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Reinventing The Wheal: Why Allergy Scratch Testing Has Become Obsolete

Posted by Alex Metarelis on Aug 10, 2018 10:38:35 AM

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Imagine this: "We don't know if you're allergic to any of these elements so let's give your skin a dose of everything and just see what happens." Take a step back and listen to how archaic this sounds. The pain induced during skin prick testing, the risk of severe reaction to the patient, the time wasted with each individual scratch - and it's still utilized today!

Skin prick testing for allergies is painful, time-consuming, and somehow still considered the traditional method for doctors across the nation. Here's why IgE (Immunoglobulin E) blood testing for allergies is diagnostics' way of saying, "Out with the old and in with the new!" 

Inaccuracy of Results

Even with the pain administered and time taken on skin prick tests, one would think the silver lining would be accurate test results. The triple whammy in all of this is the wheal-and-flare size on the skin is not a true predictor of illness severity, in a study performed by The American Journal of Rhinology & Allergy. If patients had raised red bumps after scratch testing, that did not necessarily specify how allergic they were to the allergen. Allergies that were anywhere between near-absent to highly severe could have equal-sized reactions on the skin.

One Stick vs. Multiple Sticks

With IgE allergy testing, only one needle stick, a couple tubes of blood, and 5 minutes of time are needed to diagnose for 71 different allergens at Elite Medical Laboratory. Consider this as opposed to skin prick testing, which is many scratches from different antagonists, waiting 15-20 minutes after for red bumps to show on the skin, and the patient dealing with itching discomfort the next few hours - all for results with questionable accuracy.

Realistically, how many more patients could be seen per day if a faster, more reliable blood draw process is adopted into a clinic? Twice? Three times as many? If you're running a clinic, that's money left on the table.

Patient Safety

It is safer for patients with heart or lung conditions to have their blood drawn, as skin prick testing may cause systemic reactions and even trigger anaphylaxis. With skin prick testing, patients are ordered to cease taking antihistamines and cold medicines up to a week before the procedure. Good news with IgE blood testing is patients can continue taking these medications up until blood draw, with no interference in resulting. 

RAST: Not The Only Blood Draw Method

Not all allergy blood draw options are the RAST method. RAST (in its original meaning) is a limited, inaccurate panel and is rarely used to this day. In fact, the methodology has evolved over time:

  • RAST (Radioallergosorbent test) in the 1970s
  • ELISA (Enzyme-linked immunosorbent assay) in the 1980s
  • ImmunoCAP in the 1990s
  • 3rd Generation Allergy Testing Method in the 2000s to now

3rd Generation Allergy Testing is the most advanced at this point in time, as it determines allergen-specific IgE at extremely low levels with excellent accuracy. RAST is in the past, but the brand name is often used in place of the general method of allergen blood testing, just as the word "Xerox" gets used in place of making printer copies or saying "Hand me a Kleenex," rather than a tissue. 

Reinventing the Wheal

If you're a healthcare provider who has performed allergy scratch testing, you might question the difference in test resulting between scratch and IgE. We have developed our own Scratch-To-IgE Conversion Chart which shows IgE Range in the allergy blood test results compared with skin wheal-and-flare sizes in scratch testing, and matching to appropriate allergic classifications (absent, very low, low, moderate, high, very high). 

The Bottom Line

Many healthcare professionals' biggest concern with blood testing for allergies is that it takes days or even weeks to get results back, which may be true for most labs. However, Elite Medical Laboratory performs 3rd Generation Allergy Testing on 71 different allergens and typically reports within 24-48 hours of sample reception. 

Download Our Scratch-To-IgE Conversion Chart

Topics: Blog