Guthrie test in pancreatic sufficient people

Question

Hello,
will pancreatic sufficient babies be detected with the Guthrie test if they have cystic fibrosis?
Cordially

Answer

Hello,

The Guthrie test actually refers to the test used for the first systematic neonatal screening of a genetic disease: phenylketonuria. In every day language the wording Guthrie test became used for screening tests of other genetic diseases which are done on the same sample of blood from the heel of the newborn and it is absorbed onto filter paper: phenylketonuria, cystic fibrosis, congenital adrenal hyperplasia, congenital hypothyroidism, sickle cell anemia... If screening for these diseases is made from the same blood sample, tests used are specific for each disease.

Routine newborn screening test for cystic fibrosis IRT-DNA combines, particularly in France, the blood concentration of a pancreatic protein (immuno recative Trypsin - IRT) and the search for mutations of the cystic fibrosis gene with a kit using the 30 most frequent mutations. This test identifies the vast majority of newborns with cystic fibrosis but is negative in about 5% of them: they are called screening "false negative" and will be identified and diagnosed on suggestive symptoms in the following months or years.

The last false negative survey of newborn screening for cystic fibrosis led by the French Association of Testing and Prevention of Child’s Handicaps (AFDPHE) found exactly the same proportion of false negatives (48%) in pancreatic sufficient children and pancreatic insufficient children, information on pancreatic state being missing for the remaining 4%.
The proportions of false negatives are identical in the 2 groups, however, pancreatic sufficiency is about 5 times less common than pancreatic insufficiency in infants with cystic fibrosis, so it can be concluded that the IRT-DNA testing is less sensitive in case of pancreatic sufficiency.

Hope this answer can help.
Best wishes
Gilles RAULT, MD, Roscoff CF Center

18.04.2016