Determination and characterization of immunoreactive trypsin in amniotic fluid from normal and cystic fibrosis fetuses.

High concentrations of immunoreactive trypsin (IRT) in the blood, and low concentrations of trypsin activity in fecal specimens have been found in newborn infants with cystic fibrosis (CF). The amniotic fluid concentrations of IRT and of IRT in complex with alpha 1-antitrypsin (alpha 1AT) were studied in 39 samples taken in about the 17th gestational week, and in 7 samples taken because the mothers had previously given birth to children with CF. The midtrimester samples contained trypsin in complex with alpha 1AT in a concentration of 30-200 micrograms/liter, and small amounts of trypsinogen, 0-50 micrograms/liter. Three of four amniotic fluid samples from CF fetuses had very low concentrations of trypsin in complex with alpha 1AT (less than 10 micrograms/liter), and only small amounts of trypsinogen (less than 10 micrograms/liter). Further prospective studies are needed to ascertain whether the determination of IRT in amniotic fluid may be of use in prenatal diagnosis of CF.