Eosinophils

Also written as: absolute eosinophil count, eos

White blood cells central to allergic reactions and defense against parasites.

What it measures

The number of eosinophils in the blood. Eosinophils are white blood cells packed with granules that play a central role in allergic responses and in defending the body against parasites.

Why a doctor orders it

It comes with the white cell differential on a complete blood count. Clinicians look at it when evaluating allergies, asthma, unexplained rashes, suspected reactions to medications, or possible parasitic infection.

What is generally associated with a higher result

Broadly associated with allergic conditions such as hay fever, asthma, and eczema, with reactions to medications, and with parasitic infections. Persistent, marked elevations are what lead to a broader evaluation rather than a single mildly raised value.

What is generally associated with a lower result

Broadly associated with acute stress, acute infection, and corticosteroid medicines. Low counts are generally not pursued.

Everyday things that move this number

Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:

Active seasonal allergies or an eczema flare at the time of the draw
Corticosteroid medicines, which lower the count sharply
Time of day - counts naturally swing over 24 hours
A recently started or changed medication

Questions to take to your appointment

Could my allergies, asthma, or a skin condition account for this?
Could any of my current medicines be playing a role, in either direction?
Is this at a level where further evaluation is usually considered, or in watch-and-see territory?

Build a printable questionnaire with your own results →

Where to read more

MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .

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