Grass Allergen Levels Better Measured Through Monitoring Patients’ Hay Fever Symptoms


This research had been conducted to look into prior studies linking daily pollen counts to respiratory allergic health outcomes.

Credit: Pexels

Credit: Pexels

Levels of grass allergen (Phl p 5) are more frequently linked to allergic respiratory symptoms as opposed to counts of grass pollen, according to recent findings.1

These results followed a recent study conducted with the aim of evaluating associations between grass pollen counts and Phl p 5 with the respiratory symptoms observed in adult patients with cases of moderate-severe allergic rhinitis and daily asthma admissions to hospitals.

This new research was led by Elaine Fuertes, PhD, from National Heart and Lung Institute at Imperial College London in the United Kingdom. Fuertes and colleagues explained that symptoms of allergy may be reported even on days that have lower pollen counts, indicating that epidemiologic research based only on counts of grass pollen may be limited.

“Although different groups of allergens related to grass pollen are known to induce IgE responses, we studied Phl p 5, as this is a major timothy grass allergen recognized by almost all individuals with grass pollen allergy, which induces strong IgE antibody responses and clinical allergic outcomes,” Fuertes and colleagues wrote.2

Background and Findings

The investigators looked at data from 93 adult study subjects in 2013 that had moderate-severe grass pollen–induced allergic rhinitis. These individuals had a mean age of 33.5 years, with 66% of them being identified as male and 80% being White.

The subjects were enrolled in the PollenLITE (Pollen Low dose Intradermal Therapy Evaluation) research, the design of which was a randomized, single-center, controlled, double-blinded phase 2 study. The research was carried out at Guy’s Hospital in the UK, with individuals involved filling out diary cards in which they noted their symptoms and medication implementation each day.

The investigators used blood to measure grass pollen group 5–specific levels of IgE. These findings had been used previously to suggest that intradermal allergen immunotherapy was shown to not be clinically impactful.

The research team’s primary endpoint was a combined symptom and medication score, described in their research as the ‘total score.’ The secondary endpoints which had been predefined were subjects’ overall medication scores and their overall symptom scores.

The hospital admissions’ daily counts as well as the emergency department visits related to symptoms of asthma were drawn from Hospital Episode Statistics data held at Imperial College London for the time frame of May - August 2013.

The investigators looked at all age groups. The team used an alternative outcome of emergency department visits related to asthma which had been coded in the first 2 diagnosis fields using the diagnostic code signifying respiratory conditions of bronchial asthma.

The team looked at subjects found within 100 km of their pollen measurement region, calculating daily airborne pollen counts Phl p 5 levels in the air, daily mean temperatures, mean precipitation, and mean relative humidity information.

Overall, the research team reported that there were positive associations seen between the observed daily pollen counts, levels of Phl p 5, and the overall likelihood of there being a high combined symptom and medication health score seen in separate models.

Despite these findings, when the investigators adjusted for both pollen counts and Phl p 5 levels in their mutually adjusted models, they found that the links continued to be substantial for Phl p 5 levels (odds ratio [95% CI]: 1.18 [1.12, 1.24]) although the pollen count associations had been substantially attenuated (odds ratio [95% CI]: 1.00 [0.93, 1.07]).

They noted that, interestingly, similar trends were not shown to have beem observed for asthma hospital admissions found in London.

“High pollen season can be serious for people who suffer with hay fever, and can trigger severe asthma attacks in those who are allergic to grass pollen,” senior author and professor Stephen Till, from King’s College London, said in a statement. “This study shows there is a superior way of measuring pollen allergens in the air than the traditional pollen count.”3

Till added that monitoring grass allergen could allow individuals with serious allergies to be better prepared in the upcoming pollen season.


  1. Fuertes E, Jarvis D, Lam H, et al. Phl p 5 levels more strongly associated than grass pollen counts with allergic respiratory health. J Allergy Clin Immunol. Published online November 22, 2023. doi:10.1016/j.jaci.2023.11.011.
  2. Characteristics and immunobiology of grass pollen allergens. Int Arch Allergy Immunol. 2003; 130: 87-107.
  3. Measuring grass pollen allergens instead of grass pollen count will help hay fever sufferers. King’s College London. January 8, 2024. Date accessed: January 8, 2024.
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