Po PolskuPublished in: R. Spiewak (Editor): "Pollens and Pollinosis: Current Problems". Institute of Agricultural Medicine, Lublin (Poland) 1995, pages 87-88.
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Recent remarkable progress in the study of atopic diseases has allowed researchers to develop new methods accelerating and facilitating a correct diagnosis, including techniques permitting evaluation of IgE levels. A very brief half-life of IgE in the blood serum accounts for its extremely low average concentration of only 0.03 mg% in healthy adults (the respective IgG concentration is 1250 mg%), which determines the need for highly sensitive and specific testing methods. The time-consuming methods of determination of IgE levels (RIA and EIA) as well as their variants can only be employed in highly specialized diagnostic laboratories. Only the use of Visagnost, an assay recently worked out to facilitate fast titration, permits the researchers to obtain results in less than two hours.
The purpose of this study was to compare specific IgE titrations obtained using Quidel Visagnost and Pharmacia Cap-FEIA techniques for the same allergens.
Fifty patients were evaluated in our Allergy Outpatient's Department Teaching Hospital. They included 23 males and 27 females aged 18-40, with diagnosed upper respiratory tract allergy (grass pollinosis and perennial allergic rhinitis), confirmed by their clinical histories and skin tests. In order to determine specific antibodies were used skin-test positive allergens such as timothy grass, Alternaria tenuis, birch as well as two species of mites (Dermatophagoides pteronyssinus and Dermatophagoides farinae).
Visagnost, a multi allergen dipstick assay derived from ELISA assay, consists in using a plastic dipstick (solid phase) with a control field and test fields containing purified extracts of allergens IgE specific to nine allergens in the inhalatory set and ten allergens in the food set can be determined simultaneously in the serum, plasma or whole blood. The blood must be taken into a tube containig suitable amounts of heparin or disodium versenate (EDTA). Bovine alkaline phosphatase combined with mouse monoclonal antibodies serve as the test-enzyme, while 0.2% buffer solution of 5-bromo-4-chloro-3-indolyl-phosphate is the substrate. Visagnost can be performed in less than 2 hours. The reading consists in visual comparison of colours in test and control fields to colours on a four-degree scale.
Cap-FEIA System is a complete system for in vitro allergy diagnosis which is derived from the ELISA assay. The solid phase is ImmunoCap containing prepared cellulose, covalently bound with a purified allergen extract. The enzyme used is *-galactosidase combined with rabbit monoclonal antibodies and its substrate is 4-methylumbellipheryl-*-D-galactoside. The technique involves also titration of IgE in standard sera which contain fixed concentrations of that antibody: 0.35, 0.7, 3.5, 17.5, 50 and 100 i U/ml. The results of titration aid in drawing a model curve which represents levels of IgE in patients, subsequently assigned to classes 0-6.
The best results have been obtained for timothy grass (90.0% sensitivity, 100.0% specificity and 92.0% agreement). Other allergens demonstrate the range of 88.2-93.3% and 70.0-86.0% for specificity and agreement respectively. Only sensitivity shows a lower range of 60.6-83.3%. A very low concentration of IgE in serum is probably responsible for the weak colours on the dipstick, which renders difficult a correct classification of the results.
Our study of Visagnost and Cap-FEIA has shown an 83.5% agreement of the results as well as a high specificity of Visagnost (average 93.4%), with sensitivity averaging 79.3%. The above leads to the following conclusions:
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