Variation of sweat sodium and chloride with age in cystic fibrosis and normal populations: further investigations in equivocal cases

SLIDE-Novel Approach to Apocrine Sweat Sampling for Lipid Profiling in Healthy Individuals

We designed a concept of 3D-printed attachment with porous glass filter disks—SLIDE (Sweat sampLIng DevicE) for easy sampling of apocrine sweat. By applying advanced mass spectrometry coupled with the liquid chromatography technique, the complex lipid profiles were measured to evaluate the reproducibility and robustness of this novel approach. Moreover, our in-depth statistical evaluation of the data provided an insight into the potential use of apocrine sweat as a novel and diagnostically relevant biofluid for clinical analyses. Data transformation using probabilistic quotient normalization (PQN) significantly improved the analytical characteristics and overcame the ‘sample dilution issue’ of the sampling. The lipidomic content of apocrine sweat from healthy subjects was described in terms of identification and quantitation. A total of 240 lipids across 15 classes were identified. The lipid concentrations varied from 10⁻¹⁰ to 10⁻⁴ mol/L. The most numerous class of lipids were ceramides (n = 61), while the free fatty acids were the most abundant ones (average concentrations of 10⁻⁵ mol/L). The main advantages of apocrine sweat microsampling include: (a) the non-invasiveness of the procedure and (b) the unique feature of apocrine sweat, reflecting metabolome and lipidome of the intracellular space and plasmatic membranes. The SLIDE application as a sampling technique of apocrine sweat brings a promising alternative, including various possibilities in modern clinical practice.

Females with cystic fibrosis have a larger decrease in sweat chloride in response to lumacaftor/ivacaftor compared to males

AIM

To explore which patient-related factors influence sweat test response to CFTR modulators, as well as examining the correlation between the sweat chloride response and ppFEV₁ or BMI response, using systematically collected real-life clinical data.

METHODS

160 CF patients were identified who had used lumacaftor/ivacaftor for at least six months. Of these patients, age, sweat chloride levels, ppFEV₁ weight and BMI at the start of treatment and after 6 months were collected retrospectively. Pearson and Spearman tests were performed to assess correlations.

RESULTS

Females compared to males in this group showed a larger response in sweat chloride (mean difference 10.6 mmol/l, 95% CI: 5.7-15.4) and BMI (mean difference 0.27 kg/m², 95% CI: 0.01-0.54). A modest but significant correlation was found between patient weight and sweat chloride response (Pearson R = 0.244, p = 0.001), which diminished upon correction for the other factors. The correlation between sex and sweat chloride response remained; R = 0.253, p = 0.001. Sweat chloride response did not correlate with ppFEV₁ change or BMI change at 6 months after start of therapy.

CONCLUSION

Sweat chloride response is larger in females compared to males, which also explains the negative correlation of weight with the response in sweat chloride concentration after start of lumacaftor/ivacaftor. Sweat chloride response does not correlate with the responses in ppFEV₁ and BMI. This information may help the interpretation of sweat test results acquired for the follow up and evaluation of CFTR modulating treatments, and warrants further investigation into the underlying mechanisms of sex differences in response to CFTR modulators.

Hematological and biochemical reference values of Asian house shrews (Suncus murinus) in Bangladesh

Background and Aim:

Determining reference values for hematological and biochemical parameters of Asian house shrew (Suncus murinus) is important for wildlife research to protect human health in surrounding communities. This study aimed to establish the reference values for selected hematology and serum clinical chemistry analyses that may contribute to research on shrew in future.

Materials and Methods:

Blood samples (n=51) were collected from shrews between July and December 2015, Bangladesh, to estimate the levels of hemoglobin (Hb), packed cell volume (PCV), total leukocyte count (TLC), total erythrocyte count (TEC), lymphocyte, monocyte, neutrophil, eosinophil, basophil, calcium, phosphorus (P), sodium (Na), chloride (Cl), urea, glucose, total protein (TP), creatinine, and alanine transaminase (ALT).

Results:

Although the values did not differ significantly among sexes, age was found to be a significant factor. Hb, PCV, TEC, glucose, and P were higher in males; eosinophil, Na, Cl, TP, and ALT were higher among females. Adults had significantly greater urea and glucose (p<0.05) while juveniles had insignificantly higher values for TLC, PCV, neutrophil, P, and TP.

Conclusion:

This study provides the first reference values for this species in Bangladesh and can be used to guide wildlife research studies.

Performance Evaluation of a New Coulometric Endpoint Method in Sweat Testing and Its Comparison With Classic Gibson&Cooke and Chloridometer Methods in Cystic Fibrosis

Background: The objective of the study was to assess the diagnostic efficacy of the coulometric endpoint method and compare it with classic Gibson&Cooke and chloridometer methods. Methods: This study is a prospective clinical study comparing two conventional sweat testing methods with the coulometric endpoint method in previously diagnosed cystic fibrosis (CF) patients and a non-CF control group. All individuals underwent two simultaneous sweat collections. One sample of sweat, collected by the CFΔ collector coil system, was analyzed by two methods: the titrimetric Cl^- measurement (Sherwood® Chloridometer 926S, Sherwood Scientific Ltd., Cambridge, UK) and the coulometric endpoint method (CF Δ Collection System®, UTSAT/Turkey); the second sample was collected from the other forearm by the Gibson&Cooke method and the collected sweat was analyzed by manual titration in accordance with the Schales&Schales method. Within-run and between-run imprecisions were evaluated via Cl^- concentrations of 40, 70, and 130 mmol/L samples. Results: One hundred and seventy (60 CF and 110 controls) subjects were included in the study. All three sweat test methods discriminated CF subjects from the healthy individuals. The mean difference between the coulometric endpoint and titrimetric Cl^- measurement methods was -1.5 mmol/L, (95% confidence limits of agreement, ranging from -8.9 to 15.9 mmol/L); the mean difference between manual titration vs. coulometric endpoint methods was 12.8 mmol/L, (95% confidence limits of agreement ranging from -9.7 to 45.3 mmol/L) and the mean difference between the manual titration and titrimetric Cl^- measurement methods was 11.3 mmol/L, (95% confidence limits of agreement ranging from -7.8 to 40.5 mmol/L) based on a Bland-Altman analysis. In the Receiver operating characteristic (ROC) analysis, made on the basis that Cl^- concentration values < 40 mmol/L exclude the CF diagnosis, the coulometric endpoint method resulted in 96.7% sensitivity and 100% specificity for a cut-off value of 58.5 mmol/L (AUC: 0.994; 95% CI = 0.986-1.000; p < 0.001). Conclusions: The coulometric endpoint method can be as reliable as quantitative sweat Cl^- analysis and may be considered as a definitive diagnostic tool for CF.

Proteomic Profiling of Sweat Exosome Suggests its Involvement in Skin Immunity

Healthy human skin sustains an effective immune defense mechanism, formed by a complex physical and chemical epidermal barrier that coordinates with different cellular components of the skin immune system. However, the mechanism by which skin cells regulate local immune homeostasis in health and disease contexts is not well known. To investigate whether exosomes exist in sweat, sweat samples from healthy individuals were collected after aerobic exercise. Sweat exosome was isolated via differential ultracentrifugation, observed under transmission electron microscopy, measured by dynamic light scattering, and confirmed by immunoblot. Further, shotgun liquid chromatography (LC)-mass spectrometry (MS)/MS analysis was conducted to investigate the proteomic profiling of sweat exosome. Secreted exosome was detected in human sweat. A total of 1,062 proteins were identified in sweat exosome, including 997 different proteins compared with sweat proteomics and 896 unique proteins compared with urine, saliva, and plasma exosomes. Diverse antimicrobial peptides and immunological factors were found in sweat exosome, suggesting the involvement of exosome in skin immunity. This study provides direct evidence that secreted exosomes exist in human sweat. The proteomic profiling of sweat exosome provides insight into sweat features and the potential physiological significance of exosomes in immune homeostasis.

Is sweat chloride predictive of severity of cystic fibrosis lung disease assessed by chest computed tomography?

BACKGROUND

Cystic Fibrosis (CF) lung disease is characterized by a marked heterogeneity. Sweat chloride-level is a functional marker of the CF Transmembrane Regulator (CFTR) protein and could be an important predictor of later disease severity.

METHODS

In this retrospective analysis children from the Rotterdam CF clinic with available sweat chloride level at diagnosis and at least one routine spirometry-controlled volumetric chest CT scan in follow-up were included. CT scans were scored using the CF-CT scoring system (% of maximum). Associations between sweat chloride-levels and CF-CT scores were calculated using linear regression models, adjusting for age at sweat test and age at follow-up. Because structural lung damage develops over the course of many years, effect modification by the age at follow-up CT-scan was tested for by age-stratification.

RESULTS

In 59 children (30 male) sweat chloride was measured at diagnosis (median age 0.5 years, range 0-13) and later chest CT performed (median age 14 years, range 6-18). Sweat chloride was associated with significantly higher CT-CT total score, bronchiectasis score, and mucus plugging score. Stratification for age at follow-up in tertiles showed this association remained only in the oldest age group (range 15-18 years). In that subgroup associations were found with all but one of the CF-CT subscores, as well as with all tested lung functions parameters.

CONCLUSION

Sweat chloride-level is a significant predictor of CF lung disease severity as determined by chest CT and lung function. This association could only be demonstrated in children with follow-up to age 15 years and above.

Sources of Variation in Sweat Chloride Measurements in Cystic Fibrosis

RATIONALE

Expanding the use of cystic fibrosis transmembrane conductance regulator (CFTR) potentiators and correctors for the treatment of cystic fibrosis (CF) requires precise and accurate biomarkers. Sweat chloride concentration provides an in vivo assessment of CFTR function, but it is unknown the degree to which CFTR mutations account for sweat chloride variation.

OBJECTIVES

To estimate potential sources of variation for sweat chloride measurements, including demographic factors, testing variability, recording biases, and CFTR genotype itself.

METHODS

A total of 2,639 sweat chloride measurements were obtained in 1,761 twins/siblings from the CF Twin-Sibling Study, French CF Modifier Gene Study, and Canadian Consortium for Genetic Studies. Variance component estimation was performed by nested mixed modeling.

MEASUREMENTS AND MAIN RESULTS

Across the tested CF population as a whole, CFTR gene mutations were found to be the primary determinant of sweat chloride variability (56.1% of variation) with contributions from variation over time (e.g., factors related to testing on different days; 13.8%), environmental factors (e.g., climate, family diet; 13.5%), other residual factors (e.g., test variability; 9.9%), and unique individual factors (e.g., modifier genes, unique exposures; 6.8%) (likelihood ratio test, P < 0.001). Twin analysis suggested that modifier genes did not play a significant role because the heritability estimate was negligible (H2 = 0; 95% confidence interval, 0.0-0.35). For an individual with CF, variation in sweat chloride was primarily caused by variation over time (58.1%) with the remainder attributable to residual/random factors (41.9%).

CONCLUSIONS

Variation in the CFTR gene is the predominant cause of sweat chloride variation; most of the non-CFTR variation is caused by testing variability and unique environmental factors. If test precision and accuracy can be improved, sweat chloride measurement could be a valuable biomarker for assessing response to therapies directed at mutant CFTR.

Human sweat metabolomics for lung cancer screening

Sweat is one of the less employed biofluids for discovery of markers in spite of its increased application in medicine for detection of drugs or for diagnostic of cystic fibrosis. In this research, human sweat was used as clinical sample to develop a screening tool for lung cancer, which is the carcinogenic disease with the highest mortality rate owing to the advanced stage at which it is usually detected. In this context, a method based on the metabolite analysis of sweat to discriminate between patients with lung cancer versus smokers as control individuals is proposed. The capability of the metabolites identified in sweat to discriminate between both groups of individuals was studied and, among them, a trisaccharide phosphate presented the best independent performance in terms of the specificity/sensitivity pair (80 and 72.7%, respectively). Additionally, two panels of metabolites were configured using the PanelomiX tool as an attempt to reduce false negatives (at least 80% specificity) and false positives (at least 80% sensitivity). The first panel (80% specificity and 69% sensitivity) was composed by suberic acid, a tetrahexose, and a trihexose, while the second panel (69% specificity and 80% sensitivity) included nonanedioic acid, a trihexose, and the monoglyceride MG(22:2). Thus, the combination of the five metabolites led to a single panel providing 80% specificity and 79% sensitivity, reducing the false positive and negative rates to almost 20%. The method was validated by estimation of within-day and between-days variability of the quantitative analysis of the five metabolites.

Sixty-five years since the New York heat wave: advances in sweat testing for cystic fibrosis

The sweat test remains important as a diagnostic test for cystic fibrosis (CF) and has contributed greatly to our understanding of CF as a disease of epithelial electrolyte transport. The standardization of the sweat test, by Gibson and Cooke [Gibson and Cooke (1959) Pediatrics 1959;23:5], followed observations of excessive dehydration amongst patients with CF and confirmed the utility as a diagnostic test. Quantitative pilocarpine iontophoresis remains the gold standard for sweat induction, but there are a number of collection and analytical methods. The pathophysiology of electrolyte transport in sweat was described by Quinton [Quinton (1983) Nature 1983;301:421-422], and this complemented the developments in genetics that discovered the cystic fibrosis transmembrane conductance regulator (CFTR), an epithelial-based electrolyte transport protein. Knowledge of CF has since increased rapidly and further developments in sweat testing include: new collection methods, further standardization of the technique with international recommendations and age related reference intervals. More recently, sweat chloride values have been used as proof of effect for the new drugs that activate CFTR. However, there remain issues with adherence to sweat test guidelines in many countries and there are gaps in our knowledge, including reference intervals for some age groups and stability of sweat samples in transport. Furthermore, modern methods of elemental quantification need to be explored as alternatives to the original analytical methods for sweat electrolyte measurement. The purpose of this review is therefore to describe the development of the sweat test and consider future directions.

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.

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.

Diagnosis of cystic fibrosis by sweat testing: age-specific reference intervals

OBJECTIVE

To develop reference intervals (RIs) for sweat chloride and sodium in healthy children, adolescents, and adults.

STUDY DESIGN

Healthy, unrelated subjects aged from 5 to >50 years and subjects who were pancreatic insufficient with cystic fibrosis (CF) were recruited. Sweat collection was performed on all subjects with the Wescor Macroduct system. Sweat electrolytes were analyzed with direct ion selective electrodes. DeltaF508 mutation analysis was performed on the healthy subjects >/=15 years old.

RESULTS

A total of 282 healthy and 40 subjects with CF were included for analysis. There was no overlap of sweat chloride between the group with CF and the group without CF, but there was some overlap of sweat sodium. Sweat chloride increased with age, with the rate of increase slowing progressively to zero after the age of 19 years. The estimated median (95% RI) for sweat chloride were: 5 to 9 years, 13 mmol/L (1-39 mmol/L); 10 to 14 years, 18mmol/L (3-47 mmol/L); 15 to 19 years, 20 mmol/L (3-51mmol/L); and 20+ years 23 mmol/L (5-56mmol/L).

CONCLUSIONS

We have successfully developed the age-related RI for sweat electrolytes, which will be useful for clinicians interpreting sweat test results from children, adolescents, and adults.

Detection of cystic fibrosis transmembrane conductance regulator activity in early-phase clinical trials

Advances in our understanding of cystic fibrosis pathogenesis have led to strategies directed toward treatment of underlying causes of the disease rather than treatments of disease-related symptoms. To expedite evaluation of these emerging therapies, early-phase clinical trials require extension of in vivo cystic fibrosis transmembrane conductance regulator (CFTR)-detecting assays to multicenter trial formats, including nasal potential difference and sweat chloride measurements. Both of these techniques can be used to fulfill diagnostic criteria for the disease, and can discriminate various levels of CFTR function. Full realization of these assays in multicenter clinical trials requires identification of sources of nonbiological intra- and intersite variability, and careful attention to study design and statistical analysis of study-generated data. In this review, we discuss several issues important to the performance of these assays, including efforts to identify and address aspects that can contribute to inconsistent and/or potentially erroneous results. Adjunctive means of detecting CFTR including mRNA expression, immunocytochemical localization, and other methods are also discussed. Recommendations are presented to advance our understanding of these biomarkers and to improve their capacity to predict cystic fibrosis outcomes.

Sweat testing for cystic fibrosis: A review of New Zealand laboratories

BACKGROUND

Evolving diagnostic criteria for cystic fibrosis, broadening of the populations being tested and the need to interpret intermediate sweat test results have imposed a much greater need to standardize the collection and analysis of sweat.

AIM

To identify variations in sweat testing in New Zealand laboratories and compare these with guidelines from the UK and the USA.

METHODS

All laboratories in New Zealand offering sweat testing were identified and data collected from these laboratories by structured questionnaire.

RESULTS

There were no New Zealand laboratories that conformed to either set of guidelines. Inconsistencies were observed in minimum sweat quantities, the nature of the iontophoresis solution, the sweat electrolytes analysed, quoted reference ranges and recommendations made as a consequence of the result.

CONCLUSIONS

Conformity to the guidelines would help to minimize variation in sweat testing in New Zealand. Performance of a sufficient number of tests to maintain expertise is critical, but geographical constraints make patient travel to distant centres difficult in a small, scattered population. A possible solution, where numbers permit, may be the collection of sweat locally, with referral to a major laboratory for analysis. This is only possible with adequate training in collection and follow-up audit of the sweat testing procedure both in the collection and in the analytical phase.

Diagnosis of cystic fibrosis after newborn screening: the Australasian experience--twenty years and five million babies later: a consensus statement from the Australasian Paediatric Respiratory Group

Newborn screening for cystic fibrosis has been used in Australia and New Zealand for over 20 years. In that time, considerable experience has been developed regarding the early diagnosis of cystic fibrosis after newborn screening. To date, there has not been a consensus on the process of screening and clinical evaluation leading to the diagnosis of cystic fibrosis in infants, many of whom are not symptomatic at time of notification of the screening result. The aim of this paper is to provide some consensus on the important issues of a cystic fibrosis diagnosis arising from newborn screening, based on the experience gained in Australia and New Zealand over the last 20 years.

Musculoskeletal manifestations in cystic fibrosis

Although bone and joint manifestations are common in children with cystic fibrosis (CF), they have received little attention in adults. As compared to healthy individuals, bone mineral density is low, even with calcium intakes greater than 1500 mg/d. Nevertheless, calcium and phosphate levels in blood and urine are often normal, and vitamin D levels vary. Short stature with a low body mass index and central hypogonadism are the rule in these patients. Fractures and kyphosis are often reported. CF arthropathy occurs in 2-8.5% of patients. Arthritis develops, and there may be skin eruptions. Non-steroidal antiinflammatory drug therapy is effective. Hypertrophic osteoarthropathy associated with respiratory failure is present in 2-7% of patients. Rheumatoid arthritis, spondyloarthropathies, sarcoidosis, and amyloidosis have been reported in association with CF. Knee pain due to patellofemoral syndrome, quinolone-induced arthropathy, and mechanical back pain have been described. Rheumatoid factor titers are higher than in healthy controls, particularly in patients with episodic arthritis. No data are available on antiperinuclear factor or antikeratin antibody titers. Tests for antinuclear antibody are usually negative. Circulating immune complex levels and antibodies to heat shock proteins may be elevated. Antineutrophil cytoplasmic antibody of the bactericidal/permeability-increasing protein (BPI) or azurocidin (AZ) type has been reported, often in high titers (up to 40%).

Mutations of the cystic fibrosis gene and intermediate sweat chloride levels in children

The incidence of mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene in children with intermediate sweat chloride levels is unknown. The results of 2,349 sweat tests performed at two Belgian university hospitals were reviewed. Intermediate chloride concentrations were observed in 98 subjects (4.2%), 68 being younger than 18 years of age. Forty-three children could be traced and their parents agreed to take part in the study. Exhaustive analysis of the CFTR gene disclosed a total of 24 putative mutations (27.9%). Three subjects were found to carry only one CFTR mutation, whereas 10 harbored one mutation on both CFTR genes. These 10 children were investigated in detail. At the time of writing, the mean age (+/-SD) of this group is 8.9 years (+/-4.2 years). Nine children are pancreatic sufficient. Three have been asymptomatic for more than two years, whereas the others display, to different degrees, clinical features suggestive of CF. The sweat chloride concentration is slightly higher in this group (39.4 +/- 5.4 mM) than in subjects without CFTR mutation (35.2 +/- 4.4 mM, p < 0.05). The nasal potential difference was abnormal in five of the nine subjects tested. In this study, 23% of children displaying intermediate sweat chloride levels were found to carry a putative mutation on both CFTR genes.

Increased prevalence of mutations in the cystic fibrosis transmembrane conductance regulator in children with chronic rhinosinusitis

OBJECTIVE

Chronic rhinosinusitis results in significant morbidity in the pediatric population; however, no predisposing factor is found in many cases. Cystic fibrosis (CF) is a recognized cause of chronic rhinosinusitis. Although the carrier frequency for CF ranges from 3% to 4% in the general white population, the prevalence of mutations in the CF transmembrane conductance regulator (CFTR) among children with chronic rhinosinusitis is unknown. Our objective was to study the frequency of CFTR mutations among children with chronic rhinosinusitis.

METHODS

Fifty-eight white children who were from the St Louis metropolitan area and had chronic rhinosinusitis, none of whom satisfied diagnostic criteria for CF, underwent sweat testing and genotyping for CFTR mutations using an assay that detects 90% of mutations seen in this ethnic group.

RESULTS

Seven of the 58 patients (12.1%) tested harbored CFTR mutations as compared with the expected rate of 3% to 4% in this ethnic group. Five patients had the DeltaF508, 1 had the R117H, and 1 had the I148T mutation. Only 1 of the 7 children had a borderline abnormal sweat test. Two of the 58 patients experienced recurrent Pseudomonas aeruginosa rhinosinusitis, and both were DeltaF508 heterozygotes. Three other children with no detectable CFTR mutation had borderline elevated sweat-test results. The CFTR intron 8 5T polymorphism was found at a frequency comparable to that reported for the general population.

CONCLUSION

There is an increased occurrence of CFTR mutations in children who have chronic rhinosinusitis and do not meet diagnostic criteria for CF, usually in the setting of a normal sweat chloride. These results suggest a role for CFTR mutations in predisposition to chronic rhinosinusitis.

Sweat testing following newborn screening for cystic fibrosis

Sweat testing remains the "gold standard" for the diagnosis of cystic fibrosis (CF) and is a critical component of newborn screening programs. We retrospectively reviewed sweat test results reported to a neonatal screening program for CF with respect to completeness of reported results and the values recorded for sweat chloride (Cl(-)) and sodium (Na(+)) concentrations and the Cl(-):Na(+) ratio in screened infants. Thirty-nine of 85 DeltaF508 homozygous (DeltaF508/DeltaF508) and 270 of 274 DeltaF508 heterozygous (DeltaF508/-) infants had sweat tests reported to the screening program. Of those, 30 and 213 sweat test reports, respectively, were complete, i.e., sweat weight, sweat chloride, and sodium were reported. Three centers accounted for 37 of 68 (54%) incomplete results, and 4 centers performed 4 or less post-screening sweat tests in the study period. There were 6 DeltaF508 heterozygous infants with sweat Cl(-) concentrations of 40-60 mmol/L and 4 had CF confirmed by additional genotyping (n = 2) or clinical and repeat sweat Cl results (n = 2). Forty-one percent of DeltaF508/-infants with sweat Cl(-) <40 mmol/L had Cl:Na >1. We conclude that the reporting of incomplete sweat tests is common following newborn screening for CF. Infants with sweat Cl(-) levels of 40-60 mmol/L require further investigation and review, but they almost certainly have CF. The Cl(-):Na(+) ratio does not appear useful in establishing a diagnosis of CF in infants.

Indirect measurements of sweat electrolyte concentration in the laboratory diagnosis of cystic fibrosis

AIM

To investigate whether analytical methods based on the colligative physical chemical properties of ions or solutes in sweat are less effective than the specific measurement of electrolytes in the diagnosis of cystic fibrosis (CF).

METHODS

A single sweat sample was collected (Macroduct) from each of 211 infants and children, of whom 57 had CF, for the measurement of sodium, chloride, osmolality, and conductivity.

RESULTS

The ranges within which CF and non-CF individual values overlapped (equivocal ranges), were wider for sodium and osmolality measurement than for chloride or conductivity. Neither of the latter two measurements provided a discriminatory advantage over the other. The utilisation of broadly based age related ranges for non-CF control subjects served to improve the discriminatory power of all four measurements to an extent that, in this cohort, both chloride and conductivity provided complete discrimination.

CONCLUSION

Sweat conductivity is as effective as chloride measurement in the laboratory diagnosis of CF.

[Type Ib pseudohypoaldosteronism: clinical aspects and nosological problems. Apropos of 3 cases]

BACKGROUND

Type Ib pseudohypoaldosteronism is a congenital disorder characterized in the newborn by salt loss caused by multiple end-organ resistance to aldosterone. An autosomal recessive mode of inheritance has been reported. Its particularity is the spontaneous improvement by 18 months to 2 years, due to an improved tubular response of the kidneys to mineralocorticoids, or earlier when given salt supplements once the diagnosis is made.

OBSERVATIONS

We observed three children with this disease, which was revealed by day 8 to day 15 of life; one of these presented respiratory symptoms identical to those of cystic fibrosis, and another one an apparently chance association with a rod myopathy.

CONCLUSION

Recent findings in the literature demonstrate the molecular aspects of pseudohypoaldosteronism and lead to an interesting comparison with cystic fibrosis by explaining their similar physiopathology through the activity of epithelial sodium channels.

P67L: a cystic fibrosis allele with mild effects found at high frequency in the Scottish population

Only three mutant cystic fibrosis (CF) alleles have to date been established as conferring a dominant mild effect on affected subjects who are compound heterozygotes. We now add a fourth, P67L, which occurs on about 1.4% of Scottish CF chromosomes. Among 13 patients (12 unrelated) with this allele, the average age at diagnosis was 22.5 +/- 11.3 years. None of the cases had consistently raised sweat chloride concentrations, the average value being 57 +/- 9 mmol/l; 77% of the patients were pancreatic sufficient. When compared to three other established mild CF alleles, R117H, A455E, and 3849 + 10kb C-T, a compound heterozygote for P67L has minimal disease and clinical suspicions are unlikely to be confirmed other than by DNA typing.

Sweat testing for the diagnosis of cystic fibrosis: practical considerations

Most pediatricians eventually encounter a patient with a clinical presentation that warrants the consideration of a sweat test to rule out of confirm the diagnosis of cystic fibrosis. This article discusses, in a series of questions and answers, the currently available sweat testing methods and describes the various methods' reliability, limitations, and frequency of use. In addition, sweat testing utilization and the interpretation and evaluation of test results are discussed so that the clinician can critically analyze the laboratory data.

Pulmonary function and clinical observations in men with congenital bilateral absence of the vas deferens

Congenital bilateral absence of the vas deferens (CBAVD) was once thought to be a distinct clinical entity, but genetic similarities in men with cystic fibrosis (CF) and CBAVD are described increasingly. We evaluated the clinical status, growth and nutritional state, and respiratory function of 18 men with CBAVD to determine whether these men with different CF transmembrane regulator (CFTR) genotypes may have clinical evidence of mild CF. Following a thorough history and examination, pulmonary function tests, sweat test, and renal ultrasound were performed. Genetic evaluation for 50 known CF mutations, screening for private mutations (single-strand conformational polymorphism and direct sequencing), and assay of the length of the polypyrimidine tract in the splice site acceptor of intron 8 was performed. A history of pulmonary disease was present in three, and an additional man had some features suggestive of malabsorption. Results of general physical examination and anthropomorphic measurements were unremarkable in all patients, with a mean (SD) body mass index of 26 (3). Pulmonary function tests of large and small airway function as well as lung volumes were normal in all except one whose results were consistent with moderate asthma. Five men were compound heterozygotes for CFTR mutations, four of whom had positive sweat tests (sweat chloride > 60 mEq/L). Twelve men were heterozygotes for CFTR mutations while no mutations were identified in one man. Although putative etiologic factors may suggest that men with CBAVD and CFTR mutations could be considered within the spectrum of clinical CF, the authors suggest that in men with CBAVD without any other clinical features of CF, the diagnosis of CF may not be made.