In Vitro Allergy Testing
Total serum IgE testing in patients with allergic disease has no established clinical role. Substantial proportions of individuals with IgE-mediated allergic disease have normal serum IgE levels, and many nonallergic diseases are associated with elevated serum IgE. Measurement of serum IgE may be indicated in adults with conditions such as suspected allergic bronchopulmonary aspergillosis and hyper- IgE syndromes (dermatitis and recurrent pyogenic infections), certain stages of HIV infection, IgE myeloma, drug-induced interstitial nephritis, graft-versus-host disease, several parasitic diseases and specific immune deficiency diseases. In children, serum concentrations of IgE increase slowly with development, with highest levels typically found in late adolescence. High concentrations of serum IgE measured in the first year of life have been shown to correlate with future development of atopic disease. However, in clinical situations when presenting signs of allergic disease are evident, total IgE levels do not provide additional diagnostic information. Furthermore, normal IgE levels do not exclude the diagnosis of allergic disease in infants or children.
Total serum IgG, IgA and IgM testing is not typically clinically useful, since their levels are not altered by allergic diseases. Based on a review of the literature, the role of routine quantitative measurement of serum IgG, IgA and IgM in the diagnosis and management of allergic disease has not been established.
Serum IgG antibodies are not involved in the pathogenesis of atopic disease. Although it has been suggested that IgG antibodies may be responsible for delayed symptoms or vague intolerance to foods, there is no evidence available that validates this contention. RAST and similar technologies are capable of detecting minute quantities of such antibodies, and it is known that low-level IgG antibodies to foods circulate normally but have no known pathogenic significance. The measurement of specific IgG antibodies is of no diagnostic value in the management of patients with atopic (allergic) disease. There is insufficient evidence in the published, peer-reviewed scientific literature to support the use of specific IgG antibody testing by RAST or ELISA in the diagnosis or treatment of allergic disease without suspected immunodeficiency.
The cytotoxic test, also known as the “leukocytotoxic test” or Bryan’s Test, has been proposed for food allergies but has no scientific support as a procedure for the diagnosis of food allergies or inhalant allergies. The rationale for this test is based on a claim that morphological changes in peripheral-blood leukocytes in contact with allergens in vitro indicate that the patient is allergic to the particular allergen. There is insufficient evidence in the published, peer-reviewed scientific literature to support the use of this testing in the diagnosis or management of allergic disease. The role of this testing in the diagnosis or management of allergic disease has not been established.
Lymphocyte subset counts may be useful in the diagnosis of lymphocyte cellular immunodeficiencies and lymphocytic leukemias. Quantifying lymphocyte subsets, however, has not been proven to be of any value in the diagnosis or management of allergic disease.
Lymphocyte function assays may be appropriate in the diagnosis of some immunodeficiency diseases; however, they are not abnormal in allergic diseases. The use of this testing in the diagnosis or management of allergic disease is unproven.
Cytokine and cytokine receptor assays have not been shown to be useful in the diagnosis or management of any allergic disease and are therefore considered unproven.
The food immune complex assay (FICA) is based on the solid-phase radioimmunoassay methodology. It has not been shown in well-designed clinical trials that any well-defined clinical disease involves pathogenic circulating immune complexes to foods. Furthermore, it has not been shown that the assay for such complexes is diagnostic of any disease. The clinical value of food immune complex assays in the diagnosis and management of allergic disease has not been established. The technique is therefore considered unproven.
Leukocyte histamine release testing is an in vitro test that evaluates the presence of specific IgE antibodies. The test has been proposed for the diagnosis of various allergic conditions, including atopic disorders and stinging insect allergies. Leukocyte histamine release testing detects the release of histamine from basophils in a sample of whole blood exposed to allergens in vitro. It is a cumbersome test typically conducted in research laboratories, and has not been studied fully for its predictive value in determining specificity and sensitivity. Its role in the diagnosis and management of allergic disease outside of the investigative setting has not been established.
Body chemical analysis is typically seen in the diagnosis of a condition known as “idiopathic environmental intolerances” (IEIs) or “multiple food and chemical sensitivities.” Samples of whole blood, serum, erythrocytes, urine, fat and hair are tested for the presence of environmental chemicals. The most common chemicals measured are organic solvents, other hydrocarbons, pesticides and metals. Some proponents of this testing also recommend measurements of the quantity of vitamins, minerals and amino acids in blood and urine in a search for “environmental sensitivities.” The concept of multiple food and chemical sensitivities manifested by numerous symptoms in the absence of objective physical findings lacks scientific foundation. There is no evidence to suggest that these patients suffer from an immunological abnormality. The existence of such an illness is based on anecdotal reports with no verification using well-designed clinical trials. There is no scientific evidence to support the value of diagnostic testing associated with IEIs or multiple food and chemical sensitivities, including body chemical analysis. Body chemical analysis is therefore considered unproven.
Antigen leukocyte cellular antibody testing (ALCAT) is an automated method of testing for food allergies that is purported to identify food sensitivity by using a modified Coulter counter linked to a computer program to measure the change in white blood cells incubated with purified food and mold extract. There is insufficient evidence in the published peer-reviewed scientific literature to support the use of this testing in the diagnosis or management of allergic disease.