Diagnostic Test For Cystic Fibrosis Research Articles

P366 Developing an in-house and integrated sweat testing service for the routine management of adults with cystic fibrosis

Since 1959, the sweat test has become an essential diagnostic test for cystic fibrosis (CF). In 2012, the CFTR potentiator, ivacaftor became available on the National Health Service (NHS) in England. Commissioning guidance advised that all eligible patients should have a sweat test within 6 months of starting treatment and then at least annually. Historically at Leeds Teaching Hospitals NHS Trust, sweat tests were performed by the biomedical team.

Sweat testing in the modern era: A national survey of sweat testing practice in the Republic of Ireland

BackgroundThe sweat test has been the "gold standard" diagnostic test for cystic fibrosis for more than 40 years. We hypothesized that there would be a change in the pattern of sweat testing in Ireland since the introduction of cystic fibrosis newborn screening in 2011, when practices were last reviewed. This is a follow up survey looking at sweat testing numbers and practices. MethodsA national survey compiled data on sweat collection, conductivity and sweat chloride testing in all hospitals previously identified as performing sweat tests. ResultsAll 13 centres in Ireland performing sweat testing in 2018 responded to the survey (100% return rate). Our results indicate that 1007 sweat tests were performed in 2018 compared to 2555 in 2011, equating to a 61% reduction. Seven out of 13 centres are performing less than 50 sweat tests per year. Nine out of 13 centres (69%) had a sweat test failure rate greater than the recommended allowable rate of ≤ 10%. We detected a trend of sweat testing in patients with an existing diagnosis of CF who had commenced cystic fibrosis transmembrane conductance regulator (CFTR) modulators. ConclusionsThere has been a significant reduction in the number of sweat tests performed in Ireland since the introduction of newborn screening for CF. There remains a lack of standardisation in many aspects of the service ranging from sample collection to reporting of results. We have identified a new trend of sweat testing in the cystic fibrosis transmembrane conductance regulator modulator era.

WS04-6 Development of the Rectal Organoid Morphology Analysis (ROMA) as a diagnostic test for cystic fibrosis

WS04-6 Development of the Rectal Organoid Morphology Analysis (ROMA) as a diagnostic test for cystic fibrosis

WS10.2 Organoids as diagnostic test for cystic fibrosis

WS10.2 Organoids as diagnostic test for cystic fibrosis

The diagnosis of cystic fibrosis

Establishing the diagnosis of cystic fibrosis (CF) is straight forward in the majority of patients: they present with a clear clinical picture (most frequently chronic respiratory symptoms plus malabsorption), the sweat chloride value is>60mmol/L and two known disease causing CFTR mutations are identified. In less than 5% of subjects, mainly those with a milder or limited phenotype, the diagnostic process is more complex, because initial diagnostic test results are inconclusive: sweat chloride concentration in the intermediate range, less than 2 CF causing mutations identified or both. These patients should be referred to expert centers where bioassays of CFTR function like nasal potential difference measurement or intestinal current measurement can be done. Still, in some patients, despite symptoms compatible with CF and some indication of CFTR dysfunction (e.g. only intermediate sweat chloride value), diagnostic criteria are not met (e.g. only 1 CFTR mutation identified). For these subjects, the term CFTR related disorder (CFTR-RD) is used. Patients with disseminated bronchiectasis, congenital bilateral absence of the vas deferens and acute or recurrent pancreatitis may fall in this category. CF has a very wide disease spectrum and increasingly the diagnosis is being made during adult life, mainly in subjects with milder phenotypes. In many countries, nationwide CF newborn screening (NBS) has been introduced. In screen positive babies, the diagnosis of CF must be confirmed by a sweat test demonstrating a sweat chloride concentration above 60mmol/L. To achieve the benefit of NBS, every baby in whom the diagnosis of CF is confirmed must receive immediate follow-up and treatment in a CF reference center. CF NBS is not full proof: some diagnoses will be missed and in some babies the diagnosis cannot be confirmed nor ruled out with certainty. Screening algorithms that include gene sequencing will detect a high number of such babies that are screen positive with an inconclusive diagnosis (CFSPID). Even in 2016, the most reliable and widely available diagnostic test for CF is the measurement of chloride concentration in sweat. The method of choice is sweat induction by pilocarpine iontophoresis, followed by sweat collection on a gauze or filter paper or in a Macroduct coil. Since mutation specific therapies have become available, it is important to identify the mutations responsible for CF in each individual patient.

Sweat conductivity: An accurate diagnostic test for cystic fibrosis?

BackgroundSweat chloride test is the gold standard test for cystic fibrosis (CF) diagnosis. Sweat conductivity is widely used although still considered a screening test. MethodsThis was a prospective, cross-sectional, diagnostic research conducted at the laboratory of the Instituto da Criança of the Hospital das Clínicas, São Paulo, Brazil. Sweat chloride (quantitative pilocarpine iontophoresis) and sweat conductivity tests were simultaneously performed in patients referred for a sweat test between March 2007 and October 2008. Conductivity and chloride cut-off values used to rule out or diagnose CF were <75 and ≥90mmol/L and <60 and ≥60mmol/L, respectively. The ROC curve method was used to calculate the sensitivity, specificity, positive (PPV) and negative predictive value (NPV), as well as the respective 95% confidence intervals and to calculate the area under the curve for both tests. The kappa coefficient was used to evaluate agreement between the tests. ResultsBoth tests were performed in 738 children, and CF was ruled out in 714 subjects; the median sweat chloride and conductivity values were 11 and 25mmol/L in these populations, respectively. Twenty-four patients who had received a diagnosis of CF presented median sweat chloride and conductivity values of 87 and 103mmol/L, respectively. Conductivity values above 90mmol/L had 83.3% sensitivity, 99.7% specificity, 90.9% PPV and 99.4% NPV to diagnose CF. The best conductivity cut-off value to exclude CF was <75mmol/L. Good agreement was observed between the tests (kappa: 0.934). ConclusionsThe sweat conductivity test yielded a high degree of diagnostic accuracy and it showed good agreement with sweat chloride. We suggest that it should play a role as a diagnostic test for CF in the near future.

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.

Nasal potential difference measurements in diagnosis of cystic fibrosis: An international survey

The role of nasal potential difference (NPD) measurement as a diagnostic test for cystic fibrosis (CF) is a subject of global controversy because of the lack of validation studies, clear reference values, and standardized protocols for diagnostic NPD. To determine diagnostic NPD frequency, protocols, interpretation, and rater agreement, we surveyed the 18 NPD centres of the European Cystic Fibrosis Society Diagnostic Network Working Group. Fifteen centres reported performing 373 diagnostic NPDs in 2012. Most use the CFF-TDN-SOP (67%) and the chloride-free + isoproterenol response of the side with the largest response (47%) as diagnostic criteria and use centre-specific reference ranges. Rater agreement for five NPD tracings - in general - was good, but poor in tracings with different responses between the two nostrils. NPD is frequently used as a diagnostic and research tool for CF. Performance is highly standardized, centre-specific reference ranges are established, and rater agreement - in general - is good. Centre-independent diagnostic criteria and reference ranges must be defined by multicentre validation studies to improve standardized interpretation for diagnostic use.

β-Adrenergic Sweat Secretion as a Diagnostic Test for Cystic Fibrosis

β-Adrenergically induced sweat secretion offers an expedient method to assess native cystic fibrosis transmembrane conductance regulator (CFTR) secretory function in vivo. To evaluate the sensitivity, specificity, and reliability of a test based on the activity and secretory function of CFTR in the sweat gland. Primary and validation trials with prospectively ascertained healthy control subjects, obligate heterozygotes, and patients with a CFTR-related disorder and CF (pancreatic sufficient and insufficient). Diagnostic accuracy and reliability of β-adrenergic sweat secretory rates using an evaporimeter was assessed and compared with sweat chloride concentrations. The cholinergically stimulated mean sweat rate did not differ among groups. The mean maximal β-adrenergically stimulated sweat rate in heterozygotes was about half the rate of healthy control subjects, and completely absent in pancreatic-insufficient patients with CF and pancreatic-sufficient patients with CF (P < 0.0001). Subjects with a CFTR-related disorder showed reduced or absent β-adrenergic sweat secretion. The β-adrenergic secretory response demonstrated high diagnostic accuracy (area under a characteristic receiver-operator curve = 0.99; 95% confidence interval, 0.97-1.00) and reliability (intraclass correlation, 0.90; 95% confidence interval, 0.81-0.95). The diagnostic cutoff level for CF, derived from the primary trial, correctly identified all control subjects, heterozygotes, and patients with CF in the validation cohort, whereas concurrent sweat chloride measurements misclassified one heterozygote and five subjects with CF. The cholinergic and β-adrenergic sweat secretion rates were lower in women compared with men (P < 0.001). β-Adrenergic sweat secretion rate determined by evaporimetry is an accurate and reliable technique to assess different levels of CFTR function and to identify patients with CF.

Evaluation of the intestinal current measurement method as a diagnostic test for cystic fibrosis

The sweat test and nasal potential difference measurement are now established tools in the diagnostic work up of cystic fibrosis (CF). Intestinal current measurement (ICM) is under consideration as an aid in the diagnosis of CF especially in young children. The aim of this study is to evaluate the diagnostic reliability of ICM. Rectal biopsies were obtained from three groups: CF patients, controls, and patients who were suspected for CF. ICMs were performed by mounting the rectal biopsy in an Ussing chamber and sequentially adding secretagogues while recording current changes. Twenty-one CF patients (aged 3.0 ± 3.8 years) and 16 controls (aged 15.6 ± 15.1 years) were examined and have remarkably different results (presented as µA/cm(2) ): carbachol 16.3 ± 6.9, histamine 13.2 ± 8.9, and cAMP/forskolin 4.8 ± 4.0 for control group and carbachol -1.5 ± 5.3 (P < 0.0001), histamine -1.5 ± 3.1 (P < 0.0001), and cAMP/forskolin 0.36 ± 0.67 (P < 0.0001) for the CF group. Our suggested reference values are: +5.40, +3.52, +2.19 for carbachol, histamine, and cAMP/forskolin, respectively. The combination parameter (the arithmetic sum of carbachol, histamine, and cAMP/forskolin) of +7.19 differentiates normal from abnormal (ROC curve analysis, area under the curve = 1.00, both sensitivity and specificity are 100%). This statistical model was applied to 71 patients suspected for CF and revealed that 66 patients had normal ICM results (combination >7.19) and five patients had abnormal ICM results (combination <7.19). We have shown that ICM tests may be useful to differentiate between patients suspected to have CF. These results require confirmation so that ICM may be included in diagnostic algorithms.

Interview: Gene therapy for cystic fibrosis: future hopes and milestones

Eric Alton speaks to Sam Rose, Assistant Commissioning Editor Eric Alton is the coordinator of the UK Cystic Fibrosis Gene Therapy Consortium, which brings together the three centers in the UK (Edinburgh and Oxford Universities and Imperial College) focused on this field. Alton is Professor of Gene Therapy and Respiratory Medicine at the National Heart and Lung Institute, Imperial College (London, UK), and Honorary Consultant Physician and Director of the Respiratory Biomedical Research Unit at the Royal Brompton Hospital (London, UK). For over 15 years Alton has moved from inventing a diagnostic test for cystic fibrosis (CF), to developing gene therapy for CF, including two clinical trials. To date, Alton has published more than 130 articles on CF. At the 2011 Medical Futures Innovation Awards; Alton was presented with the Best Translational Research Innovation Award, and the Best Therapeutic Innovation Award (Respiratory). At present, Alton is working towards the first ever clinical trial that will meas...

Nasal potential measurements on the nasal floor and under the inferior turbinate: Does it matter?

Measurement of nasal potential difference (NPD) is increasingly used as diagnostic test for cystic fibrosis (CF) and for in vivo evaluation of treatments aimed at correcting the defective function of the cystic fibrosis transmembrane regulator (CFTR) protein. Several methods are used to measure NPD. This study explores the influence of the site of measurement and compares NPD results obtained on the nasal floor and under the inferior turbinate. NPD was measured in 34 CF, 26 heterozygote, and 61 control subjects. In every subject, measurements were taken simultaneously under the inferior turbinate in one nostril, and on the nasal floor in the other nostril. Criteria for interpretable tracings were predefined. Repeat measurements were done in 57 persons. More interpretable tracings were obtained under the turbinate (120/124) than on the nasal floor (109/124), P = 0.015. Within each subject group, mean values obtained were similar for maximal basal potential, response to amiloride, and total chloride response. Both techniques discriminate well between CF and controls. Repeatability was similar with both methods: mean differences between two measurements approximated zero for most values. Also after correction for different number of interpretable tracings, simulation of sample size calculation for use in CFTR corrective trials was slightly in favor of measurements obtained on the nasal floor. NPD measurements under the inferior turbinate and on the nasal floor have similar discriminative power for diagnostic use. Measurements under the turbinate result in a slightly higher proportion of interpretable tracings but sample size calculation slightly favors the nasal floor method.

Optimizing a cystic fibrosis test for the U.S. population

Objective: To develop a practical diagnostic test for cystic fibrosis (CF) that provides maximal information to a diverse testing population, which includes multiple ethnic groups as well as individuals with a broad range of clinical indications or CF phenotypes.Methods: A molecular assay was developed to test for 70 CF mutations selected from more than 600 previously reported mutations. We tested more than 35,000 individuals for 70 CF mutations. To perform the assay, samples were amplified in two multiplex reactions, immobilized on a solid support, and hybridized with pools of allele-specific oligonucleotide probes. Positive samples were further analyzed by hybridization with individual allele-specific oligonucleotides.Results: We tested over 35,000 individuals for 70 CF mutations. Detection data will be presented for each mutation with respect to indications for testing and ethnic origins. Based on these data, we reevaluated the 70 mutation testing panel and developed an 86 mutation panel more appropriate to the test population. Seven mutations not detected were eliminated, and 23 new mutations were added to improve detection rates in specific groups.Conclusions: A CF mutation panel appropriate to the U.S. test population was optimized. The panel is useful for diagnostic testing—for CF, for infertility with congenital absence of the vas deferens, and for follow-up of abnormal fetal ultrasound examination; or for carrier screening—for individuals with a family history, pregnant couples, couples planning pregnancy, and gamete donors.

Accelerated Red Blood Cell Turnover Can Invalidate the Use of Hemoglobin A1c as a Diagnostic Test for Cystic Fibrosis Related Diabetes

Accelerated Red Blood Cell Turnover Can Invalidate the Use of Hemoglobin A1c as a Diagnostic Test for Cystic Fibrosis Related Diabetes

Faecal immunoreactive lipase: a simple diagnostic test for cystic fibrosis.

The study evaluates faecal immunoreactive lipase (IRL) measurement in spot stool samples as an index of exocrine pancreatic function in patients with cystic fibrosis (CF). Stool samples (211) from 183 healthy volunteers (age range: 2 days-14.2 years) showed a normal log distribution of IRL values with a median concentration of 71.4 micrograms/g (range: 0.53-4160 micrograms/g). In 156 stool samples from 58 patients with proven CF, the median IRL concentration of 0.4 microgram/g (range: 0.003-107 micrograms/g) was significantly lower (P < 0.001) than that of normal controls. In healthy controls, IRL levels were age related with significantly higher levels (P < 0.001) shortly after birth compared to older children. Stimulation of the exocrine pancreas by oral milk feeding resulted in a significant (P < 0.001) increase in a faecal IRL concentration. Faecal IRL concentrations in meconium were very low and of the same magnitude as in patients with CF. Faecal IRL determination had a high diagnostic sensitivity (87%) and excellent diagnostic specificity (97%) in patients with CF. A negative test result (PVneg. 99%) virtually excluded CF under screening conditions.

Normal sweat chloride values do not exclude the diagnosis of cystic fibrosis.

Since its introduction in 1959, the sweat test has remained the "gold standard" diagnostic test for cystic fibrosis (CF). It is apparent that CF encompasses a wide spectrum of disease, from meconium ileus and severe respiratory compromise in infants to the presentation of mild pulmonary symptoms and no evidence of gastrointestinal disease in adults. In patients with lung disease that might otherwise be consistent with CF, normal sweat chloride (Cl-) values have tended to exclude the diagnosis. In this report we describe two patients from two families with the compound heterozygotic CF mutations delta F508/3849 + 10 kb C-->T. These patients had mild manifestations of disease, including clinical pancreatic sufficiency (normal growth without pancreatic enzyme supplementation) and absence of azoospermia. Sweat Cl- values were in the normal range. However, both patients developed bronchiectasis, progressive obstructive lung disease, and colonization with Pseudomonas. The diagnosis of CF was made using nasal transepithelial voltage measurements and genotyping. These cases emphasize the need to maintain a high index of suspicion of CF in atypical cases, and to pursue alternative diagnostic tests to confirm a diagnosis of CF suspected on clinical grounds, despite normal sweat test results.

Normal Sweat Chloride Values Do Not Exclude the Diagnosis of Cystic Fibrosis

Since its introduction in 1959, the sweat test has remained the "gold standard" diagnostic test for cystic fibrosis (CF). It is apparent that CF encompasses a wide spectrum of disease, from meconium ileus and severe respiratory compromise in infants to the presentation of mild pulmonary symptoms and no evidence of gastrointestinal disease in adults. In patients with lung disease that might otherwise be consistent with CF, normal sweat chloride (Cl-) values have tended to exclude the diagnosis. In this report we describe two patients from two families with the compound heterozygotic CF mutations delta F508/3849 + 10 kb C-->T. These patients had mild manifestations of disease, including clinical pancreatic sufficiency (normal growth without pancreatic enzyme supplementation) and absence of azoospermia. Sweat Cl- values were in the normal range. However, both patients developed bronchiectasis, progressive obstructive lung disease, and colonization with Pseudomonas. The diagnosis of CF was made using nasal transepithelial voltage measurements and genotyping. These cases emphasize the need to maintain a high index of suspicion of CF in atypical cases, and to pursue alternative diagnostic tests to confirm a diagnosis of CF suspected on clinical grounds, despite normal sweat test results.

An Unusual Case of Munchausen Syndrome by Proxy

An 11-year-old boy was presented by his father with a long and plausible history of cystic fibrosis. The diagnostic test for cystic fibrosis, the sweat test, was normal and excluded the diagnosis. The medical history was later found to be false, and the child to be well. By definition, the case met the criteria for Munchausen Syndrome by Proxy with fabrication of symptoms on behalf of another in order to deceive medical personnel. Unusual features included the illness chosen, the father as the parent falsifying illness, his failure to pursue unnecessary investigations and treatment, and the ease with which he relinquished the diagnosis of cystic fibrosis.

Nasal potential difference: a clinical diagnostic test for cystic fibrosis

Patients with cystic fibrosis (CF) demonstrate a markedly more negative potential difference (PD) across respiratory epithelia than normal or "diseased" controls. A technique is described for the measurement of nasal PD in both children and adults. 145 non-CF subjects showed a mean PD of -19.0 mV (range -2 to -36) in comparison to 60 patients with cystic fibrosis with mean of -46.0 mV (range -32 to -77). Amongst the latter group those with more severe disease had a more negative PD. Measurement of nasal PD is easily learnt and rapidly performed and may provide an additional means of diagnosis for CF.

Assay of a Urinary CF-Lectin Factor as a Second Diagnostic Test for Cystic Fibrosis

Analysis of urine samples for a lectin-like factor in patients with a diagnosis of cystic fibrosis (CF) revealed that the low molecular weight (MW) factor is present in urine only from such patients and not from heterozygous carriers of the CF gene or from normal controls. The urine fraction containing the factor must be separated from whole urine by a gel filtration column (TSK-20) for the activity to appear. The assay requires addition of an aliquot of normal serum to provide the necessary IgM to which the CF-factor binds, resulting in the lectin-like activity that causes agglutination of mouse erythrocytes. All 22 CF patients tested, who were not receiving intravenous (IV) antibiotics had positive CF-lectin urinary activity, whereas five others receiving IV aminoglycosides were negative. Four patients with a clinical diagnosis of CF, but with normal sweat tests (35-54 mEq/L), all had positive urinary CF-lectin tests. A blind study in which urine samples were shipped from Miami, FL to Sepulveda, CA was completely successful in correctly identifying 11 samples from CF patients as compared with ten from non-CF patients. It was concluded that an assay for urinary CF-lectin factor is specific and reliable for confirming a diagnosis of CF when the sweat test is indeterminate, and when patients have not received recent IV aminoglycosides.