Testing newborns for cystic fibrosis.

Testing newborns for cystic fibrosis 

Babies born with cystic fibrosis can go months or years without showing the lung damage or mainutrition that eventually disables them and kills half of them by age 28. Even when infants show early symptoms, they may go through several hospitalizations before the traditional "sweat test" pinpoints the disease.

The sweat test, although highly accurate, takes one or two hours per patient and requires specialized equipment and training. These limitations confine its usefulness to diagnosing children who already appear ill.

Researchers have now demonstrated the reliabilty of a simple, inexpensive method for routinely screening newborns for cystic fibrosis, reports Frank J. Accurso of the University of Colorado School of Medicine in Denver. The study by Accurso and his colleagues, which involved testing nearly every baby born in Colorado over a five-year period, also revealed that treatable abnormalities can occur before obvious symptoms of the disease appear.

Costing about $2 per child, the test measures the amount of immunoreactive trypsinogen (IRT) in a spot of dried blood. Normally, the body processes trypsinogen -- secreted by the pancreas -- into the digestive enzyme trypsin; in children with cystic fibrosis, some trypsinogen instead enters the blood-stream.

In the study, 1- or 2-day-old babies who showed elevated IRT concentrations were tested again when they were 3 weeks old. About 900 of the nearly 280,000 babies received the second IRT test, which indicated that 78 had the disease. The researchers confirmed the diagnoses with the sweat test. The final rate of 1 cystic fibrosis case per 2,400 Caucasian babies tallied well with the U.S. incidence of the disease. Only five cases slipped through the screen -- about the same failure rate as standard neonatal tests for other genetic diseases such as phenylketonuria and sickle cell anemia, Accurso says.

Before hospitals adopt any early, routine screen for cystic fibrosis, he says, researchers must address three questions established in 1983 by a special task force: Does the test adequately identify the disease? Does early detection help the infant? Does telling parents that their seemingly healthy baby has a fatal illness cause psychological problems?

IRT's low failure rate makes it an effective screening tool, Accurso contends. In addition, spotting the problem early revealed that afflicted newborns suffer previously unrecognized abnormalities in growth, nutrition and digestion, and can benefit from early treatment such as supplemental digestive enzymes, he says. Early detection also uncovered a relationship between low levels of the protein albumin in the blood and later lung damage.

The researchers interviewed a small group of parents whose children had cystic fibrosis, diagnosed either in infancy with the IRT screen or later through the conventional diagnostic process. All of these parents said that discovering their child had cystic fibrosis proved psychologically traumatic, but they unanimously preferred early diagnosis to avoid the waiting game of conventional diagnosis and to give the baby a chance for early treatment, Accurso says.

Last month, researchers reported they had identified the gene responsible for cystic fibrosis (SN: 9/2/89, p.149) -- a feat that may lead to sophisticated genetic techniques for screening babies and fetuses and for identifying the estimated 1 in 23 adult in the United States who carry the defective gene. Although genetic testing may eventually supplant IRT screening and sweat tests, the Colorado study offers hope for widespread neonatal screening in the near future and high-lights the physical and psychological importance of early diagnosis and treatment, Accurso says.