Do-it-yourself lab tests aren’t always a good idea

The Pediatric Insider

© 2015 Roy Benaroch, MD

Labcorp, one of the largest outpatient lab providers in the USA, is soon going to let you skip the tedium of a doctor’s visit to get lab work done. Want some tests? Come on down!

I’ve got mixed feelings about this. While there are some tests that seem reasonable for people to do on their own—pregnancy and HIV tests come to mind—others may lead to problems. The bottom line: people imagine tests are simple things that give you a reliable, yes or no answer. In reality, many tests are far from perfect. And their results might be more misleading than accurate.

First, the good tests. A urine pregnancy test is safe and easy to do, and very accurate. If you’re more than a few days late for your period, and your pregnancy test is positive, it’s time to think about buying little booties. Likewise, even the (relatively) cheap drug store saliva HIV tests are really quite accurate, almost all of the time—though even then, the test doesn’t become accurate until several weeks after HIV infection. A drug store test done a few days after a potential exposure tells you nothing.

But many other tests are far more complicated. There are all sorts of “thyroid tests” that can be done, but (for example) thyroid antibodies are often positive in people who don’t actually have thyroid disease. Likewise, antinuclear antiobodies (ANA), which you’ll find on the internet is a “lupus test”, are very often positive in people without lupus.

Allergy blood tests are even more problematic. A recent study showed that even among those with a positive food allergy blood test, only 2.2% actually had a food allergy. If you do big panels of food allergy tests, at least some of them are going to be positive in anyone—that’s just the nature of that kind of test. That’s why allergy testing is such a bad idea, unless there’s a specific clinical indication.

Many tests are for screening, rather than diagnosis—and I think that’s going to lead to misunderstandings, too. The “prostate specific antigen” test can be used to screen for prostate cancer—but many men with a positive test don’t actually have cancer. To complicate things further: many men who do have prostate cancer will not be affected by it—they’ll die of something else long before the prostate cancer causes mischief. Prostate cancer can be a terrible problem, especially in younger men, but appropriate screening for it involves more than just getting a blood test.

Celiac disease affects about 1 in 100 people, but testing for it can be complicated. The genetic test for the two celiac-associated haplotypes is almost always positive in people with celiac disease… but most of the people who test positive for that will never develop celiac. In other words, a negative tells you something (you’re unlikely to ever get celiac), but a positive tells you nothing (you may or may not currently have celiac, and you may or may not ever develop it.)

Tests for Epstein-Barr virus and Lyme disease–these have been misunderstood by doctors and laymen for years. Is Labcorp going to explain what the results mean in a way that their customers understand?

I’m also troubled by the marketing of these tests by a for-profit company. Traditionally, doctors who order tests don’t make any money off of them—there’s no conflict of interest. Once Labcorp is profiting off more and more tests, won’t the logical next step be to market them more heavily? It’s already happening, in my neighborhood, especially with allergy testing—Labcorp really wants me to order more. What happens when they skip me and market straight to you?

We’ll see soon enough. According to the story, Labcorp sees big growth in direct-to-consumer labs. They say this will help people stay healthier and more well-informed. It’s certainly profitable for them. With the internet, as we all know, everyone is an expert, so it’s logical to figure that people who order tests on themselves know what they’re doing. Right?

Food allergy testing: Do those big panels work?

The Pediatric Insider

© 2014 Roy Benaroch, MD

Theresa asked about eczema (see last post), and also asked about food allergy panels. Does all of that testing help?

Well, usually, no.

It turns out that allergy testing (whether done by skin scratches or blood tests) doesn’t even test for allergy. We sort of smudge through that distinction, because it’s complicated. But it’s time for someone to spill the beans about this kind of testing, and here at The Pediatric Insider, we’re all about telling you guys “the real deal”—the inside info that docs typically keep to ourselves. Here’s something you may not want to hear: “allergy” testing is, well, just not very good.

Let’s start basic. An “allergy” is an adverse reaction (a bad thing, some kind of symptom) triggered by an exposure to something, and caused by a reaction of the immune system. It requires symptoms of some kind, and requires the symptoms to be caused by an immune reaction of some sort.

A broader term, “adverse reaction,” includes allergies but also non-immunologic reactions to things. For instance, many people get bloaty and gassey after ingesting milk. That’s typically caused by lactose intolerance, an inability to digest milk sugar that has nothing to do with any allergy. Still, lactose intolerance and gluten sensitivity and many other reactions are sometimes lumped in with allergies. They’re not allergic, and no “allergy testing” of any kind could possibly identify non-allergic reactions.

Also, allergy – an allergic reaction – requires some kind of symptom, and the symptom ought to be reproducible after exposures. Allergy “testing” often reveals “positives” to foods or other things that upon exposure doesn’t actually trigger a reaction. If eating a food you’ve tested positive for doesn’t cause a reaction, you are not allergic to the food. Period. Allergy requires symptoms.

And that’s the biggest issue with allergy testing—because these tests don’t test for allergy. They test for “sensitization”. They show that your immune system has the capacity to react to the substance, but that doesn’t necessarily mean that you will react to the substance.

I can’t tell you how many times I’ve heard from families who tested positive for food XX, though they’ve never had a reaction to XX—and in fact, they used to eat XX all the time. If your child eats peanuts routinely and doesn’t have a reaction, it doesn’t matter what the allergy testing shows. He is not allergic. The test shouldn’t have been done in the first place.

There are other problems with allergy testing. Though individual tests can fairly accurately say who is sensitized, each test does have a chance of a false result. If the rate of an incorrect test is, let’s say, 5%, that might sound pretty good. But what if you do a panel of 40 foods, each of which has a 5% chance of a false result? There’s a 88%* chance you’ll get at least one false positive. If the panel is large, you’re going to get false results. The larger the panel, the more wrong answers you’ll get. What then?

Another problem: there are a lot of ways to do allergy testing, and they’re not all the same, and I most families have no idea what they’re getting into. The current, most reliable blood testing for sensitivity is called a Cap-RAST or ImmunoCap, and it tests for specific IgE molecules. Older tests are far less accurate, and some still in wide use are as worthless as flipping a coin. If you are going to do allergy testing, you should at least do the best one. Skin testing, too, has different reagents and methods, and it can be difficult to know if what’s being done is the most-reliable testing.

About skin tests: they’ll be unreliable if the patient has been taking antihistamines, and they’ll be less reliable if the patient has a skin condition like eczema, which causes high overall IgE levels and a sort of overall hypersensitivity that leads to many false positives on both skin and blood testing. Testing children with eczema is fraught with peril, which is one reason many dermatologists aren’t keen on addressing the possible allergy-eczema connection.

Still, allergy testing can sometimes help, if you keep these points in mind:

• Consult with a board-certified, genuine allergist. Many companies market allergy kits and tests and things for general practitioners and ENTs and who knows who else. They’re a big money maker, but we really don’t know what we’re doing with them or how well they work. Please stay away from alt-med practitioners who claim to be able to diagnose allergies by holding your hands or waving vials about or using some kind of elecromagnetic hyperscience quantumconfusionating walletemptier.
• Test only for foods or other allergens that might be causing a reaction. Foods that are eaten routinely without problems are NOT allergies (and testing will lead only to confusion); foods that always do cause a reactions ARE allergies, and don’t have to be tested. Only test the grey-zone, “maybe” foods, or you’re asking for trouble.
• Test a limited number of foods. Almost all food allergies are to a small number of candidates: milk, egg, wheat, soy, shellfish, fish-fish, peanuts, and treenuts. Tests for mustard and plantain and okra and lamb are unlikely to yield useful results, and might upset the lambs.
• Think of allergy testing as a starting point, for clues to what might be a real allergy (positive tests), and clues for what are probably not causes of allergy (negative tests.) Under most circumstances, unless there’s been a life-threatening reaction, you have to confirm ‘allergy testing’ with deliberate exposures. And if there has been a life-threatening reaction, you probably already know what the trigger was—so why do the test?

* It has been a long time since I did statistics. What I did was figured the 5% chance of a false result on one test means that 19/20 times the test will be correct. So if you’re doing that 40 times I figure the chance of 40 correct tests in a row is 19/20 raised to the 40^th power = ~ .12, and the chance of that not happening is 1-.12 = 88%. Am I even close? At The Pediatric Insider we welcome comments that point out boneheaded mistakes. Be gentle.

Allergies and eczema: Are they related?

The Pediatric Insider

© 2014 Roy Benaroch, MD

Theresa wrote in, “I’d be interested in seeing an article about the connection (or lack thereof) between food allergies and eczema. Also interested in the helpfulness (or lack thereof) of large blood panels for food allergy testing.”

Two good topics—and I’ll get to food allergy panels in the next post. First: What’s the connection between allergies and eczema?

Eczema is by far the most common chronic skin condition pediatricians see. It’s present in about 1 in 3 young children, or maybe more if you count the milder cases. In fact, if you look closely enough, just about every child has at least some eczema. It’s usually mild, and improves nicely with good skin care and the occasional use of low-strength topical steroids.

What causes the itchy, scaly, red rash? Many things seem to contribute: dry skin, rough fabrics, and scratching all make eczema worse. It often runs in families, and often occurs in the same children who later go on to have allergic rhinitis (hay fever), asthma, and food allergies (those conditions, as a group, are called “atopic.”) Eczema is also called “atopic dermatitis”—atopic referring to inflammation and sensitivity, typically caused by an allergic trigger. These conditions are all interrelated, and often co-exist. So is eczema, the rash, caused by a specific, identifiable, and avoidable allergic trigger?

There’s the controversy.  If you ask allergists, they’ll say “probably yes.” They stress identifying and avoiding specific triggers, typically one or more foods. Sometimes their advice is guided by allergy testing, or sometimes just by history, and sometimes by trial and error. Just avoid food X, and if that doesn’t work, avoid food Y. If there is an allergic food trigger, it’s probably one of the common food allergies, like egg, milk, wheat, soy, fish, or peanut. Maybe try avoiding those.

But it’s hard to avoid all of those foods—and “testing” will often lead to false positive or negative results. If food allergy does trigger eczema, it does it slowly, so it may take several days or weeks of restrictions and reintroductions of multiple, overlapping foods to figure this out. Meanwhile, Junior is still itchy. So the dermatologists take a different approach.

If you ask dermatologists if eczema is caused by food allergy, they’ll say “probably no.” They stress taking care of the skin (using good bathing techniques, moisturizers, sometimes topical antiinflammatory medications, and sometimes agents to reduce bacterial colonization.) Just treat the skin, that’s the dermatologists’ motto. We can make this better, and quickly, without anyone going hungry.

Now, if you ask pediatricians if food allergy causes eczema, we’ll say “sometimes.” Though some of us are probably more allergy-focused than others, most of us probably favor practical advice: for mild-to-moderate eczema, it’s usually best to focus on good skin care, and treat the eczema, and get Junior feeling better. IF initial, safe therapy doesn’t work, or if the eczema is severe, then we’ll also try to identify food triggers—though we’ll keep up the good skin care at the same time. One approach doesn’t mean you can’t also follow the other. And, in fact, the best dermatologists and allergists will also recommend this kind of middle-of-the-road, practical advice.

What about those food allergy panels Theresa asked about? Short answer: They don’t work, at least not if your goal is to figure out what your child is allergic to. More in the next post.

Allergist, nutritionist or dietician?

The Pediatric Insider

© 2012 Roy Benaroch, MD

Anthony wrote in, “My son has a lot of allergies, and I’m not sure what is safe to feed him. Should I see an allergist or a nutritionist?”

Anthony, the first step is to figure out exactly what foods are truly allergic triggers. Many people have the impression they’re allergic to things for a variety of reasons, but they really aren’t. The best way to know for sure is by the history– what reaction occurs when your son eats that food? Though allergy testing is available, it isn’t exact, and doesn’t always show what the true allergies are. Even people who test positive for allergies might not really be allergic.

However, if your son really has food allergies, it is important to avoid those food triggers. You should work with either a pediatrician or allergist to determine what foods need to be avoided. There seem to be many “alternative practitioners” in the world of allergy these days, and they sometimes offer non-standard or genuinely quacky testing. Beware. Work with someone who’s board-certified and knows what they’re doing. Your pediatrician should be able to offer you a referral.

Kids with multiple food allergies can be challenging at mealtimes. If you’re having trouble coming up with a good, well-balanced, and safe diet, working with an expert in nutrition is a very good idea. Again, you need to be careful. A “nutritionist” can be anyone. That word doesn’t have any legal meaning, and there are no educational requirements or certifying authority for nutritionists. Basically, anyone can call themselves a nutritionist, and some of them may have no idea what they’re talking about. A genuine authority on feeding and nutrition is called a “dietician”. Requirements vary by state, but to call yourself a dietician means that you’ve met educational and practice guidelines. Working with a dietician is a very good idea for families with kids who have multiple allergies or other dietary issues. Working with a nutritionist may be a waste of money, or worse.

Allergies without allergy

The Pediatric Insider

© 2011 Roy Benaroch, MD

“My ten year old daughter seems to have allergies—she sneezes a lot, and is always congested. She’s been tested for everything and isn’t allergic. What is going on, and how can I help her?”

No one can be allergy tested for “everything.” With skin testing, there’s only so much skin to use to test; and for blood testing, well, even a vampire can only get so much blood out of a child. Allergy testing uses a panel of common allergens for the area, but can’t possibly cover all possibilities.  It may be that she really is allergic to something, but she wasn’t tested for it.

It’s also possible that the test itself didn’t give an accurate answer. Allergy testing isn’t close to 100% correct, and both false positives (the test is positive, but the child really isn’t allergic) and false negatives (the test is negative in a truly allergic child) do occur. Even though she’s been extensively tested, it could also be that the test is wrong, and she is allergic to something that she tested negative.

There are other things that might be going on, besides allergies. Cold viruses can trigger an itchy or runny nose, so if she’s been getting one cold virus after another it can seem like one long illness. There’s also a non-allergic condition called “vasomotor rhinitis” which causes nasal congestion and sneezing, especially in bright sunlight. Noses can also be bothered by cigarette smoke or other irritants, triggering allergic-like symptoms, without actually causing true allergy. Rarely, an anatomic obstruction like a nasal polyp may cause symptoms similar to chronic allergies.

It can sometimes be tough to tease these situations out. Often, a best next step is to try regular use of an effective allergy medication, even though she tested negative. The most effective allergy medicines are topical prescription nose sprays (do NOT regularly use an over-the-counter medicated nose spray—they’re addictive.) If allergy medications work,  at least she’ll get some relief. You can also try to rinse her nose out with gentle saline solution, which may relieve symptoms caused by irritation (warning: some kids do not like to have their noses rinsed out. Imagine that.) Further discussions and evaluation by an allergist, pediatrician, or ENT (ear-nose-throat) specialist may also be helpful if her symptoms continue to bother her.