Newborn screening and diagnosis of cystic fibrosis

All children born in Australia are screened for cystic fibrosis (CF) via the Newborn Screening Program, which involves measurement of immunoreactive trypsinogen (IRT) from a heel-prick blood sample taken on day 3 or 4 (or usually within 2 weeks) of life. If the blood sample trypsinogen level is above the 99th percentile, it is analysed for the most common CF gene mutations. Results are generally available when infants are approximately 6 to 8 weeks old. An infant with two CF gene mutations is referred directly to a specialist CF centre for confirmation of diagnosis with a sweat chloride test. An infant with only one gene mutation may have CF or may only be a carrier; a sweat chloride test is required.

The Newborn Screening Program may miss up to 5% of children affected with CF per year. Consider referral for a sweat chloride test in any child presenting with a chronic productive (wet or moist) cough, particularly if there is associated failure to thrive or frequent loose, oily bowel motions.

Occasionally, mild CF is not diagnosed until adulthood, either because the diagnosis was missed during screening, or because screening was not done at birth (the Newborn Screening Program was not introduced until around 1990 in some hospitals). Some people with atypical variants of CF have mild disease that does not become clinically significant until adulthood.