Grass pollen allergy (IgE timothy grass)

Timothy grass (Phleum pratense) is a common grass in meadows and roadsides. The pollen of different grass species is very similar, so the result for timothy grass usually also says something about grass pollen in general. This test measures the amount of IgE antibodies against timothy grass pollen in the blood, in kU/l. IgE is the type of antibody that, in an allergic reaction, triggers mast cells to release histamine; the body only makes these antibodies after it has previously been in contact with the allergen, and this is called sensitization.

• Sensitization to grass pollen: the body has made IgE antibodies against timothy grass pollen
• Support in working out suspected hay fever from grass pollen, together with the history of the symptoms

The GP mainly looks at the history: in which months and where the symptoms occur. With a positive result and matching symptoms, advice follows to reduce contact with pollen, such as keeping windows closed on dry, sunny days, and if needed medication for the nose and eyes. With a lot of symptoms despite medication, an allergist or ENT specialist can discuss immunotherapy, where the result for single allergens helps determine which pollen it targets.

A positive IgE result shows sensitization, not allergy: it only says that there are antibodies, not that you get symptoms from them. The Dutch medical specialists' guideline (FMS) on upper airway allergy says this literally and recommends choosing a test for single allergens based on the history of the symptoms; the result therefore only means something if it fits when and where you have symptoms. With grass pollen, the season is an important part of that history: symptoms that fit the flowering of grasses make a positive result more meaningful. A positive result without symptoms is not treated.

• Sensitization without symptoms is common; the result can only be interpreted together with the history of the symptoms.
• Grass pollens cross-react strongly with each other; the test does not show which grass species you react to, and a positive result for rye often goes together with a positive result for timothy grass.
• The result says little about the severity of the symptoms; a higher value does not automatically mean more trouble.
• Laboratories use different measurement methods and cut-off values; results from different labs cannot be compared one to one.

Hay fever is common and often starts at a young age. According to the Longfonds (Dutch lung foundation), the grass pollen period from May to August is the period with the most symptoms for many people. Sensitization is more common than the allergy itself.

Useful with symptoms of the nose, eyes or airways that come back every year in late spring and summer, especially outdoors on dry, sunny days. The result then helps determine whether grass pollen may be the cause. In people without such symptoms, the test adds nothing: sensitization without symptoms is not a disease and is not treated.

• A positive result without symptoms can cause unnecessary worry or unnecessary measures, while sensitization without symptoms does not need treatment.
• A normal result does not rule out symptoms in summer; other pollens and non-allergic causes also cause nasal symptoms.

• NVKC, allesovertesten.nl: Allergie (RAST)
• FMS Richtlijnendatabase: Allergie van de bovenste luchtwegen, module Aanvullende diagnostiek
• Thuisarts.nl: Ik heb hooikoorts
• Longfonds: Hooikoorts