented and is soon likely to be in use throughout the United States, because early detection permits access to specialized medical care and improves outcomes. The diagnosis of CF is not always straightforward, however. The sweat chloride test remains the gold standard for CF diagnosis but does not always give a clear answer. Genotype analysis also does not always provide clarity; more than 1500 mutations have been identified in the CF transmembrane conductance regulator (CFTR) gene, not all of which result in CF. Harmful mutations in the gene can present as a spectrum of pathology ranging from sinusitis in adulthood to severe lung, pancreatic, or liver disease in infancy. Thus, CF identified postnatally must remain a clinical diagnosis. To provide guidance for the diagnosis of both infants with positive NBS results and older patients presenting with an indistinct clinical picture, the Cystic Fibrosis Foundation convened a meeting of experts in the field of CF diagnosis. Their recommendations, presented herein, involve a combination of clinical presentation, laboratory testing, and genetics to confirm a diagnosis of CF.

Targeted extended cystic fibrosis mutation testing on known and at-risk patients and relatives

This paper reports mathematically derived residual risks of being a carrier or being affected with cystic fibrosis following various screening scenarios to assist in interpreting test results and advising patients. While parental screening with 23 American College of Medical Genetics (ACMG) cystic fibrosis mutations defines the 64% of affected U.S. Caucasian fetuses with two detectable mutations, newborn screening for elevated immunoreactive trypsinogen (IRT) and sweat chloride identifies an additional 36% of affected newborns with zero or one detected mutation. The relatives of these affected newborns with less than two detectable mutations have higher posterior (after) 23 mutation-negative test risks of carrying undetected mutations. These calculations emphasize how knowledge of the mutations in the related affected patient substantially improves upon the quality of after-test advice to patients. Furthermore, negative tests of the partner without a family history and/or more extensive cystic fibrosis transmembrane conductance regulator (CFTR) gene testing also increases the likelihood that a negative report is truly negative. When a newborn patient with zero or one detected CFTR mutation has an inconclusive sweat test result, the sweat test should be repeated before ordering additional often unnecessary CFTR gene sequencing. Given the same composite mutation panel test accuracy, a higher proportion of reported test results would be correct during parental screening than when testing at-risk fetuses or symptomatic newborns. Prenatal and newborn screening would be enhanced substantially by medical professionals offering copies of all positive parental and newborn test reports to the parents to share with their relatives. These principles are likely to be applicable to other genetic diseases as the most common mutation frequencies are reported.

Newborn screening for cystic fibrosis

Newborn screening for cystic fibrosis (CF) was considered over 3 decades ago in 1970; however, the technology did not exist then for an accurate neonatal screening test. With the development of immunoreactive trypsinogen analysis, alone or coupled with DNA mutation analysis, the means were developed for CF newborn screening. Studies have demonstrated benefits of newborn screening in the areas of nutrition, cognitive function, pulmonary function, and survival.

Guidelines for implementation of cystic fibrosis newborn screening programs: Cystic Fibrosis Foundation workshop report

Newborn screening for cystic fibrosis offers the opportunity for early intervention and improved outcomes. This summary, resulting from a workshop sponsored by the Cystic Fibrosis Foundation to facilitate implementation of widespread high quality cystic fibrosis newborn screening, outlines the steps necessary for success based on the experience of existing programs. Planning should begin with a workgroup composed of those who will be responsible for the success of the local program, typically including the state newborn screening program director and cystic fibrosis care center directors. The workgroup must develop a screening algorithm based on program resources and goals including mechanisms available for sample collection, regional demographics, the spectrum of cystic fibrosis disease to be detected, and acceptable failure rates of the screen. The workgroup must also ensure that all necessary guidelines and resources for screening, diagnosis, and care be in place prior to cystic fibrosis newborn screening implementation. These include educational materials for parents and primary care providers; systems for screening and for providing diagnostic testing and counseling for screen-positive infants and their families; and protocols for care of this unique population. This summary explores the benefits and risks of various screening algorithms, including complex situations that can occur involving unclear diagnostic results, and provides guidelines and sample materials for state newborn screening programs to develop and implement high quality screening for cystic fibrosis.

A survey of newborn screening for cystic fibrosis in Europe

BACKGROUND

Cystic fibrosis (CF) is a recessively inherited condition caused by mutation of the CFTR gene. Newborn infants with CF have raised levels of immuno-reactive trypsinogen (IRT) in their serum. Measurement of IRT in the first week of life has enabled CF to be incorporated into existing newborn screening (NBS) blood spot protocols. However, IRT is not a specific test for CF and NBS therefore requires a further tier of tests to avoid unnecessary referral for diagnostic testing. Following identification of the CFTR gene, DNA analysis for common CF-associated mutations has been increasingly used as a second tier test. The aim of this study was to survey the current practice of CF NBS programmes in Europe.

METHOD

A questionnaire was sent to 26 regional and national CF NBS programmes in Europe.

RESULTS

All programmes responded. The programmes varied in number of infants screened and in the protocols employed, ranging from sweat testing all infants with a raised first IRT to protocols with up to four tiers of testing. Three different assays for IRT were used; in the majority (24) this was a commercially available kit (Delfia). A number of programmes employed a second IRT measurement in the 4th week of life (as the IRT is more specific at this point). Nineteen programmes used DNA analysis for common CFTR mutations on samples with a raised first IRT. Three programmes used a second IRT measurement on infants with just one recognised mutation to reduce the number of infants referred for sweat testing. Referral to clinical services was prompt and diagnosis was confirmed by sweat testing, even in infants with two recognised mutations in most programmes. Subsequent clinical pathways were less uniform. Multivariate analysis demonstrated a relationship between the age of diagnosis and the timing of the first IRT. More sweat tests were undertaken if the first IRT was earlier and the diagnosis was later.

CONCLUSIONS

Annually these programmes screen approximately 1,600,000 newborns for CF and over 400 affected infants are recognised. The findings of this survey will guide the development of European evidence based guidelines and may help new regions or nations in the development and implementation of NBS for cystic fibrosis.