Saliva Samples vs. Blood Samples

Hi! My name is Gwen Connor. I’m a genetic counselor with Insight Medical Genetics. Today I wanted to talk about one of the questions that I get a lot lately, which is about using saliva samples instead of blood samples for genetic testing. People ask, “Are the results you get from a saliva sample as accurate as from a blood sample?” The short answer is, “Absolutely, yes!” But I was always taught that if we know the reasons why something is the way it is, the answer will always make more sense. And the reasons why in this case are also super interesting, so I wanted to talk it through for you here. In talking to people about genetic testing, most of us seem to understand that the way it works on TV is not the way it works in real life. And it makes sense to a lot of us that in order to get accurate, specific, meaningful genetic test results, a blood sample would be needed. We are used to having blood drawn for a variety of medical reasons and we all know that our blood carries a lot of information that tells our doctors about our health. And indeed, historically, extracting DNA from blood has been the gold standard for most genetic testing. It has always been true, however, that not every person who needs a genetic test can give a blood sample. There are a lot of reasons for this – sometimes there is a medical reason, sometimes it’s a very strong fear of needles, and sometimes, its lack of access to a person who knows how to draw blood. Thankfully, scientists and researchers have determined that there is an easier way to get a sample of DNA from patients through saliva! As you may remember from biology class, almost every cell in your body contains a complete set of the DNA that you inherited from your parents. In blood samples, the DNA is extracted from white blood cells, or leukocytes, because there are a lot of these types of blood cells in your blood stream at all times. In fact, there are between 7,000 and 25,000 white blood cells in a single DROP of blood. In a small tube of blood, therefore, we can get millions of white blood cells, each of which contains a complete set of your DNA. It is then easy to extract enough high-quality DNA from such a sample in order to perform highly-accurate, medical genetic testing. It turns out that the cells we find in a saliva sample are both epithelial cells (or cheek cells) and white blood cells. And there are more than enough white blood cells in the typical saliva sample to extract the necessary amount of DNA for highly-accurate, medical genetic testing. In both blood and saliva samples, we are able to get the same type of cells, therefore we are testing the same thing – just getting it from two different parts of the body. Therefore, results from genetic testing from saliva are just as accurate as results from genetic testing from a blood sample. There are a few draw-backs to using saliva instead of blood, but they have nothing to do with the accuracy of the results. In order to make sure that there are enough white blood cells in the saliva to do the genetic testing, you need to have nothing to eat or drink, and you can’t smoke or chew gum, for at least 30 minutes prior to providing a saliva sample. If you drink anything, even water, it can dilute the sample and you’ll have more water and less white blood cells in your sample. If you eat anything, the DNA from what you are eating can contaminate your sample. The machines that help scientists analyze DNA are very touchy and they don’t like it when they detect chicken or lettuce DNA in a human sample. So the main “risk” of using saliva instead of blood for genetic testing is that, if the sample is not collected correctly, the sample will fail and the lab won’t be able to provide the requested information. However, if there is enough uncontaminated DNA in a saliva sample, it is just as accurate as from a blood sample. In these times of social distancing, when we are all doing our best to minimize contact with other people as much as possible, Virtual Insights, our tele-genetic counseling service, can provide genetic counseling by phone or secure video consultation. If genetic testing is needed, in many cases, we can then send a saliva kit directly to your home. You collect the sample at your convenience and simply place the kit in a mail or drop box to send it back, with no contact needed. And now you know that you can rest assured that the results you get from your saliva sample are just as accurate as they would have been from a blood sample. So if you’ve been meaning to make that appointment with a genetic counselor, no need to delay! We can help you check this important item off of your list now.Thank you for watching. I hope you found this video to be informative. If you’d like more information or if you’d like to make an in-person or a tele-genetic counseling appointment, call at 888-864-9756 or visit https://www.insightmedicalgenetics.com/ I wish you the best of health