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Re: Calculation of Risk for Down From: Ph Coquel (philippe.coquel@wanadoo.fr) Fri Feb 23 05:36:51 2001 Messages sorted by: [ date ][ thread ][ subject ][ author ] Next message: zalel: "=?windows-1255?B?4fLw6envOiBDYWxjdWxhdGlvbiBvZiBSaXNrIGZvciBEb3du?" Previous message: Morag Campbell: "3D Multiplanar Endometrium" Maybe in reply to: Allen Worrall: "Calculation of Risk for Down" Next in thread: Doc Gyn=?ISO-8859-1?B?6Q==?=co: "Re: Calculation of Risk for Down" Yours arguments are correct It is necessary to apply the risk of hyperechogenic bowel the triple screen risk(1:7600) : It is an application of Bayes's theorem In theory, you must apply LLR to odds and not to risk, but in fact and in practice in our range of prevalence, it is about the same thing An important point is the confidence limit For example, if you use data from De Vore in UOG , for non cardio vascular ultrasound markers with a sensitivity of 60% and a false positive rate of 5.9%, the estimed likelihood ratio is 7.24 but is situated between 3.71 and 14.84 with an error of 5% (95% CL). The upper level is about twice the estimated LR LLR: 5.5 risk =1/1382 LLR:7.24 risk =1/1050 LLR: 14.84 risk= 1/512 (upper risk with De Vore data) It is necessary to calculate the risk with the upper LLR , particularly in border line examination For this reason, it is important to know the confidence limits of the triple screening In your case, the problem is the absence of examination of the nuchal translucency during the first trimester with a borderline nuchal fold during the second trimester, two major signs in aneuploidy 35 year old, without examination during the first trimester, a borderline nuchal fold , hyperechoic bowel: I think that an amniocentesis is indicated -- Ph Coquel,MD Annecy, FRANCE >----- Original Message ----- From: "Allen Worrall" <jworrall@alaska.net> To: "Multiple recipients of list ULTRASOUND" <ultrasound@mail.medispecialty.com> Sent: Friday, February 23, 2001 7:11 AM Subject: Calculation of Risk for Down > I am aware that a negative ultrasound can reduce the risk assigned by a > triple screen, by about 50%. > > What about a patient who has a very low risk Down Triple screen result, > but one soft marker is found? Can the soft marker likelihood ratio be > applied to alter the triple screen risk? > > Case in point: 35 year old with 4 previous C Sections, triple screen > risk 1:7600. I found hyperechoic bowel (it seemed to me it was as > echogenic as bone, but I find this a little subjective), 19weeks > gestation, nuchal fold 5.4 mm, and a scan was not requested at 11-14 > weeks. On today's scan I found no other anomalies or "soft" markers. (I > think Dr. Nyberg would consider a nuchal fold of 5 mm or greater as > significant, Dr. Benacerraf 6 mm or greater). > > If we say the nuchal fold was normal (not yet 6 mm or greater): > hyperechoic bowel has a likelihood ratio of 5.5. If we consider her age > related a priori risk, it is ~ 1:302 at twenty weeks. Apply the > likelihood ratio for the hyperechoic bowel and her risk is now ~ 1:56, > clearly an indication for amniocentesis. Also if we use Dr. > Benacerraf's scoring system, age 35 and score 1, amniocentesis should be > recommended. > > Or should the 5.5 likelihood ratio be applied to her triple screen risk > of 1:7600, which would increase her risk to 1:1382,and thus > amniocentesis not indicated? > > I suspect the answer is that the patient should be offered > amniocentesis, but I would like to see what others think about this. > > -- > Joseph A Worrall MD RDMS > Fairbanks, Alaska Next message: zalel: "=?windows-1255?B?4fLw6envOiBDYWxjdWxhdGlvbiBvZiBSaXNrIGZvciBEb3du?" Previous message: Morag Campbell: "3D Multiplanar Endometrium" Maybe in reply to: Allen Worrall: "Calculation of Risk for Down" Next in thread: Doc Gyn=?ISO-8859-1?B?6Q==?=co: "Re: Calculation of Risk for Down"

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