Eosinophils

Some laboratories use an upper limit of 0.5; the count is lowest in the morning and higher at night; use the range your lab printed.

Eosinophils are white blood cells involved in allergic reactions and in the response to parasites. In asthma and some other airway conditions the blood eosinophil count is used as a marker of the type of inflammation present. This is the absolute number in a given volume of blood.

It is part of the full blood count differential. Doctors look at it in asthma, eczema, hay fever and other allergic conditions, after travel, and when someone has an unexplained rash, cough or raised count on a routine test. Respiratory clinics often follow it over time.

• Asthma, eczema, hay fever and other allergic conditions
• Reactions to medicines
• Parasitic infections, particularly worms picked up abroad
• Some skin conditions
• Some autoimmune and inflammatory conditions
• Some blood conditions
• Adrenal gland underactivity

• Steroid medicines, including inhaled and tablet steroids
• Acute bacterial infection
• Stress and the hours after surgery
• Cushing's syndrome, where the body makes too much steroid hormone

• A morning sample reads lower than an evening one
• Steroid tablets or a recent steroid course lower it as an expected effect
• Hay fever season raises it in people with pollen allergy
• Counts near zero are common in the general population and are not of any importance

No fasting needed. Time of day and recent steroid use matter; a trend across several samples is more useful than one value.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.