Here is an ariticle I found. It's not very helpful but it does indicate that false positives do occur.
False Positives and a Potential New Model
Presenter: Jeannette E. Dankert-Roelse, M.D., Vrije Universiteit Medical Centre, Amsterdam
Screening for disease can be carried out by means of a standardized test. Screening is meant to identify asymptomatic patients with the aim of preventing outcomes of disease due to the natural course of disease. In the absence of a perfect test, a screening program inevitably will involve false positives. In neonatal screening for CF, false positives elicit anxiety and parental stress, but may also convey knowledge of carrier status. Do false positive tests provoke unnecessary parental anxiety? Other questions are if the early diagnosis of CF causes harm, and if another screening strategy should be chosen? After a false positive test practically all parents appear to worry, but most feel that their child is healthy if they develop well. Ninety-four percent reported feeling relief immediately after normal sweat tests, as well as on the long term, but about 6-10% keeps worrying.
Despite false positive tests, 90-95% of parents thought that CF screening should be added to an existing neonatal screening program
In an exploratory study Baroni et al (Pediatric Nursing 1997;23:143-151) compared parental stress in families with a false positive screening tests to families from a general pediatric clinic. The study showed significantly lower stress scores in the families with a false positive screening test.
All babies with positive IRT/DNA screening tests have at least one CF mutation, so a normal sweat test indicates that the baby is healthy but a CF carrier. All parents should therefore be offered genetic counseling and carrier testing.
The main ethical concern about early knowledge of the childs carrier status is that the newborn's consent cannot be obtained, which violates the individual's freedom of choice "not to know." Most studies of parental attitudes about the knowledge of their child's CF carrier status show that most parents are glad to be aware of it. Most parents are neither confused nor feel guilty, but ~25% feel anxious about their childs CF carrier status. After genetic counseling, 90% of couples accept testing of one or both parents and 85% of parents of a child carrying one CF-mutation think that newborn screening should be done.
Mérelle et al (Pediatrics 2003;111:346-50) explored the following questions 1) does the early knowledge that the baby has CF cause harm?; and 2) do parents of children with an early diagnosis of CF experience the disease of their child in a manner other than parents of patients with a late diagnosis? Most parents experienced the pre-diagnostic period negatively, but significantly less in the early diagnosis group than in the group with a late diagnosis(61.9% versus 85.2%, p<0.05). There was more confidence in the medical profession by the early diagnostic group, and 98% of all parents favored neonatal screening for CF.
In summary, the research shows that false positive tests without revealing CF carrier status cause only short term worry. And, while knowledge of carrier status increased anxiety among parents identified as CF carriers, there has been no evidence found that early diagnosis of CF is associated with psychosocial harm. The attitude toward neonatal screening by more than 90% of parents was that neonatal screening for CF should be offered.
Alternative approach. Since identification of carriers is not the goal of newborn screening, the number of false positive tests in newborn screening for CF should be as low as possible.. The present DNA technology could allow for another line of approach in screening, and this may lead to a specificity of nearly 100%. This approach begins with the IRT test. If it is below the cutoff level, the risk of CF is negligible. But if it is above, the oligonucleotide ligation assay (OLA), which focuses on 31 CF locations, is done. If a normal gene analysis results, again, the risk of CF is negligible. However, if one mutation is found, a denaturing gradient gel analysis (DGGE) is done. If the result stands, again the risk of CF is considered negligible. If two CF mutations are found, either by OLA alone or by OLA plus DGGE, this practically assures diagnosis, but a sweat test should be done to confirm that. All test results with a negligible risk for CF are considered screen negative, and the parents will not be informed.
Using this process, false positive tests should occur very rarely, and the diagnostic sensitivity would be raised.
Discussion included:
Dr. Dankert-Roelse's suggested framework was well received by some as potentially able to identify ?90% of cases and to reduce false positives. The testing would cost more, but that would decline with expanded use, and the screening would identify carriers. But if a child is found with elevated IRTs, would the test then not be indicated? It also could be regarded as a serious problem to have carrier information and not pass it along.
Dr. Audrey Tluczek reported that the University of Wisconsin is now doing a new cohort study of the psychosocial issues. They have had findings similar to Dankert's; while waiting for sweat test results, the parents are clinically depressed, which is drastically reduced with the sweat test results. Dr. Dankert added that the false positive rates for CF do not differ from those of any other tests. The parents with a false positive test for congenital hypothyroidism showed the same results. What parents remember of these periods is relief that the child does not have the disease they worried about.
Can't imagine how frantic they must be over this.
