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Discussion on Blood Testing For Allergies (!!??)

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Nancy Brown
Posted on Monday, Jan 24, 2000 - 9:24 pm:   Edit PostPrint Post

Hello Dr.O:
In a previous post, I explained how our veterinary diagnosis allergies from blood test.
Your answer was 'most of the time I find folks have misunderstood the veterinary's meaning ..'
ref: head pressing/Extreme Machine.
While dropping in a blood sample at my vets today, I asked, how do you diagnose a horse with
allergies. She indicated, (using the hematology results of my filly as an example.) The results of Grans (2.8 - 8.0) and L/M (2.1 - 7.0)'should
be' 55%Grans 45%L/M. If the Grans is in excess of 60% - the horse is diagnosed and treated for
allergies.
You explained that Machine's blood work results:(71%Grans / 29%L/M) is a normal leukogram, not ruling allergies out. What I understand my vet saying without any uncertainty is, anything OVER 60% IS allergies. If this is a normal leukogram what is misunderstood is; why recommend treatment of steroids, ventipulmin, and/or various bronchial puffers when allergies is neither proven or ruled out??
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Robert N. Oglesby DVM
Posted on Tuesday, Jan 25, 2000 - 8:34 am:   Edit PostPrint Post

Hello Nancy,
I know of no research, printed information nor does any experience of mine suggest a granulocyte count of 60% or above is diagnostic of a allergy. I do not know any single healthy horse that will have a 55/45% mixture regularly, these numbers are changing minute by minute. I do not know of any pathologist or books on pathology printed in the last 20 years that draw a clinical significance between 55% and 60% neutrophils for any disease state.

Though 55% falls within a normal range that is all it is: a range of values of normal horses usually taken to 1 standard deviation. Is short that means 5% of the normal horses will fall out of the normal range of 33 to 73%.

We publish these figures for adult horses for WBC Diff. Absolute count/Ál (% of total)
stabs rare (0)
segs 1350-8250 (33-73)
lymphs 820-7350 (20-65)
monos 40-700 (1-6)
eos 40-450 (1-4)
basos 40-80 (1-2)
These were taken from a standard reference book on equine lab values but agree very closely to my own labs normals. I checked against a second reference this morning and we all agree: these represent normal values. Despite the range downward to 33% the big majority of horses I check fall in the 50 to 65% range for neutrophils.

What really perplexes me is that there are so many other causes for a rise in neutrophils and no indication that I know of for the allergy interpretation. In Laboratory Profile of Equine Disease (Mosby 1997) these are the reasons listed for an increase in neutrophils:
Stress
Exercise
Excitement
Steroid Administration
Acute bacterial infection that the body is controlling
Cancer
Surgery
I guess you could say, "if he has a allergy he is under stress", but this is a long way from interpreting a normal neutrophil value as indicative of an allergic disease state.

The diagnosis of allergy in horses is based on finding inflammation that is consistent with the known mechanisms of allergic response that cannot be explained by the other causes of inflammation. With the exception of a few well defined and easily recognized entities (anaphylaxis, COPD come to mind), this diagnosis is almost always tentative with no easy way to prove it 100%. Response to appropriate therapy for allergic response, reoccurrence when such treatment is discontinued or a seasonal reoccurrence are highly suggestive of allergy. If there was a question as to whether infection were present I would draw blood but would personally make no clinical distinction for allergy or bacterial infection by a 5% difference in counts within a normal range. A high eosinophil count (above 450 absolute count) would support but not diagnose allergies or parasitism. And that reminds me of one more important point, while percentages can give useful information as the relative number can change in certain states, generally it is the absolute number that needs the closest inspection: 55% of an abnormal count may or may not represent a abnormal number of neutrophils.

I hope this helps.
DrO
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