Challenges of Saliva Testing

- This is lab medicine rounds, a curated podcast for physicians, laboratory professionals and students. I'm your host, Justin Kreuter, the bow tie, bandit of blood a transfusion medicine pathologist at Mayo clinic. And today we're rounding with Dr. Darci Block, an assistant professor of laboratory medicine, pathology, and consultant in clinical core laboratory services here at Mayo clinic to talk about the challenges of saliva testing. So thanks for joining us today Dr. Block.

- Yeah. Thank you, Dr. Kreuter for having me, I'm excited to be featured on this podcast, 'cause I haven't been yet. - Well, Hey, we came across an article of you talking about or where you were interviewed talking about saliva testing and we said, how can we fast this up? So I'm kind of curious why is

the medical field interested in saliva? - So I can only really speculate. I'm actually not an expert of saliva testing at all but I think that the interest really grew maybe exploded during the COVID pandemic when there was a major lockdown but yet this desire to be able to test, either as a population or, so you can see if it's safe to go visit your grandma to be able to have access to testing for COVID during the pandemic and now moving forward.

And I think it just represented an easier way so that we could avoid so many nasopharyngeal swabs and other more, those invasive type tests that require, a medical person to collect. - Yeah, I feel you on that. My youngest daughter is really quite nasal swab adverse, as probably most of us. So that ease of testing that really kind of is a theme that we see in laboratory

medicine or at least it seems like it. What sorts of information could be gleaned from saliva? - Yeah. So I think, I think the medical community thought of saliva because it's not a new matrix for testing. So we know that it's useful or can be used in a variety of different settings. So salivary cortisol is kind of that primary example we think of in chemistry, as because it's a sample that needs to be collected at a particular time of the day.

That's not really amenable to being at the laboratory, it's kind of a midnight collection. So if you can tell a patient to, set your alarm and spit in a tube and send it to us, and we get the answer we need, it makes it more convenient. So I think the convenience aspect has been around, also featured in that article, you referenced where some other researchers who, are looking at being able to try and screen populations for things like, upper GI face, head, neck, cancers.

And so, again, trying to do a lot of testing at a population level, they're looking at saliva is, really helping to accomplish that. - I hadn't thought about that.

I mean, I get you on the ease of use but I had forgotten about kind of the timing and how that also kind of plays into getting the sample, when you need it. I'm kinda curious. I mean, just on the, at the 10,000 foot view, are there certain limitations of what could come out of saliva testing?

- Yeah. So it's not going to be perfect for any test and probably very few tests in actuality really because, saliva is kind of... to really over oversimplify the composition of it it represents sort of an ultra filtrate, of what might be circulating in blood.

So for example, the cortisol will show up there but the sensitivity of our methods are such that we're, they're designed to measure analyte concentrations that you would see in blood but they may be at much lower concentrations in saliva and therefore be undetectable. So that's a problem. The reason I think they reached out to me to talk about this topic was when it comes to testing saliva on as an alternate specimen type, we have to think about things like matrix interferences.

Actually one of the biggest challenges is actually in the collection itself. So, if you just give someone a tube and say, "Spit", there's a lot of different things that come into play, what did they use to clean their teeth with that morning? Could that interfere with the testing? Some of the tests have a larger volume requirement. So to say, and so, there's some protocols

where you actually give them like a little sucker that has, citric acid or something kind of sour to induce saliva flow. And so then you have to think about, well does the different components or foams, or different things that we use that could potentially interfere with testing. So it's very nuanced, I would say. - Oh, interesting. Yeah, so we've got students that are listeners of this podcasts. I wonder if you could just kind of elaborate what you mean when you say matrix.

- So really that composition of the sample if you think about blood, it has a lot of protein, a lot of different types of factors, coagulation factors, small analytes, big analytes at a whole spectrum of concentrations. And so when we even just pipette a sample there's a viscosity difference between, something like water or serum, versus even just whole blood or some of the sticky gooey things that come out of other places of the body.

So we have to just keep in mind that the composition of it could potentially interfere or its actual physical properties could make it,

less amenable to being able to go through that testing process, the pipetting et cetera. - And given you were talking about the different possibilities for interference, like the idea of, maybe the type of toothpaste that I might use. I mean, I don't know, interestingly enough as you said that I was thinking, nowadays it seems like the, the charcoal in the toothpaste is something that I see when I go and get toothpaste for myself and my family.

And, and I mean, charcoal has been long known as a substance that can, absorb certain things out of our, it can absorb certain things. And so I'm curious, how does one... as somebody who runs saliva testing in their lab how do you approach navigating what could be interferences? 'Cause as you're saying, right, we always wanna be giving accurate test results to our clinicians or as accurate as, catching these things that may be interfering with the ultimate result.

- Yeah. So we, this is not unique to my laboratory. All of our laboratories have to demonstrate accuracy precision, et cetera, for the tests, even tests that are meant to be used for that sample type. So for the example of blood or a urine sample we have to verify that the test actually performs correctly. So when we change the specimen type, such as testing saliva, we have to verify.

And usually we do that by, some accuracy studies things like spiking in a known amount of the analyte and being able to demonstrate that we recover that concentration back out that there isn't something that's, either sponging it up or causing a falsely elevated signal, for example. So those are the types of things that we wanna do. The other really important thing for variables such as that is when these tests

go through the development process they would typically have a... you might test, a number of these variables and then verify, it matters or it doesn't matter. And then you kind of have to set a fairly strict protocol for, using this container, this device, et cetera, et cetera, this time of the day, all of those things kind of get into that protocol. And then when you move forward it minimizes that variability when it comes to, the actual results.

- Yeah. I'm gonna get myself in trouble here when I ask this. But would that be considered part of the matrix, or the matrix is just the specimen itself? Not exactly all the, like you said, collection parameters around it. - So yeah, when we think of matrix we think the specimen itself, but from the total test process, we don't wanna be blind to it.

I actually just attended a pre-analytic meeting that the American Association for Clinical Chemists puts on last week and it's dedicated to that entire, especially pre-analytic being from time of order to

at least by the time the sample gets collected or really tested on the instrument. There's a lot of things that goes into that. And it's one of the primary areas that contributes to testing errors as we think of them in medicine about 70% of errors occur in that pre-analytic time period. So I don't like to isolate the matrix sample alone. It's important to, expand the scope and and not be blinded to those other impacts.

- I'm so glad you mentioned that stat 70% of errors happening in that pre-analytical phase. So that makes me think another population that is our audience is clinicians. And so I'm kind of curious, could you kind of elaborate maybe unpack those pre-analytic variables that like a clinician may have kind of top of mind or what might be in their kind of sphere of control, influence, awareness.

- Yeah. So things that we think of in that phase that a clinician could directly possibly impact are ordering the right test. So sometimes we call tests confusing names and so we wanna make sure that we're actually ordering the right test and it's not confusing. And then when, a lot of the errors that we see in the laboratory are related to labeling.

So actually making, verifying the patient's identification printing a label at bedside and only that label and a fixing it to the sample and, making kind of closing the loop and making sure that there's no other, pre-printed labels that could be in the environment that could accidentally be placed on it, et cetera. And then from there it's transporting the sample to where it gets tested, under the conditions that are specified. So again, that goes back to how stable is the sample.

Can it be exposed to light air? All of those things that you have to work out when we validate these tests. And so making sure there's a system in place so that you know how to do what you need to do is important.

And then really from there, the laboratory kind of takes over and there's routing and pre-processing and other things can, that could go wrong, that we try to mitigate. - That's awesome and I think not only does that give people kind of some thoughts to reflect on, but also, I mean, it really resonates with my experience before I got into pathology as a medical student. I had no idea of this kind of, this nuances complexity of what things were named.

I think that's largely 'cause my world as a young medical student was a lot more simple. It was just that maybe CBC's and complete metabolic panels. But as life has gone on testing has gotten more and more complex. For the laboratorians, our kind of third population listening, I'm kind of curious, you mentioned some of these things like, sometimes we call something a confusing name, things like that.

What's your advice to the laboratory professionals that are listening about how we can be, how we can detect when these kinds of things are going awry or how, how do you keep your finger on the pulse of, how your colleagues on the clinical side are using your tests? - Yeah, no, it's an excellent question and a hard one to answer, honestly, I think really looking at utilization patterns can be kind of something that we can use as sort of a flag.

If you have a really high volume of a test that you sort of aren't expecting, or maybe you're spending a lot of money sending out a test.

You can start questioning, go to the top users and ask them, what do you do with this result, et cetera, et cetera and ask some of those questions, really, to educate yourself if nothing else.

And then when it comes to actual test naming there are initiatives out there to try and standardize our names for orderable tests so that, the medical student that goes onto a residency somewhere else and then a fellowship possibly somewhere else and then practices medicine at, various institutions, you don't have to relearn medicine, every time you take a step in your career. So actually this is kind of in that informatic space. There's a gal, Dr. Ila Singh, who leads a Truulab.

I'm not gonna be able to tell you what that stands for T R U U L A B initiative, which is actually sponsored by the CDC to help, they're kind of sending out surveys to clinicians and asking them, what would you call this? And then, kind of coming to consensus for some of those things, you'd think it would be simpler than that but it actually isn't. - Oh, that's awesome. That's an awesome thing to mention. I wasn't aware of, of that Truulab, and we're really kind of hip hooking on a lot,

I know we've kind of gone down a little bit of a rabbit hole, but I'm so curious. And I think you were just throwing out these gems for our audiences, clinician, laboratory professional and student, kind of going back to the big picture, what do you kinda see, I know you were interviewed for that article but what do you see as the future for saliva testing like? Is this bright, dim, long road? What do you see?

- Yeah, honestly, I would be only guessing but I'm going to just speculate that saliva testing, it may expand in some of those niche areas, I'll call them. I don't anticipate we're going to be filling our lobbies with saliva receptacles anytime soon, people are still going to be coming for lab venipunctures for a majority of testing. But I do anticipate that kind of home collection genre will expand potentially because I think there is a demand for it.

And companies have tried and failed, but I know that there is significant effort out there by, vendors and other IVD manufacturers to, attempt to have that more less invasive sample collection option and can facilitate the testing that populations want and need. And hopefully improve health and livelihood. - So spittoons are still on the way out but it's certainly, where it logically makes sense for the reasons that you highlighted about timing and ease of use, it's definitely worth exploring.

Thank you for rounding with us Dr. Block. - Yeah. Thank you for having me. This was really fun. - Thanks to our listeners. Thank you for joining us today. We invite you to share your thoughts and suggestions via email. Please direct any suggestions to [email protected] and reference this podcast. If you've enjoyed Lab Medicine Rounds Podcast, please subscribe.

And until our next rounds together we encourage you to continue to connect lab medicine and the clinical practice through insightful conversations.