Sweat test practice in pediatric pulmonology after introduction of cystic fibrosis newborn screening

Cystic fibrosis in low and middle-income countries (LMIC): A view from four different regions of the world

Cystic fibrosis (CF) has been shown to affect people all over the world. While life expectancy for people with CF has increased substantially, CF is still associated with death in infants and young children in many regions, particularly in low and middle-income countries (LMIC). These countries face significant challenges to promote CF diagnosis and improvements to CF care due to financial constraints and a significant burden of other diseases. In this review, we describe the status of CF diagnosis and care in different LMIC settings, from four different parts of the world (Brazil, South Africa, Israel and India). We highlight challenges and opportunities for CF practitioners in LMIC to improve CF care and outcomes. While early CF diagnosis is the key to optimising outcomes, newborn screening may not be feasible for countries with lower CF incidence and higher birth rates, such as India or South Africa. CF therapies and care in LMIC need to be adapted to available resources of these countries. Collaboration initiatives of the global CF community with LMIC may improve CF care in these countries. Most individuals with CF in LMIC are not benefiting from CFTR modulator treatments due to the prohibitive cost of these drugs.

Extensive CFTR sequencing through NGS in Brazilian individuals with cystic fibrosis: unravelling regional discrepancies in the country

BACKGROUND

The Brazilian population has a tri-hybrid composition with a high degree of ethnic admixture. We hypothesized that Brazilian individuals with CF from different Brazilian regions have a specific distribution of CFTR variants.

METHODS

Individuals with CF with data available in the Patient Registry and without an established genotype were submitted to CFTR sequencing by Next Generation Sequencing (NGS) methodology, and results were anonymously incorporated to the Registry Database. Genotyping results were expressed as 'positive', 'inconclusive' or 'negative'. Logistic regression models were performed to investigate the association between demographic/clinical variables and genotyping results. Mediation analysis was conducted to estimate direct and indirect effects of Brazilian region on a binary positive genotyping response.

RESULTS

In October 2017, data from 4,654 individuals with CF were available, and 3,104(66.7%) of them had a genotyping result. A total of 236 variants (114 new variants) were identified, with F508del identified in 46% of the alleles tested. Genotyping revealed 2,002(64.5%) individuals positive, 757(24.4%) inconclusive and 345(11.1%) negative. Distribution of genotype categories was markedly different across Brazilian Regions, with greater proportions of negative individuals in the North (45%) and Northeast (26%) regions. Newborn screening (CF-NBS) and age at diagnosis were identified as mediators of the effect of Brazilian region on a positive genotyping result.

CONCLUSIONS

This large initiative of CFTR genotyping showed significant regional discrepancies in Brazil, probably related to socio-economic conditions, lack of adequate CF-NBS and poor access to reliable sweat testing. These results may be useful to indicate Regions where CF care demands more attention.

Sweat chloride quantification using capillary electrophoresis

Background

Cystic fibrosis (CF) is the less rare and severe genetic disease among the European population. Biochemical diagnosis of CF is based on the demonstration of increased chloride concentration in sweat samples, obtained during the sweat test (ST). WynSep developed a capillary electrophoresis with contactless conductivity detection (CE-C4D) able to measure sweat chloride with a low sample volume. We evaluated the clinical feasibility of this device in a cohort of patients suspected of CF, in comparison with the common coulometric method (ChloroChek chloridometer).

Methods

We determined sweat chloride concentration of 65 samples from patients referred to our institution to undergo a sweat test. Each sample was submitted to coulometric method first, then WynSep-CE, with or without internal standard (IS) subject to sufficient volume sample.

Results

A total of 53 samples were analysed by both coulometric and WynSep-CE (using IS) methods. The method validation showed comparable analytical performances for both methods; no false positive or false negative was recorded. The two methods showed a high correlation (r = 0.993, p < 0.001) and a close agreement was demonstrated by two different statistical tests (Bland-Altman and Passing-Bablok).

Conclusions

WynSep-CE is an accurate, fast, easy-to-use and an appropriate method for CF diagnosis.

Newborn Screening Saves Lives but Cannot Replace the Need for Clinical Vigilance

Newborn screening for cystic fibrosis (CF) enables early diagnosis and treatment leading to improved health outcomes for patients with CF. Although the sensitivity of newborn screening is high, false-negative results can still occur which can be misleading if clinicians are not aware of the clinical presentation of CF. We present a case of a young male with negative newborn screen diagnosed for CF. He was diagnosed at 3 years of age despite having symptoms indicative of CF since infancy. The delayed diagnosis resulted in diffuse lung damage and poor growth.

Real life practice of sweat testing in Europe

Evidence based guidelines exist for sweat testing, which remains a key component of a diagnosis of cystic fibrosis (CF), especially following newborn bloodspot screening (NBS). There are emerging challenges with respect to maintaining a valid sweat test service, notably a smaller number of sweat tests ordered in regions with established NBS programmes where Pediatricians refer less children for sweat testing, younger patients and equipment becoming obsolete. The ECFS Diagnostic Network Working Group has undertaken a comprehensive survey to better define sweat test practice across Europe. The survey was completed by 136 European respondents representing a CF center or laboratory providing a sweat test service (65% from regions with NBS for CF). There was considerable variance in practice, often not consistent with guidelines. In particular collection of sweat from two sites was rarely reported in European centres in contrast to US guidelines. There was a range of different references quoted for cut-off for both a positive and intermediate test. Most responses suggest cost is becoming an increasing issue and is not sufficiently reimbursed. This work will inform best practice guidelines and resources to sustain and improve sweat testing in Europe.

Thirty Years of Sweat Chloride Testing at One Referral Center

OBJECTIVE

To conduct a descriptive analysis of the sweat test (ST), associating ST results with epidemiological data, CFTR (cystic fibrosis transmembrane conductance regulator) mutations and reasons to indicate the ST, as well as correlating sweat sodium and sweat chloride concentrations in subjects.

METHODS

Retrospective survey and descriptive analysis of 5,721 ST at a university referral center.

RESULTS

The inclusion of the subjects was based on clinical data related with cystic fibrosis (CF) phenotype. The samples were grouped by (i) sweat chloride concentrations (mEq/L): <30: 3,249/5,277 (61.6%); ≥30 to <60: 1,326/5,277 (25.1%); ≥60: 702/5,277 (13.3%) and (ii) age: (Group A--GA) 0 to <6 months; (Group B--GB) ≥6 months to <18 years; (Group C--GC) ≥18 years. Digestive symptoms showed higher prevalence ratio for the CF diagnosis as well as association between younger age and higher values of sweat chloride, sweat sodium, and chloride/sodium ratio. The indication of ST due to respiratory symptoms was higher in GB and associated with greater age, lower values of sweat chloride, sweat sodium, and chloride/sodium ratio. There was higher prevalence of ST with sweat chloride levels <30 mEq/L in GB, ≥60 mEq/L in GC, and with borderline level in GB. There was positive correlation between sweat sodium and sweat chloride. Sweat chloride/sweat sodium and sweat sodium-sweat chloride indexes showed association with sex, reason for ST indication, and CFTR mutations. Sex alters some values presented in the ST. The number of ST/year performed before and after the newborn screening implementation was the same; however, we observed a higher number of borderlines values. A wide spectrum of CFTR mutation was found. Severe CFTR mutations and F508del/F508del genotype were associated with highest probability of ST chloride levels ≥60 mEq/L, and the absence of CFTR mutations identified was associated with borderline ST and respiratory symptoms.

CONCLUSIONS

ST data showed wide variability dependent on age, sex, reason for examination indication, CFTR mutations, and weight of the collected sweat sample. Sweat sodium concentration is directly correlated with sweat chloride levels and it could be used as a quality parameter.