Hi

Eosinophilia is defined as an increase in eosinophils, different countries and labs have slightly varying values for their cut off point but in general most will state that a value above 450 is high (some persons may actually use 600 as a reference point).
Normally eosinophils defend the body against parasites, allergies, tissue inflammation.

The medications that your son has been prescribed , the hetrazan-an antiparasitic drug, montair- leukotriene antagonist which treats allergies and is also used in asthma, asthalin-used in asthma as a reliever not preventer medication, indicate that your doctor believes that the increase is related to a parasitic infection or/and his allergies.

The causes are:
(1)allergic disorders such as asthma, hay fever, drug allergies, allergic skin diseases
(2) parasitic infections
(3) some forms of cancer ( the ESR would likely be higher in this case)
(4)some autoimmune diseases (these are conditions where the body is almost fighting itself- in most of these conditions the ESR would be high)
(5)cause can be unknown
(5) toxins

Normally diagnosis is made by blood tests which were done in your son's case ( the platelets are only mildly elevated, this elevation is not at a significant level, the ESR is a non specific marker of inflammation or infection in the body and it is also elevated). If the cause is thought to be obvious (allergies) then futher testing may not be done.
In some persons additional tests such as liver or kidney blood tests, spinal tap (to check for certain worm infestations may be done).Other tests for infection would be stool samples for parasites and ova (parasite eggs)
Some persons with allergic symptoms may have a nasal smear done to check for eosinophilia and the smear may be stained to check for bacteria.

If it is not thought to be a reaction to a allergen, medication,asthma or parasite then analysis of the bone marrow may be necessary.

Treatment depends on the cause.

I hope this helps, feel free to ask any questions

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