When I first began practice, we needed to wait until a baby was at least 72
hours old to obtain a blood sample for a reliable test for PKU (the main
condition screened for in newborns). After some years, the analysis
technique was improved and the tests were sufficiently reliable at 60 hours
after birth.  A couple of years ago they made changes again, and now we are
asked to obtain the blood sample as close to 48 hours after birth as
possible.
In the case of PKU they are looking for substances that begin to accumulate
in the baby's blood as soon as the baby is on its own - without regard to
how much or how little protein the baby has ingested.

I see the expressions 'false negatives' and 'false positives' have been
used in several posts. A false negative result is when an individual who in
fact has a given condition, tests negative for the condition. A false
positive is when an individual who in fact does NOT have the condition,
tests positive for it.  When reading the posts in this thread, it seemed to
me that these ideas were reversed.

A very sensitive test will give a lot of false positive resutls (a good
example is the doorstep fetal monitor strip - a lot of them look alarming
but almost none of the babies are actually in any danger). A
not-so-sensitive test will give a lot of false negative results, i.e.
individuals who have the condition being tested for, may not be
discovered.  When choosing screening tests, one of the things considered is
how many false positives it will generate, requiring follow-up testing of
heatlhy people to determine whether they are in fact at risk for anything,
and how many false negatives, i.e. how many people with the condition in
question will be missed by the screening procedure.  Generally we shoot for
a test that is a little more sensitive than necessary, rather than that is
not sensitive enough.

Rachel Myr
Kristiansand, Norway

             ***********************************************

Archives: http://community.lsoft.com/archives/LACTNET.html
To reach list owners: [log in to unmask]
Mail all list management commands to: [log in to unmask]
COMMANDS:
1. To temporarily stop your subscription write in the body of an email: set lactnet nomail
2. To start it again: set lactnet mail
3. To unsubscribe: unsubscribe lactnet
4. To get a comprehensive list of rules and directions: get lactnet welcome