|
|
 |
 |
 |
|
|
|||
|
||||
|
||||
Re: Calculation of Risk for DownFrom: Richard M. Roberts (gene@vol.com)Sun Feb 25 14:00:47 2001
Here is my view on this subject. The biochemical markers are screening tests, not diagnostic tests, and the way they are reported in the US is atrocious and statistically fallacious. Genetic counseling is also corrupted by the way these results are reported, and I have been just as guilty as everyone else in utilizing statistically invalid results to inappropriately scare the pants off or falsely reassure the patient based on the foolish reportage of the laboratory providing the biochemical risk. It is high time for us all to realize that the the emperor of biochemical screening has no clothes. Lets analyze this case: Biochemical results --a 35 year old...triple screen risk 1:7600, noted by Joseph A Worrall, MD RDMS. Does the 1:7600 have any real meaning, i.e. her risk is actually 1:7600? NO. What is the real meaning of this figure (which is the same as saying, what should be disclosed to the patient)? First of all, the lab may not make it clear that this is a mid-gestational risk, not the risk AT DELIVERY. They should (but don't) provide both. Would anyone care to claim that providing a risk at midgeststion and not comparing it to the risk at end of gestation (about 1/4 less) would be regarded as inappropriate by any sentient pregnant woman? This is a 35-year old woman. Women 34 or older with negative biochemical screens are at reduced risk, BUT the patient should be informed that 10% to 15% of all infants with Down syndrome will be detectd AT BIRTH, because the sreening test is not a diagnostic test, and has a high rate of falsely negative results. That is the position of the American College of Medical Genetics. http://www.faseb.org/genetics/acmg/pol-15.htm I don't agree with the blanket statement of the ACMG that 2nd trimester biochemical screening should not be offered to women older than 34, but I most definitely believe that any woman that age MUST have full disclosre of the inaccuracy of the testing, so that she may make an informed decision. In order for her to make that decision, she must have a complete explanation of the natural history of an individual affected with Down syndrome (1/3 develop Alzheimers), and she should be informed that if she declines amniocentesis, she is going from a 100% detection rate to an 85-90% detection rate. If she divorces, I have yet to hear of a man who has sued for custody of a severely handicapped child. Who should make the informed decision with regard to whether or not to have an amnio? THE PATIENT. Does 1:7600 have any other real accuracy other than placing her risk under that of a 35-year old? NO. There are no published data to say otherwise. I know of no other test in clinical medicine which is presented as fact, without confidence limits, and thus providing an inappropriate sense of reality as to resuts, than biochemical risk evaluation in pregnancy. "Your risk is 1 in 7600", no more, no less, it is not 1 in 7599 or one in 7601. Very reassuring. BUT there is no difference between a biochemical risk calculation of 1:7600 or 1:279 at midgestation in their real significance. They both have only one known proven result: if a 35-year old woman does not have an amniocentesis, then she will go from 100% detection rate to 85-90% detection rate. We should not be counseling women with such patently imprecise an inaccurate risk figures. As Philippe Coquel states, "it is important to know the confidence limits of the triple screening". Well, we do not, and therefore we should use them appropriately. We should just state whether the woman is at "increased risk" (if higher than the usual risk of a 34-year old), or "decreased risk" if lower. Why have we been kidding ourselves all these years? Now, and ultrasound finding is different. If you repeat a triple screen, you will obtain a result completely unrelated to the first. As a screening test, the next try will tend to regress to the norm. An ultrasound finding, however, if real, is an objective finding which will be able to be seen by any skilled ultrasonographer. If you look again in a day, it will still be there (whereas the next day's triple screen could be normal). So yes, a reasonable analysis predicts that ultrasonographic findings are independent of statistical biochemical screening. Why on earth should any of the unusual physical features in Down syndrome have any influence on biochemical screening? How would a flat midface, incomplete outfolding of the scapha helix, prominent ears, inwardly-curing 5th interphalanges, redundant skin over the back of the neck, relatively short femora and humeri, even duodenal atresia, have any bearing on the levels of biochemical markers? You are comparing physical findings to abnormal cellular biochemistry. Can't be done. I happen to like Nikolaides' division into "hard" and "soft" ultrasonographic findings, based on outcome of, I believe, over 100.000 successive first and second trimester ultrasounds. He classifies echogenic bowel as a "hard" sign--which means offering aminocentesis after explaining the increased risk to an 18-year old, let alone a 35 year old. AND DONT REPORT AN INCREASED RISK AS ABNORMAL. IT IS NOT ABNORMAL, IT IS INCREASED RISK. Please pardon my capitalization. Regards, Richard (gene)
>>There is reasonable evidence to indicate that ultrasound and
-- Richard M. Roberts, PhD, MD, FACMG
|
|
Return to
|
Mail a New Message to the Forum: ultrasound@obgyn.net Forum Administrator: terry.dubose@obgyn.net Report Technical Problems: webmaster@obgyn.net Last Updated: Thu Oct 2 05:18:03 2008 |
The American Medical Association is no longer designating CME hours for AMA Category II CME credit. However, physicians themselves may self designate learning activities as Category II CME credit hours if they feel it is of sufficient educational merit and meets the formal definitions of continuing medical education. OBGYN.net believes these interaction in this forum meets these criteria. For further information see the AMA web site.