> Tests on fetal dna in maternal blood NIPT, as it should be used

Not so long ago, I met a patient who had undergone a noninvasive test for prenatal, which was negative for trisomy 21, 18 and 13. The fetus had a few small anormalità ultrasound, but nothing that explains whyé the woman should ask for a diagnostic testing.

At birth the child had a diagnosis of trisomy 18. When I called the doctor, who was not present at the birth, to tell him the diagnosis of the child, he responded, “that’s impossible, the patient had a screening test negative”.

The experience of this patient, unfortunately, not è così as rare as you might think.

These last 10/15 years have been a period of exponential growth of genetic testing in the entire world. Most of these tests are a benefit for patients and for the sanità, in general. A well-known example is the genetic test for mutations in the genes BRCA1 or BRCA2 . Women or men who choose to perform the test for the mutation of the BRCA gene, when recommended appropriately, will have information on their cancer risk that they will increase their skills in decision-making in health care.

The problem that we see with the screening using the NIPT (Non-Invasive Prenatal Testing), however, is linked to the lack of an appropriate counseling, from the laboratory to the doctor, and the doctor to the patient.

Beth Daley show examples of this incorrect perception on the part of patients and providers in a recent article on the Boston Globe, “The prenatal test, super valued, motivates someone to choose abortion”. In this article, Daley gives us examples of cases in which the patients had received news of a prenatal test abnormal but had not received a counseling appropriate about the benefits and the limitations of this test.

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“I Test” sono solo uno screening

In 2007, the American College of Obstetricians and Gynecologists has published guidelines which recommended that all pregnant women, regardless of age, to receive the offer of screening for the Down syndrome. In that moment, the screening test of the first quarter was the più reliable and early for Down syndrome and for trisomy 18 and 13.

This screening was done in the first quarter and combined for the measurement ultrasound of the nuchal fold of the fetus with blood tests, making an assessment of the risk for the three trisomies. The laboratory reports for this screening is usually the “screen positive” or “screen negative”, and it will also provide a numerical data (1 in 50, or 2%) in the printout, which is discussed by the family with the health care provider.

In my experience there was the perception at patients and at health professionals, that a screening test in the first quarter could replace the diagnosis made with the cvs oramniocentesis. To diagnose Down’s syndrome or trisomy 18 or 13, it was necessary to do a chorionic villus sampling or an amniocentesis, secure to 99.9%.

Così as the screening in the first trimester (known as bitest or tritest ed.) the NIPT is a screening, not a diagnostic test. However, because of the way in which è was advertised (using the word “test” in the name, for example), many patients think that this test can replace the chorionic villus sampling or amniocentesis.

When the screening is being advertised as able to give “99% detection for Down syndrome,” even health care professionals make the mistake of thinking that is close enough to 100% to be able to consider the diagnostic.

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The first thing to understand is that the 99% is not applied on the individual result, but, more properly, about the entire population screenata. The test is accurate to 99% for what concerns all women in a screening population.

The high-risk women (those over 35 years, those with previous pregnancy with chromosomal abnormalities, etc) have a higher risk a priori and therefore the predittività a positive test (the ability of a positive test to be a true positività) è più high for these women which have a low risk.

A recent study has shown, through the use of information on the karyotypes in a follow-up on 109 NIPT positive results from different laboratories, in 41 pregnancies with NIPT positive for Down syndrome, only 38 were, in fact, a fetus Down, (93%). The predittività positive was still più low for trisomies 13 and 18.

This type of statistical information are not transparent in the laboratory reports. However, this is the information that patients should understand before you run the test, and, of course, when they receive the results. Patients and caregivers need to understand that there può be a NIPT normal and the same to be a child with Down syndrome. If not c’è a definitive answer but both the one and the other road should be good for the patients, screening può be sufficient, but if not è così the woman should receive information about the options on the diagnostic.

Time and skills required

I do Not know any operator in obstetric and gynecologic or medical doctor who has 30 minutes in his day to discuss all the complexityà screening through NIPT. For many of us, the statistics are not is fun. Without looking above, we remember what it means to predittività positive? If yes, can you explain it to your patients, in correlation with the results of the screening through NIPT?

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The geneticists who perform counseling are certified to do this and to talk about statistics with the patients. Our job is to clearly explain medical information to different populations of patients. As a doctor, if you have access to genetic counselling should use it. Unfortunately, the number of patients who need genetic counseling è much moreù large number of genetic counselors available.

physicians who don’t have easy access to genetic counseling, they can seek it at the National Society of Genetic Counselors. Many clinics and hospitals have a genetic counselor, and può send the patients. Other options include that the laboratories performing these analyses provide the service of genetic counseling. Some of the hospital to the community; provides genetic counseling via telemedicine and some consultant doing it by phone. You could bring in the consultant at your studio one day a week and do the counseling sessions of the group, with a follow up by telephone to the reports.

The screening by NIPT should not be considered to be così as absolute as it seems. Better education and communication between laboratories and health care providers will allowà better care for patients. Leave the genetic counseling to the geneticists bring benefits to your practice and patients.

Fonte: di Margaret B. Menzel – Medscape


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February 12, 2015