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Screening vs. Diagnostic Testing (Nursing)

by Jacquelyn McMillian-Bohler

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    00:00 Some other tests that we may do kind of fall in the category of screening and diagnostic.

    00:06 So it's really important that we know the difference. So I want to spend a second talking to you about that. When we do any test to screen what that means is there's a possibility that the client could be experiencing whatever it is that we're looking for. It's not 100% and you can always look at the percentages to determine how actually correct it might be versus something that's diagnostic. If it's diagnostic, we know that if it comes back positive, then it means the patient has that particular disorder that we're looking for. So screening means there is a chance, diagnostic means it's definitive. So keep that in mind as we go through the next few tests. When we think about talking to a client about screening, we need to have certain information in order to be able to interpret the results. We want to know the client's age because specifically in this case we're usually looking for risks for genetic abnormalities and the older a client is, the more at risk they might be. So we need to know their age, we need to know their history and their family history in order to make a recommendation. We need to understand what their access to care is. So we don't want to order screening test if we don't have the tools in order to take care of the results if it comes back not good. Right? But don't want to subject the client to finding out that their baby may have a disorder that we have no way to treat. Also looking at gestational age, because many of the screening tests that we do are based on hormonal levels which change as we progress through pregnancy. So we want to make sure that we have an accurate gestational age because that's going to be factored in. We want to know the number of babies that are inside because the more babies you have, the more hormone that may be released and that could actually affect the results of some of our screening tests. So if we think we have 1 baby and they're actually 3, then a test could come back positive saying that we have a genetic abnormality and it may be just because we have more than 1 baby. And then we also have to talk to the client and their support person about what are the desired outcomes for the pregnancy. So, are they having the test for curiosity or they're having the test and they're not sure what they would do if the results come back positive because once you get those results, then there tends to need to be a response. So maybe they don't want to screen because it's not going to change what they're going to do and that's a perfectly great reason to refuse.

    02:28 Okay. So let's look at some of the tests. So, the ultrasound is going to be perhaps the one we know the most about, the one we see. So here is a graphic of a wonderful sweet little one and we can do what's called an anatomic screen, so remember screening means it's not diagnostic, it lets us know there may be some issues. We typically do this screen around 18–20 weeks or so. That's when we know the organs are large enough especially the heart that we can see the 4 chambers and we can look at the heart and the lungs and the kidneys and the arms and legs and toes, and we can make a good estimation about what the fetus looks like. Okay. Is there a sign that there is an obvious genetic abnormality? We can do an ultrasound a little bit earlier at the end of the first trimester, beginning of the second trimester to look for what we call nuchal translucency. And there is actually some fluid that naturally builds up sort of on the back of the neck of the fetus. If there is too much fluid, then that's an indication that there may be a genetic abnormality. So, not to be confused with nuchal folds, those are different. This actually looks at the fluid behind the baby's neck. We can also do screening tests that are blood tests and there are several different types. It's not important always that you're able to identify the types because it's going to differ by the company that's doing it, but generally thinking about when we do the screening will help you keep all these together. So, generally speaking, first trimester screening is about 80% accurate in picking up genetic abnormalities. Remember, we're using the word screening so it's not diagnostic, so there is a chance that the information we receive from this test could be positive and not be right or negative and not be right. A quad screen is done around 16 weeks or so and it has about a 90% accuracy. So definitely a little more accurate than a first trimester screening, but a noninvasive prenatal screen and NIPT is what it's usually called, has about a 99.8% accuracy rate. So it's actually pretty good, it's still not diagnostic but it is very accurate in terms of letting us know there may be a genetic abnormality. So remember, diagnostic testing is 100% accurate. We're going to actually line up that whole chromosomal chart, so all 23 pairs of chromosomes will be there so if there is a trisomy or a missing chromosome or even in determining the sex we can see that definitively 100%. There are 2 diagnostic testing options that we're going to talk about. One is called the chorionic villus sampling and the other is the amniocentesis. So let's first talk about the chorionic villus sampling. Now when we take a chorionic villus sample, we need an ultrasound. There is a needle involved and we absolutely want to make sure that we're in the right place. So under ultrasound guidance, we will approach this in one of two ways. One, through the abdomen using a needle we'll go through the abdomen, through the uterus, and in to the placenta to capture a small piece of the chorionic villi. We can also use a catheter and go through the cervix and into the placenta in order to capture those same cells. So this is what a chorionic villus sampling test looks like and this is how we capture it. So how do we prepare the client for CVS testing? Well, this procedure can result in loss of the pregnancy so we want to make sure that the provider has talked to the client about that. We want to make sure the client has signed a consent really indicating that they're aware of the risks and they feel comfortable with that. We want to make sure the bladder is empty so that it doesn't get in the way of the needle and the if the patient is RH negative then we want to make sure that we give Rhogam.

    06:09 I promised I would talk about this blood incompatibility thing and I will, so just hang on.

    06:15 When is this test done? It's done around 10–14 weeks and the exact timing of that is going to depend on the person who does the test. So that's going to be individualized depending on the provider. And then the results are going to detect chromosomal or genetic abnormalities.

    06:31 Remember the chart. Let's look at the amniocentesis. Again, this is done under ultrasound guidance and this time we're still using a needle, but we're not getting chorionic villi, we're actually getting fluid. So think about amniotic fluid, amniocentesis, we're actually capturing the fluid because within that fluid they actually feel cells floating around and we can get chromosomal information from those cells. So we will insert a needle through the abdomen into the amniotic fluid, extract some of that fluid and then we can send that off to grow cells and actually be able to collect that genetic information. So what do we do? We still need to prepare the client because yes there is a risk for infection, there is a risk for loss, and the patient needs to understand that. We want an empty bladder again because we're going to put a needle into the abdomen and we don't want the bladder to cause any problems or be in the way, we're going to give Rhogam if the patient is Rh negative. Timing for this is usually going to be after 15 weeks. Why? Well, because we have to have enough amniotic fluid in order to get some out. So after 15 weeks in general, there's going to be sufficient enough amniotic fluid that we can do that. And then the results are going to be very much the same as a chorionic villus testing in that we're going to have the chromosomal chart. Why would a client choose to have a CVS or chorionic villi sampling over an amniocentesis? Remember the timing. So, thinking about having a CVS at 10 weeks is very different than an amniocentesis at 15 weeks. It takes much more skill to do a CVS and so the risk of having complications or loss is going to be much greater. So, when clients need to have that information early and they've got a provider that is very skilled, a CVS is a perfectly wonderful option and the amniocentesis can be done a little bit later and it's also a little bit easier to do.


    About the Lecture

    The lecture Screening vs. Diagnostic Testing (Nursing) by Jacquelyn McMillian-Bohler is from the course Antepartum Care (Nursing).


    Included Quiz Questions

    1. The client's age
    2. The client's access to healthcare
    3. The client's desired outcome for testing
    4. The client's allergies to medications
    5. The client's annual income
    1. Indication of the baby having anatomical and genetic abnormalities
    2. Diagnosis of the baby having spina bifida
    3. Possibility of the baby having Down Syndrome
    4. Confirmation of whether or not the baby will be vaginally delivered
    1. The amniocentesis has fewer risks of complications or loss
    2. The amniocentesis is less painful for the mother
    3. The chorionic villi test has fewer risks of complications or loss
    4. The chorionic villi test is less painful for the mother
    1. The client must be administered RhoGAM if they are Rh-negative
    2. The client must sign a consent form prior to the exam
    3. The results will diagnose chromosomal or genetic abnormalities
    4. The tests should both be done between 20 and 24 weeks.
    5. The client's bladder must be full prior to the test

    Author of lecture Screening vs. Diagnostic Testing (Nursing)

     Jacquelyn McMillian-Bohler

    Jacquelyn McMillian-Bohler


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