Allergy testing for pets: Beyond the food trials and tribulations and onto the big guns
Got an itchy pet? Losing hair? Diagnosed with “allergies” or “allergic skin disease”? Are the summer months causing your pet especial distress? Then you’ve likely been offered “allergy testing.” But what, exactly, does that mean?
For starters, it means we rule out all other potential causes of skin disease to make sure we’re not all hung up on the allergy thing for no good reason. This includes serial skin scrapes to look for bugs, superficial skin cell testing (cytology, usually via “impression smears”), ear swabbing for cytologic (cell) evaluation and cultures and blood testing––typically for hormonal diseases (like Cushings or thyroid disease). For some kinds of lesions, skin biopsies are sometimes in order as well.
Then we go for basic palliative care to see what tends to work. What’s the response to shampoos, dietary supplements judiciously chosen drugs (like antihistamines, steroids, flea meds, other insecticides, cyclosporine, antibiotics, antifungals, local treatments, etc.)?
So you know, this isn’t necesarily done just to take the easy way out. Response to treatment can be a significant indicator of what’s up with the skin. It can also power you through the short seasonality of your pet’s problem––if, indeed, it’s seasonal.
Next up, we’ll try food trials to determine whether one or more proteins and/or carbohydrates are stimulating the immune system at the level of the skin. Here’s a complete post on this.
Once all this has been accomplished, we may recommend you see a dermatologist for allergy testing. Sometimes we’ll recommend a dermatologist even before all this intensive testing. For my part, I tend to refer to a dermatologist when the problem is severe and/or intractable and if I’m uncomfortable with or confused by the test results or a pet’s clinical response to treatment (which happens with occasional regularity).
At this point, we can elect to go one of two ways: Depending on your pet’s response to treatment and your comfort level with drug therapy (and its expense) we can either choose to stick to what we know already works or we can move on further testing.
Here’s where things can get tricky. It’s ime to bring out the big diagnostic guns: skin testing and/or blood testing to determine which specific allergens are causing the problem. This is most helpful for inhalant allergies (also referred to as “environmental” allergies, “seasonal” allergies or “atopy”). Food allergens may be tested, too, but these tests are very insensitive and non-specific relative to inhalant allergen testing.
In fact, recent studies show that food allergy testing through skin or blood can be downright wrong (and, frankly, inadvisable), which is why we like to stick to well-run food trials for food allergies.
Some vets use skin testing (dematologists, usually, since these are expensive to maintain in house) some use blood testing (as I do when I haven’t referred to a dermatologist) and some use both, knowing that both tests have their limitations.
If you’re like most of my clients, you’ll think it a bit above-and-beyond-ish to test your pet for allergies in the way we do for humans. It’s expensive to have skin tests performed. It’s also pricey (though usually less so) to go for its alternative: blood testing.
Skin testing: $500 to $1500, depending on the number of allergens tested and the priciness of the hospital. Blood testing (or “serology”): $100 to $800, depending on the same above factors.
Nonetheless, a pet’s allergic skin disease is often severe enough to warrant these advanced tests. (I perform about one to three every month).
Problem is, pricey as they are, they’re not perfect. Though they grant you a formidable glimpse into the categories of allergens that are most responsible for a pet’s individual allergic profile, they’re “off” in many cases. Here are some limitations:
For both kinds of skin testing, pets must be off all immune system-affecting drugs for six weeks. That means no steroids, cyclosporine or antihistamines (though antihistamines may be continued up until one week before testing). No changes must be made in the animal’s basic routine (feeding, environmental exposures, etc.)
Moreover, even when we think everything’s well controlled in the pet’s environment (same food, same shampoos, same everything), pets can have different immune responses to allergens on different days or different times of the year. Stress can interfere with responses, too.
For skin testing, veterinarians clip the fur, inject a small amount of each of up to 50 allergens into the skin and record the size of the swelling (indicating the immune response).
The problem is that different vets will have different ideas as to what constitutes a high or low degree of skin response. Human error and inconsistency, even on the same patient, is always a factor.
For blood testing, the issue is that different labs will come up with different results. Blood handling, human error, allergen purity, etc. can all interfere. For that reason, dermatologists often claim these tests are poor substitutes for skin tests. The skin test is the “gold standard” because it’s carefully controlled by a specialist.
And I would tend to agree. Nonetheless, I’ve had great results on the many blood-based allergy tests I’ve performed. My local dermatologist, Dr. Millie Rosales, concedes that she sometimes uses serlologic testing, too, and that certain labs seem to produce excellent results––results comparable to skin testing. Still, all allergy tests––skin or blood-based––need to be taken with a hefty grain of salt.
So why go through with it at all? What does it help to know what you pet is allergic to? For two reasons:
Because knowing what’s causing the problem can help you avoid some of them. Sure, you won’t be able to avoid pollens, but wool, jute, cotton and fleas? Your knowledge of their allergenicity can make a huge difference to how carefully you approach these substances. Because we can always formulate a custom-made vaccine against the allergens your pet can’t avoid (molds, trees and grasses, for example), this is an excellent option––if you’re willing to assume the additional expense and the work required by regular allergy shot administration.
It may sound like a lot of work, these allergy shots. But they’re really not. Subcutaneous injection is easy in pets. We can teach you how to have it done. And we’re always happy to do them for you if you’re willing to come in on a regular basis (frequently at first then only once a month).
The best part about an allergy vaccine protocol is that no drugs are administered (though many pets may need drugs to remain comfortable until the vaccines kick in). These are natural substances that work because the gradually increased levels of allergens in the shots are helping the body’s immune system become acclimated to them––instead of producing the aberrant immune response responsible for the allergies.
The trouble with this approach is four-fold:
1. Pets can over-react to the increased levels of allergen, resulting in more itching, redness or even anaphylaxis (though this latter issue is rare). In these cases we back down on the rate of allergen increases.
2. Pets can develop allergies to new substances over time, requiring that we re-submit blood samples or re-do skin tests periodically (often every 12 months or so, though some pets may never need a re-test and may even have their vaccines successfully discontinued over time).
3. Some pets (about 40%, it’s estimated, may not respond well enough to allergy shots to warrant the work and expense (about $100 to $500 every 9 months or so).
4. As mentioned before, tests may not provide accurate results––which may account for vaccine failure as discussed in #3.
That’s it for now. Phew! Have anything to add or ask? I’ll take it all up, but give me a few hours to respond, I’m wiped out for the moment.