Testing for cystic fibrosis (CF) is a part of your state’s Newborn Screening (NBS) panel. For information on newborn screening for cystic fibrosis, read our fact sheet, Newborn Screening Education for Healthcare Providers.
While many newborns may have a positive NBS for CF, it is expected that fewer than 5 percent of newborns will actually have CF. Any infant with a positive (abnormal) CF NBS should be referred to a CF Foundation-accredited care center for further diagnostics.
The time between a positive screen and testing to confirm a CF diagnosis is stressful for parents and families.
Consider informing parents that a positive screen for CF means the newborn may have CF but that most do not. Health care providers need to be aware of this stressful time as they encourage or assist parents to obtain the appropriate follow up tests, without causing undue alarm.
Please refer parents waiting for a diagnostic to the CF Foundation’s website for more information on newborn screening for cystic fibrosis.
How is CF diagnosed?
The early diagnosis of CF through newborn screening depends on an expedited combination of laboratory tests and clinical assessments. These steps, as illustrated in the accompanying figure, are linked together in an essential sequence of diagnostic evaluations. The complete process needs to be accomplished efficiently — ideally before a baby reaches 1 month and certainly by 2 months.
CF is diagnosed if the child has an elevated sweat chloride value or if he or she have inherited two disease-causing mutations in the cystic fibrosis transmembrane regulator (CFTR) gene — the “CF gene.” Infants identified by CF newborn screening are to be referred to a CF Foundation-accredited care center for diagnostic testing by a sweat chloride test. More information may be obtained in the CF care guidelines for diagnosis of CF.
However, sweat chloride values are not always clearly in the diagnostic range and not all CFTR mutations cause CF. Some newborns who screen positive for CF will have intermediate sweat test results and may have CFTR-related metabolic syndrome, or CRMS.
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What is CRMS?
CRMS is also known as cystic fibrosis transmembrane regulator-related metabolic syndrome.
Infants that do not have a diagnostic sweat chloride value (≥ 60 mmol/L) or two CF-causing mutations present the clinician and family with a diagnostic dilemma. In some patients, signs and symptoms may ultimately lead to a diagnosis of CF. Others will develop symptomatic CFTR-related disorders such as pancreatitis or male infertility. Still others will never develop any symptoms.
Infants identified by CF newborn screening programs in whom CF cannot be diagnosed or clearly ruled out are given the designation CFTR-related metabolic syndrome (CRMS; ICD-9 277.9). These patients should be evaluated once a year by a CF specialist at a CF Foundation-accredited care center.
Since families will be making more visits to your office than to the CF specialist, your involvement is crucial. Please contact the CF specialist if an infant with CRMS is not gaining weight, has loose stools and/or flatus, has abdominal pain or has respiratory symptoms such as coughing or wheezing that do not resolve in two weeks. These principles continue to be true throughout the individual’s entire life, as symptoms may not develop until a few years after birth.
Here are the most important things for you to know about CRMS:
- Phenotype is more important than genotype:
- Many infants with CRMS will continue to be healthy and will thrive
- Males with CRMS may be at higher risk of infertility
- Early symptoms can be subtle; open communication with the CF specialist is important if there are concerning symptoms such as:
- Lack of weight gain or unresolved acute weight loss
- Persistent loose stools or excessive flatus
- Abdominal pain
- Coughing or wheezing
- Contact the CF specialist if these symptoms persist for more than two weeks
- If individuals with CRMS develop symptoms they may benefit from current and new treatments.
- The CF care center is a resource for:
- Medical advice
- Psychosocial support for families who have difficulty coping with the uncertainty of this diagnosis
- Information about new developments as they become available
We do not want to create a vulnerable child in the parents’ eyes, since many of these individuals will live a long and healthy life with a low risk of developing signs or symptoms of CF. However, because some will become symptomatic and preventive care is preferable to symptomatic care, we appreciate your special attention to their general health and your support that these children should not be lost to specialist follow-up.
Encourage your parents to read about CRMS.
Please contact the nearest CF Foundation-accredited care center if you have any questions.
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