Grass pollen allergy and cross-reactivity: A component-resolved case study

Seasonal respiratory symptoms can be difficult to assess, especially when multiple sensitizations are involved. The key question is which sensitization is clinically relevant and driving the symptoms.

Identifying whether sensitization is primary or cross-reactive helps identify the offending allergen and guide allergen-specific management, including avoidance and immunotherapy.¹

This illustrative case study shows how ImmunoCAP™ Specific IgE tests, including allergen component testing, help clarify the cause of symptoms and support appropriate referrals and next steps in patient management. This enables more confident, targeted treatment decisions.

The primary care provider completes a clinical history and physical examination and orders ImmunoCAP Specific IgE tests. Where appropriate, testing may include allergen components to further clarify the sensitization pattern.

Patient history

Family history

• Atopic mother

Paul's personal history

• Diagnosed with egg and milk allergy at 12 months
• Eczema in infancy
• Mild to moderate seasonal rhino-conjunctivitis from age 8
• Previously diagnosed with pollen sensitization

Paul’s previous primary care provider recommended that he use oral antihistamines and intranasal corticosteroids during pollen season. 

ImmunoCAP Specific IgE test results

Test results should be interpreted alongside clinical history to guide diagnosis and management.² Blood-based specific IgE testing can be particularly useful in settings where skin prick testing is not readily available.³

Whole allergens show sensitization to grass pollen, birch, and several plant-based foods.

Allergen component testing shows elevated IgE to Phl p 1 and Phl p 5b, which are specific to grass pollen. Elevated IgE to Phl p 12, a cross-reactive component, is also present.⁴

Differential diagnosis and clinical relevance of sensitization

The significant IgE levels to the grass-specific components Phl p 1 and 5b indicate primary grass pollen sensitization. Paul’s IgE response to profilin explains the cross-reactivity with multiple fruits and vegetables, consistent with a pollen-food allergy syndrome (PFAS), which typically presents with mild, localized oral symptoms rather than systemic reactions. ⁴

This distinction helps to identify the main triggers and supports the selection of appropriate allergen immunotherapy.

Refined diagnosis

• Primary Timothy grass pollen allergy with profilin-related cross-reactivity (PFAS)

Management plan

• Discuss management of PFAS symptoms, including that reactions are typically mild and localized. Patients may tolerate foods in different forms, such as cooked or peeled, or in smaller amounts. Shared decision-making can help determine when avoidance or modification is appropriate.
• Consider referral to a specialist for further evaluation, including assessment for AIT.

Follow up

• After two years of AIT with his allergologist, Paul’s pollen symptoms improved significantly.
• Food-related symptoms also improved.
• Ongoing monitoring can help assess response to treatment and guide future management.

Clinical impact: Improving diagnosis and risk assessment

This case demonstrates how ImmunoCAP Specific IgE tests, including allergen components, can help identify the primary trigger and distinguish it from cross-reactivity.¹ By providing deeper insight into sensitization patterns, test results can support a clearer understanding of the underlying cause of symptoms—beyond symptom management alone. For primary care providers, this enables more confident diagnosis, informed treatment decisions, and appropriate referrals. With the right information, providers can act earlier and guide patients toward more targeted care.

The people, places, and events depicted in this case study do not represent actual patients and are not affiliated with Thermo Fisher Scientific.