Evaluation of commercial skin prick test solutions for selected occupational allergens

BACKGROUND

Skin prick testing (SPT) is an important step in the diagnosis of IgE-mediated occupational allergic diseases. The outcome of SPT is related to the quality of allergen extracts. Thus, the aim of the study was to assess different commercially available SPT solutions for selected occupational allergens.

METHODS

SPT was performed in 116 bakers, 47 farmers and 33 subjects exposed to natural rubber latex (NRL), all with work-related allergic symptoms. The SPT solutions from different manufacturers (n = 3-5) for wheat flour, rye flour, soy, cow hair/dander, storage mites (Tyrophagus putrescentiae, Lepidoglyphus destructor, Acarus siro) and NRL were analysed with respect to their protein and antigen contents. SPT was carried out in 16 allergy centres in six European countries using standardized procedures. Specific IgE values were used as the gold standard to calculate the sensitivity and specificity of SPT solutions. The optimal cut-point for each SPT solution was determined by Youden Index.

RESULTS

Protein and antigen contents and patterns of the SPT solutions varied remarkably depending on the manufacturer. While SPT solutions for wheat flour and soy reached overall low sensitivities, sensitivities of other tested SPT solutions depended on the manufacturer. As a rule, solutions with higher protein and antigen content showed higher sensitivities and test efficiencies.

CONCLUSIONS

There is a wide variability of SPT solutions for occupational allergens, and the sensitivity of several solutions is low. Thus, improvement and standardization of SPT solutions for occupational allergens is essential.

[Skin tests for diagnostics of allergic immediate-type reactions. Guideline of the German Society for Allergology and Clinical Immunology]

Skin tests in patients with IgE-mediated immediate type allergy are performed with the intention to establish a contact between allergens and skin mast cells. The latter carry specific IgE antibodies on their surface. If mast cells get activated, mediators (mainly histamine) are released which induce a visible skin reaction (wheal and erythema).[nl]Skin tests are indicated, if an immediate type allergic disease is suspected. Systemic anaphylactic reactions at skin testing are very rare. However, it is necessary to take them into account and to provide emergency treatment. Relative contraindications comprise skin diseases in the test area, poor general condition and insufficiently treated severe asthma. If tests are used, which have a higher risk for a systemic anaphylactic reaction, pregnancy or beta-blocker therapy, are further contraindications.[nl]Skin test application does not depend on patient age. However, in pre-school age tests are reluctantly performed. It is essential to consider the half-life of drugs which may interfere with the test result, and which have to be discontinued early enough before testing. After anaphylactic reactions there may be a refractory period. Therefore, tests should not be done within the first week after such reactions. Skin prick tests are the procedures of first choice, intradermal tests are more sensitive than prick tests. Skin tests are performed at the flexor side of the forearm. As intradermal tests are more inconvenient, testing can be also done at a less susceptible site of the body (upper back).[nl]It is recommended to use standardized test extracts. However, if standardised extracts are not available or do not yield suitable test results, one may switch to other preparations. If the patient shows a positive reaction to a non-standardized substance, control tests should be performed in healthy subjects in order to exclude an unspecific reaction.[nl]The reaction is read after 15 to 20 min. Skin tests are regarded positive if the mean wheal diameter is ≥ 3 mm at the prick test, and ≥ 5 mm at the intradermal test.[nl]Skin test results may be negative although patients are allergic. If a skin test is positive, one will have to distinguish reactions, which are clinically relevant, from those, which are not. History and/or challenge tests help to clarify the relevance of a sensitization. Usually, a clinically irrelevant sensitization does not lead to practical consequences.

Prediction of challenge test results by flour-specific IgE and skin prick test in symptomatic bakers

BACKGROUND

Wheat and rye flours are among the most important allergens causing occupational asthma. Usually, the diagnosis of baker's asthma is based on inhalation challenge tests with flours.

AIMS OF THE STUDY

To evaluate the relevance of flour-specific serum immunoglobulin E (IgE) and skin prick test (SPT) in the diagnosis of baker's asthma and to define flour-specific IgE concentrations and wheal sizes that allow a prediction of the outcome of challenge testing.

METHODS

Bronchial and nasal challenge tests with wheat (rye) flour were performed in 71 (95) symptomatic bakers. Determinations of flour-specific IgE as well as SPTs were performed in all subjects. Analyses included the calculation of sensitivity, specificity, positive (PPV) and negative predictive values (NPV) at different IgE concentrations and different wheal sizes, and receiver-operating characteristics (ROC) plots with the challenge result as gold standard.

RESULTS

Thirty-seven bakers were positive in the challenge with wheat flour, while 63 were positive with rye flour. Depending on the flour-specific IgE concentrations (wheal size), PPV was 74-100% (74-100%) for wheat and 82-100% (91-100%) for rye flour, respectively. The minimal cut-off values with a PPV of 100% were 2.32 kU/l (5.0 mm) for wheat flour and 9.64 kU/l (4.5 mm) for rye flour. The shapes of the ROC plots were similar for wheat and rye flour.

CONCLUSION

High concentrations of flour-specific IgE and clear SPT results in symptomatic bakers are good predictors for a positive challenge test. Challenge tests with flours may be avoided in strongly sensitized bakers.

Sensitization to different mite species in German farmers: clinical aspects

Various mite species referred to collectively as house dust and storage mites are recognized worldwide as a cause of allergic airway disease. Our study aimed to investigate the frequency of sensitization and potential importance of mite species in farmers using a broad mite spectrum. A total of 86 German farmers with rhinitis and/or asthma were studied by skin prick testing and/or enzyme allergosorbent test (EAST) with the following mites: Blomia tjibodas, Blomia tropicalis, Blomia kulagini, Glycyphagus domesticus, Thyreophagus entomophagus, Euroglyphus maynei, Chortoglyphus arcuatus, Dermatophagoides pteronyssinus, Dermatophagoides farinae, Acarus siro, Lepidoglyphus destructor, Tyrophagus putrescentiae, Acarus farris and Cheyletus eruditus. Sensitization to at least one mite species was detected in 51 patients (59%) by skin prick testing, and in 31 patients (36%) by EAST. The most frequent sensitizations determined by skin tests were found for the three Blomia species, E. maynei and G. domesticus. Twelve patients (14%) gave a positive EAST with the predator mite C. eruditus. A total of 22 patients gave positive EAST results with the Dermatophagoides species. We were able to document sensitization to C. arcuatus, E. maynei and T. entomophagus for the first time in Germany. A considerable proportion of the German farmers tested were sensitized to storage mites. The allergological potential of various mite species has been recognized, some for the first time. It was concluded that B. tjibodas, G. domesticus, C. arcuatus and C. eruditus in particular should be included in an allergy diagnosis. Further investigations into the clinical relevance of the sensitizations and possible cross-reactivity between the mite species are necessary.

[Sensitization in budgerigar owners]

In a prospective study 258 adults were investigated for sensitisation against bird antigens (budgerigar, canary, pigeon) using intracutaneous test. 18 of 78 budgerigar keepers were sensitised against budgerigar feathers. 30 (38%) showed a positive skin reaction at least with one of the three extracts tested. In none bird exposed persons a sensitisation was found in 18/96 (19%) against budgerigar and in 24/96 (25%) against at least one of the three allergen extracts. Late reactions occurred in 5/70 (7%) budgerigar keepers, 4/5 with pigeon feathers. The frequency of sensitisation against budgerigar antigens increased to 48% of bird keepers (24/50) if the birds could fly in their homes instead of being caged always (4/22, 18%). Three of the 78 budgerigar keepers (4%) had a positive nasal provocation with feathers extract, they were skin positive against all three bird antigens tested.

Mite fauna of German farms

Storage mites are important sources of airborne allergens, especially on farms. A mite survey was conducted in the working environments of 121 farms in five regions of Germany. Of 859 samples, 743 (86.4%) contained mites, representing 547,857 astigmatic mites in 723 g of dust and 34,501 prostigmatic mites in 469 g of dust. Dust samples from nine sites of each farm were collected and analyzed. Ninety-three percent of all mites belonged to the order Astigmata (storage- and house-dust-mite species); 35 Astigmata and 14 Prostigmata mite species were identified. According to the abundance and steadiness of the important astigmatic mite species, the following order was found: Lepidoglyphus destructor > Glycyphagus domesticus > Acarus siro > Tyrophagus longior > Blomia tjibodas > Chortoglyphus arcuatus > Thyreophagus entomophagus > Tyrophagus putrescentiae > Euroglyphus longior > Tyrophagus palmarum > Acarus farris > Acarus immobilis > Gohieria fusca. Blomia tjibodas was described for the first time as an abundant species of farms in Germany.

[Encasing evaluation: studies of dust retention and water permeability]

The use of allergenproof mattress casings for those allergic to house-dust mite is a vital component of therapeutic concepts concerning the avoidance of allergens. Encasings of different materials are available from a variety of manufacturers on the German market. The goal of this study was to investigate different encasing materials to test for their impermeability to dust and permeability to water vapour ("breathability"). Material samples from nine different manufacturers as well as one additional samples were tested by two independent institutes. The samples were coded with serial numbers and the product names and manufacturers were unknown to the testers. The degree to which particles could penetrate the materials (as a measure of dust penetration) was tested in two series of experiments using the naturally available ambient air and fine coaldust. A thermo-regulation model ("skin model") was used to test the materials for water vapour permeability. The results of three of the nine samples tested for particle penetration have to be considered unsatisfactory due to the number and size of the particles allowed to enter. Overall an additional synthetic layer appears to improve the materials capacity to prevent dust penetration. The water vapour permeability of three of the nine samples of encasing material must be classified as unsatisfactory with the consequence of possible sleep disturbance. From an allergological point of view, minimal particle penetration is an essential criteria. On the other hand, low water vapour transport properties can diminish the patients willingness to comply. The present study cannot be substituted for a clinical study of effectiveness but nonetheless reveals, in some cases, considerable differences in the physical properties of the various materials. It would be desirable for the individual product packaging to feature a declaration of the relevant test data, thus providing decision-making for those buying or prescribing.

[Clinical experiences with cefixime in the treatment of bacterial infections of the lower respiratory tract]

In a prospective, open clinical trial 21 patients suffering from lower respiratory tract infections were treated with the new oral cephalosporin cefixime. The antibiotic was given at a dosage of 200 mg b. i. d. for seven to eleven days. Seventeen of 18 evaluable patients were cured or distinctly improved at the end of therapy as well as two days after the end of treatment. Clinical results correlated well with the results of the lung function tests, especially with the significant decrease of resistance. At the end of therapy all initially isolated pathogens were eradicated. The tolerability of cefixime was good, only in two patients treated mild and transient side effects were noticed (1 x diarrhea, 1 x epigastric pain).