Hay fever test: which blood test confirms a pollen allergy

Mid-May, the grass pollen count climbs, and you have taken a tablet every morning for three weeks. It works well enough. Yet you still have no idea what you actually react to, and that is exactly the question a hay fever test can answer.

The free quizzes at the top of Google do not answer it. They ask about your symptoms and end at "you probably have hay fever". What the confirmatory test measures afterwards is never mentioned.

My opinion: those quizzes are built by the companies selling the tablets, and they stop precisely where a real answer would begin.

How can you test whether you have hay fever?

A quiz suggests, a test confirms. The diagnosis of allergic rhinitis rests on your clinical story: what you feel, when in the year, and where you are at the time. A skin prick test or serum specific IgE is then used to support that story (PMID 33273461).

That story is not a formality. Symptoms that return in the same weeks every year, worsen outdoors and settle indoors, point towards pollen more strongly than any number does. Thuisarts describes the same pattern in plain language, and your GP starts there too.

So the order is: story first, test second.

When I searched for hay fever tests myself, six of the top ten results were symptom quizzes. Not one explained what the confirmatory test afterwards actually measures. That is where this article starts.

What does a hay fever test in your blood actually measure?

A hay fever blood test measures specific IgE: the antibodies your immune system makes against one particular allergen. There is no single hay fever number. You get a value per allergen, in kU/l, so separately for grass pollen, birch pollen and mugwort pollen.

That distinction is practical. Birch pollen runs roughly through April and May, grass pollen from mid-May into July, mugwort later in the summer. Once you know which pollen hits you, you also roughly know when your season starts.

Alongside pollen, some airborne allergens are present all year: house dust mite, cat, dog and moulds. Symptoms that are as fierce in January as in June fit those better. A house dust mite allergy test works on exactly the same principle: specific IgE against that one allergen.

The inhalation allergy panel covers the common Dutch inhalation allergens in one go, pollen and year-round allergens side by side.

Total IgE is something else entirely. It adds up all your IgE and says nothing about which allergen causes your symptoms. What a raised value does and does not mean sits in the piece on your IgE level in blood.

Blood test or skin prick test: which is better for you?

The difference that most often decides it: antihistamines generally suppress your skin reaction, so they usually have to be stopped several days before a skin prick test. The doctor performing the test decides exactly how long. Antihistamines do not affect a specific IgE blood test.

So never stop your medication on your own. If a skin prick test is planned, the clinician performing it will tell you what to do and from when.

Do you take a tablet every morning in season, and would rather not, or cannot, interrupt it? Then blood is the logical route.

Beyond that, the two sit close together. In a real-life comparison, skin prick testing and serum specific IgE broadly agreed, with an AUC of roughly 0.84 to 0.94 (PMID 32176225). They are not interchangeable, and both belong next to your clinical history.

An allergy test at the GP therefore usually runs via blood or via a referral to an allergist. A skin prick test is done in the consulting room, with a reaction visible within about fifteen minutes. Blood can be drawn with us without a referral, and the result follows later.

Does a positive result mean you have hay fever?

No, not on its own. These tests denote sensitisation: you make antibodies against an allergen. Atopy and allergy are two different phenomena, so a diagnosis leaning on a test result alone carries a real rate of misdiagnosis (PMID 35386974).

Take two people with the same result: both a specific IgE against grass pollen of 3.5 kU/l. One sneezes through every June, with itching eyes and a running nose that only stops in July. The other notices nothing at all, not even in a freshly mown park.

Same antibody, different life.

Symptoms and sensitisation together make the allergy, never the number alone. That is why we do not let a result stand apart from its context. In the European allergy guidelines the test sits consistently next to the clinical story, not ahead of it (PMID 24909706).

Hay fever or just a cold?

Itch is the most useful distinction. Hay fever often brings itching, watering eyes and a clear, running nose, and those symptoms return around the same weeks each year. A cold builds up, usually runs its course in a week or so, and can come with a fever. This gives you direction, not certainty.

If your symptoms line up neatly with the grass pollen season, a pollen allergy test can settle that doubt.

Hay fever and asthma often travel together. The Longfonds describes that combination of nose and airways, and the ARIA guideline for allergic rhinitis, drawn up with the WHO, is built explicitly around it. Increasing breathlessness or wheezing belongs with a doctor, not with a quiz.

Do you become short of breath, do your lips, tongue or throat swell, or does the reaction look like anaphylaxis? Call 112 or go to the out-of-hours GP service. That is acute care, and not a moment to have blood drawn first.

What do you do with your result?

Knowing which pollen causes your symptoms makes things concrete. You know which months to watch, when a conversation with your GP about treatment makes sense, and what you can adjust at home. Always discuss your result with your GP, who weighs it against your symptoms.

React to birch pollen, and your season sits in spring. If it is grass, it starts around mid-May. If house dust mite is in there too, that explains the symptoms that simply carry on through winter.

With stubborn symptoms a doctor sometimes also looks at your eosinophils, a white blood cell that can be raised in allergy and asthma. What a rise can mean, and above all what it cannot, sits in high eosinophils: allergy, asthma or something else.

To start yourself, pick the allergens that fit your story through building your own blood test. If you suspect food rather than pollen, read what a food allergy test does and does not show.

Are your symptoms vaguer, with gut, skin and head all mixed in, and are you thinking about histamine? Then the story starts at histamine intolerance and what your blood shows. And if you want to learn how to read a result first, understanding blood test results will get you going.

If you land on pollen, the next step is small and concrete. I think that is the honest win here: you finally know what you do and do not react to. Pick specific IgE for the pollens that match your season, get your blood drawn this spring, and take the result to your GP.

References

1. Bousquet J, Anto JM, Bachert C, et al. Allergic rhinitis. Nat Rev Dis Primers. 2020;6(1):95. PMID 33273461.
2. Testera-Montes A, Salas M, Palomares F, et al. Diagnostic Tools in Allergic Rhinitis. Front Allergy. 2021;2:721851. PMID 35386974.
3. Bignardi D, Comite P, Mori I, et al. Allergen-specific IgE: comparison between skin prick test and serum assay in real life. Allergol Select. 2019;3(1):9-14. PMID 32176225.
4. Muraro A, Werfel T, Hoffmann-Sommergruber K, et al. EAACI food allergy and anaphylaxis guidelines: diagnosis and management of food allergy. Allergy. 2014;69(8):1008-1025. PMID 24909706.
5. Longfonds and Thuisarts. Patient information on hay fever, allergy and the airways. Available via longfonds.nl and thuisarts.nl.

Every blood test result at Vitalcheck includes a professional assessment by a BIG-registered doctor. A blood value is not a diagnosis: always discuss treatment decisions with your GP.