Serum levels of immunoreactive trypsinogen (IRT) are higher in newborns with CF and remain elevated longer compared to newborns who are not affected by the disease.8,9

An elevation of IRT at birth is not specific for CF, as there are healthy newborns that experience a transient elevation of this enzyme. The specificity of elevation of IRT in a single sample is low, so protocols have been developed that use a DNA test in the first neonatal sample (IRT+DNA), the protocol most frequently used in Spain, or that request a second sample for repeat measurement of IRT followed by a DNA test (IRT+IRT+DNA), or a sweat test (Fig. 1). It is important to remember that up to 30% of newborns with meconium ileus have normal IRT levels. The IRT+IRT strategy is applied in only a few autonomous communities.

Figure 1.

Protocols for diagnosis of cystic fibrosis through neonatal screening proposed by the European Best Practice Guidelines for Cystic Fibrosis Neonatal Screening7 applied in Spain.

(0.23MB).

In Spain, there are 3 different strategies currently in use: IRT+IRT, IRT+IRT+DNA and IRT+DNA+IRT.

Genetic testing is part of most protocols for neonatal screening for CF and is performed in samples with IRT levels exceeding the established threshold. In each population, the applied protocol should be adapted to its mutation spectrum.

There are 4 possible outcomes of genetic testing in a newborn with elevated IRT:

• a)

  If the test detects 2 CF-causing mutations, the newborn should undergo a sweat test and DNA segregation analysis should be performed to confirm that each mutation comes from a different parent.

• b)

  In case of a single mutation, a sweat test should be performed. If the results of the sweat test are inconclusive, genetic testing should be expanded to attempt to identify a second mutation. If the sweat test is negative, the newborn is considered a carrier.

• c)

  Cases where no mutation is found and the sweat test is normal are considered false positives of screening.

There is another group comprising those newborns in whom a conclusive diagnosis cannot be made, even with use of ancillary tests, for which the Working Group on CF of the European Cystic Fibrosis Society has proposed the label cystic fibrosis screen positive, inconclusive diagnosis (CFSPID).10 This group includes:

• a)

  Newborns with a CF mutation in only one allele and intermediate sweat chloride values (30–59mmol/L).

• b)

  Newborns with a CFTR mutation in each allele, of which only 1 is classified as causing CF, and normal sweat chloride values (<30mmol/L).

This group of patients requires ongoing follow-up, as in some cases CF is diagnosed at a later age due to onset of symptoms with elevation of sweat chloride levels.

The sweat test is the cornerstone of diagnosis of CF. Newborns with a positive neonatal screen test for CF must be referred for a sweat test exclusively to specialised CF units accredited for diagnosis.

The sweat test is divided in 3 stages: (1) Stimulation by pilocarpine iontophoresis. (2) Collection of a sample over 30min by either of the following methods: Macroduct collection system or the original Gibson and Cooke method (collection in pre-weighed filter paper or gauze). The sample should have a volume of at least 15μL (Macroduct) or weigh at least 75mg (gauze). (3) Chloride determination by coulometric titration with a chloridometer.11

The diagnosis cannot be confirmed based exclusively on the sweat conductivity measurements obtained by the nanoduct or sweat check systems (Macroduct). Samples must be analysed as soon as they are collected.

The test result is classified as “normal” if the chloride concentration is less than 30mmol/L; “intermediate” if it is between 30 and 59mmol/L and “positive” if it is of 60mmol/L or higher.12

Patients with persistent intermediate values should undergo a diagnostic evaluation, including extended DNA testing and repetition of the sweat test at 6 months.

Neonatal screening elicits a varying degree of anxiety in parents. Thus, it is advisable to report the results as soon as possible, preferably on the same day that testing is performed.

If the newborn has CF, parents will be given information on all the tests performed to diagnose the disease and of the encouraging outcomes of new treatments and the extensive research that is underway, thanks to which it is now possible to have an optimistic perspective on the disease.

At the end of the visit, if the newborn is not affected, parents will receive a report stating that the child does not have CF or that the child is a carrier and offering genetic counselling to the parents.13

Follow-up by a paediatric gastroenterologist is recommended, with visits every 1–2 weeks immediately after diagnosis to ensure adequate nutrition and thereon every month for the first 3 months. If the patient is in good condition, subsequent visits may be held at 2- to 3-month intervals.

Treatment for eradication must be initiated as soon as P. aeruginosa is detected for the first time. None of the eradication protocols published to date has proven superior to the others. Based on the Spanish consensus guidelines, the management of a first episode with isolation of P. aeruginosa29 consist in:

(1) Asymptomatic patients: oral ciprofloxacin for 2–4 weeks+nebulised antibiotics—colistin given daily (maximum 3–6 months) or 1–3 on-off cycles of tobramycin or aztreonam (maximum 6 months).

(2) Symptomatic patients: systemic+inhaled antibiotherapy.

- Mild: oral ciprofloxacin for 2–4 weeks.

- Moderate–severe: intravenous ceftazidime+tobramycin (2–3 weeks).

Performance of a respiratory culture is recommended 1 week after completion of treatment. If the culture is negative, we recommend maintenance of daily colistin (for a maximum of 3–6 months) or 1–3 on–off cycles of tobramycin or aztreonam (maximum 6 months).

Treatments are currently available that target the underlying defect that causes the disease. These new therapies aim to improve CFTR function using compounds that act on the protein, which may be correctors (class II) or potentiators (classes III and IV). Ivacaftor (Kalydeco®) is a potentiator that has proven to be efficacious (improvements in lung function and body mass index, and reductions in the chloride concentration in sweat and of the number of exacerbations by up to 52%) and safe in patients with class III mutations.31 The dosage consists of one 150mg tablet every 12h, to be ingested with fatty foods. In Spain, its used is approved starting at age 6 years, and in the United States starting at 12 months.

The combination of a CFTR corrector and a CFTR potentiator, lumacaftor+ivacaftor (Orkambi®), is a new strategy for treatment of patients homozygous for the F508del mutation (class II) that has been shown to improve lung function, the frequency of exacerbations and quality of life.32 The dosage consists of 2 tablets every 12h. It is authorised for use starting at age 2 years in the United States, but is not yet available in Spain.

A chest radiograph is currently recommended in case a complication is suspected or of moderate to severe pulmonary exacerbation.

Chest computed tomography (CT) is the gold standard among imaging tests for the early detection of initial abnormalities (air trapping, bronchiectasis) and their progression, as it is more sensitive than chest radiography.

Bronchiectasis can be found in up to 50% of CF patients by age 5 years.34,35 The CT protocol for assessment of CF should include inspiratory and expiratory views with low-dose radiation. Most hospitals perform a routine CT scan starting at age 2 years (without anaesthesia) and every 2 years thereafter at the time of the annual evaluation, while others do the initial scan at age 4 to 5 years with less frequent follow-up scans.

The lung clearance index is a new and very sensitive test that detects abnormalities earlier than spirometry and can be used to assess ventilation inhomogeneity.36 At present it is used in clinical trials.37,38