Doctors Could Use Snot Instead of Blood for Diagnostics—Why Don’t They?
Nasal mucus carries many substances that are also used in blood and urine tests, sometimes in greater concentrations.
I started out researching this article because I thought it would be funny to shine a scientific light on snot. What do the shades and viscosity mean? How do humans produce so much of it?
But as I tumbled down the snotty rabbit hole, things turned out to be more interesting than I could ever have imagined: snot is not only a very active guardian of our airways and an essential part of our immune system, it could also be used instead of urine or blood to painlessly diagnose everything from pregnancy to cancer to multiple sclerosis to diabetes.
That last part is great, but there's a problem: no one is researching the useful possibilities nasal mucus—except for one doctor, who's been researching mucus for decades and tells me snot could be the ultimate diagnostic fluid, ultimately replacing blood, urine, and saliva.
But let's start with the basics. Boogers, snot, phlegm, nasal mucus, or whatever you want to call it, is part of the system that keeps lungs clear of invading microorganisms and other icky stuff. As the excellent Annalee Newitz of io9 wrote, mucus "is an almost magically efficient system for capturing particles entering the nose, and flushing them out quickly."
Most of the "flushing" happens thanks to cilia, tiny hairs that sweep the mucus to the back of the throat, where it drops down and is swallowed into the hellish acidic environment of the stomach for disposal. The average human produces a bit less than a litre of nasal mucus a day, consisting of 95 percent water, 3 percent mucin and 2 percent other stuff, like enzymes and proteins.
The world your snot lives in is our body's first line of defense against all kinds of organisms that want to hitch a free parasitic ride in our warm and cozy bodies. And it's not just an incredibly effective passive filter that catches nearly 100 percent of incoming microparticles.
Researchers at San Diego State University discovered that mucus harbours a completely independent immune system that actively reacts to incoming bacteria and parasites. The mucus layer that lines the nose catches viruses (bacteriophages) that kill bacteria and keeps them there to kill bacteria that get caught in snot. As lead researcher Jeremy Barr told Gizmag in 2013, the bacteriophages in the nose "demonstrate the first symbiotic relationship between phage and animals."
The more I read about snot, the more interesting it becomes. Mucin, which makes up just a small part of nasal mucus, is the substance that makes it viscous, but it's also a very effective germ-repelling substance. So effective that researchers at MIT proposed to use it as a biofilm on medical equipment to keep germs off—as counterintuitive as coating sterile equipment with the main ingredient of snot sounds.
"The collection technique is simple and the analytic tools for measurement are very straight forward"
Mucin is also being researched as a marker for a plethora of diseases. You've almost certainly experienced one of these: during a common cold, nasal mucus gets more viscous and sticky because of overproduction of mucin. The yellow or white color of your boogers is because of the large number of white blood cells that are being produced to fight off the disease.
Increased mucin production is also associated with the occurrence of different kinds of cancer: lung, breast, pancreas, ovary, colon and more. And this is where it gets even more interesting, trust me.
Nasal mucus is an integral part of your body's immune system, so in principle it can be used to diagnose different types of diseases that make the immune system kick into action, just like blood.
Dr. Robert Henkin of the Taste and Smell Clinic in Washington DC has studied taste and smell disorders for over 40 years and as such is no stranger to snot. He is a lonely pioneer in the field of using snot to diagnose disorders, and claims that nasal mucus could be used as a non-invasive diagnostic and prognostic fluid for many diseases.
"Nasal mucus is a polyfluid that relates to all kinds of physiological problems: diabetes, multiple sclerosis, embolism. The big difference is that you don't have to dig in to get it," he tells me on the phone. "Nasal mucus is a bodily fluid, all the major proteins can be found there. It doesn't only protect the body, it manifests it as well. Anything you can tell from blood, you can tell from nasal mucus."
Dr. Henkin first became interested in analysing the content of nasal mucus while researching ways to diagnose different kinds of olfactory disorders in people who lost their sense of smell. But when his team started analysing, they found a lot more than they expected.
A complete nasal mucus analysis by Dr. Henkin and colleague Irina Velicu revealed that nasal mucus carried many substances that are also used in blood and urine tests, sometimes even more pronouncedly. They found, among many other things, that the same proteins that are detected in blood to predict preeclampsia in pregnant women could also be found in nasal mucus.
In some cases, proteins were found in nasal mucus that couldn't be found in blood or urine. I won't bore you with the details (you can read up on it here), but certain indicators associated with colorectal cancer were found in mucus but not in blood. "In blood you might not have all the acute changes so readily available. Nasal mucus allows for diagnosing both acute and chronic illness," Dr. Henkin tells me.
So, if snot is such a wonderful way to see what's going in the body, why aren't we using it?
On top of the sensitivity and usefulness for diagnosing a huge variety of illnesses, the biggest advantage of using snot is that it's so readily available. There's no need for needles, no need for collection cups for urine; just take a swab of boogers and analyse it. According to Dr. Henkin, it's a very fast and easy way to get an idea of someone's general health.
"We collect nasal mucus by having the patient blow their nose into 50 ml plastic tube, just as they would into a handkerchief," Henkin tells me. The mucus in the tube is centrifuged and analysed with a spectrophotometric immunoassay to check its contents. The technique is extremely sensitive, according to Dr. Henkin, and works with microgram quantities of mucus. All in all, "the collection technique is simple and the analytic tools for measurement are very straight forward."
So, if snot is such a wonderful way to see what's going in the body, why aren't we using it? Dr. Henkin tells me that it's mostly a problem of awareness. Doctors learn about blood, urine, and saliva tests in their textbooks, but not about the possibilities of nasal mucus. Which is probably also the reason that he's practically the only person researching this—researchers just don't know there's a whole world of possibilities literally in their faces.
Dr. Henkin tells me that there might be a number of other reasons why nasal mucus isn't being used yet. First of all, the technique Henkin used to analyse the snot is "clinically useful but not a major component of many physicians' experience or laboratories, although present in all pathological laboratories."
On top of that, standards must still be established for many analyses, although some standards have been explored and published by Henkin and his colleagues. "In this sense reviewing my work becomes a standard upon which others can go forward," he says. Now hopefully, "others will follow and do more work to utilise this biological fluid to diagnose pathological and physiological processes."
And that's how a silly article about snot suddenly turned into a call for more research into snot. Oh, and in case you were waiting for some answers to the questions in the first paragraph: at the very least, eating boogers is not harmful, since you swallow most of your mucus anyway; you can check what the colors of you snot mean in this nifty infographic; and, just like the human body, it consists mostly of water so we can produce lots and lots of it very quickly.
This article was translated from Motherboard Netherlands.