Food Allergy Serology

Serologic tests in vitro are easily performed, but some are made with a radioimmunoassay method which complicates somewhat the test and increases costs.

Eosinophil count
In order to make the eosinophil count should be done before a differential diagnosis: infection (due to high number of neutrophils), with congenital anomalies of the turbinate bones, with the irritation irritants, and other etiologies of non-allergic.

Although the number of eosinophils differential count can be achieved as compared to the total number of leukocytes, are used to count themselves more sophisticated methods that color specifically eosinophils (Tannen Pilot or solutions). The total number of eosinophils per mm 3 range from 0 to 450 in adults, in children from 50 to 700 and from 20 to 850 in the newborn.

Total dose of IgE
A high level of serum IgE may confirm the suspected diagnosis of an allergic disease. Since, however, there is a degree of overlap between the values ​​of IgE in allergic and in normal subjects, a normal amount of IgE does not exclude a diagnosis of allergies.

Currently IgE are measured with a radioimmunoassay method: the so-called PRIST (Paper Radio Immuno Sorbent Test or tests of radio-immuno-adsorption on paper). This test uses a solid substrate of paper, they are bound IgE antibodies. after appropriate washing, if they are present in the test serum IgE, these are linked by antibodies attached to the disk of paper. Using anti-IgE antibodies labeled with 125I. securing the IgE bound to the disc and then, after a further washing step, the readings of the disk of paper in a counter for gamma emissions.

The radioactivity of the complex will be directly proportional to the concentration of IgE in test serum. In adults the normal values ​​of serum IgE are less than 0.025 mg / dl.

Determination of specific IgE
It is more important than the dosage of total IgE, in fact, it is useful to confirm doubtful cases, and especially to skin tests for evaluation in young children or people with serious skin diseases.

It uses a test called RAST (Radio Allergo Sorbent Test, tests of radio-allergic-absorption) that has some similarities with PRIST. The allergen is covalently linked to a disk of paper and reacts with specific IgE antibody may be present in the test serum. After non-specific IgE were removed by washing, adding anti-IgE antibodies labeled with 125I, which bind to the complex hard-allergen-IgE. It reads at this point the radioactivity in a gamma counter for broadcasters. This will be proportional to the amount of specific IgE present.

The RAST is less sensitive but more specific than the skin test, and now the new laboratory techniques such as the CAP FEIA or UniCAP Sistem, have high sensitivity and ease of use.

House rapid methods
Point-of-care tests recently have proven practical methods for their self study at home (point of care testing), among them in the field of allergy merits signaling equipment of a Swedish Company: ImmunoCAP Rapid (ICR). This apparecchietto similar to a blood glucose meter for home blood glucose analysis, analyzing a drop of peripheral blood and is useful for the diagnosis of the first level: asthma, eczema and rhinitis. Among the food allergens tested include: eggs, milk, along with other common food allergens.

The reproducibility of the data is good, with a false positive rate of 1%. The tool is therefore useful for a first outpatient diagnosis of the most common allergies, especially in the respiratory tract.

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