Letter: Screening for cystic fibrosis.

Screening for cystic fibrosis (C.F.) in the newborn has been in vogue 
since the introduction of a rapid simple test based in the 
presence of albumin in the meconium of C.F. babies. False-positive tests 
have been observed in prematurity or when the specimen is contaminated 
with blood. We have reduced the number of false positives by 
additional studies on the meconium, including detection of lactase. Lactase activity 
can be detected in meconium from babies with C.F. but not 
in meconium for healthy babies. In testing 200 normal meconiums with 
a negative albumin test we noted 3 positive tests for lactase. 
These 3 patients did not have C.F. These false-positive lactase tests 
could be distinguished by the addition of distilled water to the 
meconium instead of lactose. This simple test may provide an additional 
or alternative method for detection of C.F. in a screening programme. 
When this test is used in addition to the albumin test 
the number of false-positive albumin tests will be reduced. 