Updates urged to 'arbitrary' uniform specific IgE cutoff

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By Anne Harding

NEW YORK (Reuters Health) - There is no single cutoff for specific IgE (sIgE) that indicates clinically relevant sensitization to aeroallergens, a new study shows.

"The current cut-offs for sIgE . . . are arbitrary and not necessarily associated with clinical symptoms. Therefore, is it important to be cautious in the interpretation of a positive result, as it is often not related to relevant symptoms," Dr. Ann-Marie Malby Schoos of the University of Copenhagen, the study's first author, told Reuters Health by email.

The uniform cutoff indicating sensitization of 0.35 kUA/L is based on the detection limit of early assays, Dr. Schoos and her team note in JAMA Pediatrics, and has "limited clinical relevance and little concordance with the skin prick test." The detection limit of newer assays is 0.1 kUA/L.

The authors looked at the distribution of sIgE levels to house dust mites (HDM), cat, dog, grass and birch in 835 six-year-old participants in the Copenhagen Prospective Studies on Asthma in Childhood.

The median value for children with detectable levels was 0.14 kUA/L for HDM, 0.06 kUA/L for cat, 0.07 kUA/L for dog, 0.33 kUA/L for grass and 0.20 kUA/L for birch.

Among children who had allergic rhinitis (AR) to an allergen, median sIgE was 6.29 kUA/L for HDM, 1.41 kUA/L for cat, 5.73 kUA/L for dog, 2.43 kUA/L for grass, and 1.97 kUA/L for birch. There were overlaps between symptomatic and asymptomatic children, the authors found, and some children without AR nevertheless had high sIgE levels.

Studies seeking to identify sIgE cutoffs for food allergens have also found higher limits predicted clinically relevant sensitization, with variation across allergens, Dr. Schoos and her team note. They conclude by calling for updated cutoffs for accurately predicting clinically meaningful sensitization.

This could be done by looking at sIgE in a large group of patients with doctor-diagnosed AR, Dr. Schoos noted. "We would like to do a study across different cohorts, to be able to evaluate meaningful cut-offs based on the specific IgE levels and doctor-diagnosed allergic rhinitis."

Dr. Hugh A. Sampson, a professor of pediatrics at the Icahn School of Medicine at Mount Sinai in New York City, told Reuters Health by phone, "What they're showing is that simply having the Ig in a low level doesn't mean in any way that you're going to be sensitized. You can't take a single value and say it's the same for all the different allergens."

Clinicians need to look beyond a "positive" test from a lab, based on the uniform sIgE cutoff, he added, especially when a panel of tests is ordered.

The levels identified in the current study can help clinicians to determine whether a patient's clinical symptoms are due to the allergen, or if the patient is simply sensitized, Dr. Sampson said. "You really need to be taking into account the quantity when you're thinking about clinical symptoms."

SOURCE: https://bit.ly/2WNTocS JAMA Pediatrics, online May 18, 2020.

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