Allergen-coated lancets (Phazet) for skin prick testing in children

With a new allergen-coated lancet (Phazet), skin prick tests can be made directly on the skin without separate use of liquid extract (the Phazet dry method), and reactions are recorded as for the ordinary method with liquid allergen extract (Pharmalgen) (the Pharmalgen wet method). 100 children were tested in parallel with the two methods. As a double control each Phazet was used twice (Phazet 1 and 2) in each child, who was tested with nine standard allergens. Good agreement was found between the results obtained with the two methods and also between Phazet 1 and Phazet 2. No general reactions were shown in relation to the numerous skin prick tests with allergen extract of a strength up to 100,000 BU/ml. 66% of the children preferred the Phazet while 22% had no preference.     

Allergy screening including a comparison of prick test results with allergen-coated lancets (Phazet®) and liquid extracts

During an allergy screening of families with a history of allergy in one or more subjects, skin prick tests (SPT) were performed in duplicate in 314 adults. The tests were performed with a new type of lancet with a 0.9 mm long point, loaded either with allergen (Phazet) or used together with standardized extracts (10,000 and 100,000 BU/ml). Wheals obtained with both methods were compared, and related to total IgE concentrations and history. A wheal area of 3 and 7 mm2 was used as cut-off limit. Results with Phazet were close to those with Pharmalgen 100,000 BU/ml. With both methods precision was good for allergens, but less for Phazet histamine than for the corresponding wet test. SPT results obtained with Phazet and 100,000 BU/ml correlated better with history than the results with 10,000 BU/ml. Using a wheal size of 7 mm2 as cut-off limit the efficiency for five tested allergens was 91%. "False positive" tests, possibly indicating an unobserved or latent type of allergy, were found more often with higher serum IgE concentrations. The safety of SPT was confirmed and Phazet was well accepted by nurses and tested subjects.     

A study of skin test with regard to age differences and agreement with positive results from the RAST and ELISA methods]

Skin tests of the scratch type were performed on 132 asthmatic patients with 28 allergens. The threshold titers of skin test, RAST and ELISA of house dust, HD mites, Japanese cedar pollen, ragweed pollen and orchard grass pollen were included. The main skin-positive allergens among the patients were as follows: house dust, HD mites, Japanese cedar pollen, orchard grass pollen, timothy grass pollen and ragweed pollen. There are age differences on skin-positive rates among 4 age groups of the patients; 90% of the patients under 40 years old groups reacted positively to any of 28 allergens, while half number of the patients groups over 40 years old reacted positively to the allergens. According to the quantitative analysis between threshold titers of skin test and RAST titers using house dust and HD mites allergens, specific IgE production shall be decreased in the patients over 40 years old. Using 5 main allergens above mentioned, the agreements of positive responses between three methods were compared. RAST positive responses correlated well with the skin test results, while ELISA positive responses correlated rather poorly with the skin test results. However, correlation between RAST and ELISA results was relatively good. The correlation of positive responses to house dust and HD mites by the three methods was very good, but there were some cases where positive responses were obtained by only one of the methods.     

Evaluation of a capsulated hydrophilic carrier polymer (the ImmunoCAP) for measurement of specific IgE antibodies

The Pharmacia CAP System is a new assay for serum specific IgE, utilising a solid phase capable of binding more antigen than conventional systems. The CAP System has been evaluated in 69 consecutive patients referred to one allergy clinic in relation to skin prick test (SPT), radioallergosorbent test (Phadebas RAST) and specific allergy diagnosis for five inhalant allergens, D.pteronyssinus, timothy grass pollen, cat epithelium/dander, Cladosporium and Alternaria. Good correlation was obtained between RAST and CAP for all allergens, e.g. r = 0.974 for D.pteronyssinus and r = 0.964 for grass pollen. When sensitivity and specificity were examined for both CAP and RAST versus SPT, CAP was usually found to be of greater sensitivity than RAST, and of similar or slightly lower specificity. SPT gave more positive reactions than either in vitro test, but CAP gave more positives than RAST. Twenty-two of 336 (6.6%) tests were CAP positive/RAST negative, whereas a negative CAP with a positive RAST occurred in only 2/336 (0.6%) tests. Of patients with any test (SPT or RAST or CAP) for specific IgE positive, up to 20-30% did not have clinical allergy, confirming the importance of the history in interpreting these tests. Our results suggest that, for the allergens tested, the Pharmacia CAP System is more sensitive than the RAST, identifying more positive tests and approximating more closely to the SPT. It offers the additional advantages of speed and efficiency.     

The diagnostic value of a new whole blood histamine release test using paper disc-coupled antigens--results compared with intracutaneous test, RAST, and eye test]

We have developed a novel histamine release test (HR) using whole blood and antigen-coupled RAST paper discs, for the screening of allergens rather in a short time with a small amount of blood. Histamine was determined by a RIA kit. In order to evaluate the diagnostic value, the results of the test were compared with those of RAST, intracutaneous tests, and eye tests in 45 allergic patients. HR correlates better with RAST than intracutaneous test in almost all antigens. The closest positive correlation with the other tests was seen in mite allergen, followed by pollen, foods and mould spores in that order. When the HR was positive for house dust, 100% of the patients were also positive for the eye test, which is reported to closely correlate with bronchial provocation tests. HR seemed to be a useful test not only for the screening but also for the determination of pathogenic allergens.     

Basophil histamine release in the diagnosis of house dust mite and dander allergy of asthmatic children

The aim of the study is to compare the glass fibre-based basophil histamine release test with skin test (Phazet), RAST (Phadebas) and bronchial provocation test in children with allergic asthma. The study comprised 68 selected children with a case history of extrinsic allergic asthma to danders (cat and dog) and house-dust mite. Skin prick test, RAST, and histamine release were performed in all children and the bronchial provocation test was used as a reference of "true allergic asthma". A total of 81 allergen bronchial challenges were performed and 44 children experienced 49 positive provocations. In 2.9% (2/68) of the children histamine release could not be performed due to technical difficulties (low histamine release with anti-IgE). Concordances in the range 76-87% were observed with no significant difference between the tests. The highest concordance (87%) was found between histamine release and bronchial provocation test followed by skin prick test vs bronchial provocation (84%) and RAST vs bronchial provocation (80%). The sensitivity and specificity were calculated for each test. All tests showed sensitivities in the range 90-94% and no significant difference between them was observed. The specificity of histamine release, skin prick test, and RAST was 0.78, 0.69, and 0.63, respectively. The specificity of histamine release was better than RAST demonstrated by 95% confidence intervals. In conclusion, it was found that the histamine release test is a convenient diagnostic method and the study indicates a diagnostic value comparable to the common diagnostic methods in clinical allergy.     

Sensitivity to tomato and peanut allergens in children monosensitized to grass pollen

Possible associations between allergy to grass pollen and positive skin tests to food allergens were studied in 102 children monosensitized (as to inhalant allergens) to grass pollen, and in 117 children monosensitized (as to inhalant allergens) to Dermatophagoides. Thirty-two foods were tested by an epicutaneous method. Positive skin tests to food allergens were more frequent in children with allergy to grass pollen (59.8%) than in children with allergy to Dermatophagoides (9.4%). A considerably high frequency of positive reactions to tomato (39.2%), peanut (22,5%), green pea (13.7%), and wheat (11.7%) was observed in children with allergy to grass pollen. Positive skin tests to peanut closely correlated with positive RAST results and nasal provocation tests, whereas in children with skin test positivity to tomato a close correlation with nasal provocation tests but a 45% correlation with a positive RAST result were observed. RAST inhibition experiments were carried out, and the results may suggest the presence of cross-reacting IgE to grass pollen, tomato, and peanut antigens. Clinical implications of these findings are discussed in the light of histories of food hypersensitivity, urticaria-angioedema, and atopic dermatitis in children with allergy to grass pollen.     

Comparison of skin tests and RAST in the diagnosis of atopic hypersensitivity.

Prick, intracutaneous tests and the radioallergosorbent test (RAST) were performed with 12 common allergens in 50 consecutive patients who required skin testing during an allergy investigation. Results of prick test and RAST showed agreement in 82.7% of tests but positive prick tests were much commoner than positive RAST tests. When intracutaneous tests were required to obtain a positive skin test, agreement between skin test and RAST fell to 66.5%.     

Influence of IgG antibody and glycopeptide allergens on the correlation between the radioallergosorbent test (RAST) and skin testing or bronchial challenge with alternaria.

The radioallergosorbent test (RAST) for alternaria was compared to skin tests and bronchial challenges in children suffering from chronic intractable asthma. In contrast to when such children were tested with a timothy grass pollen extract, the bronchial challenge and skin test results against alternaria did not correlate significantly. When alternaria allergens were coupled to cyanogen bromide-activated microcrystalline cellulose, the RAST correlated with the results of skin testing but not bronchial challenge. It was demonstrated by column immunabsorption that some allergic sera contained sufficient IgG antibody against alternaria to competitively inhibit the RAST. When Sepharose 2B was substituted for cellulose as the insoluble support, the inhibition by IgG antibody was largely overcome and then the RAST correlated with both skin test and bronchial challenge results. Glycopeptides contribute significantly to the allergenicity of alternaria, and when these materials were coupled to a Sepharose 2B conjugate by mild oxidation, the RAST correlated with bronchial challenge, but not skin test, results. It was concluded that in this group of steroid-dependent asthmatic children, the correlation of the RAST with the in vivo challenges was strongly influenced by the presence of IgG antibody in the allergic sera and the chemical nature of the mould allergens investigated.     

Discrepancies between the skin test and IgE antibody assays: study of histamine release, complement activation in vitro, and occurrence of allergen-specific IgG

Intracutaneous skin tests (STs) and RAST with the common allergens, grass pollen, house dust mite, and cat dander, were performed on 660 adult patients. In 117 patients (18%), we found 140 discordances (7%) in a total number of 1980 ST and RAST combinations. In agreement with studies in the literature, greater than 80% of the discordances consisted of positive skin reactions without detectable allergen-specific IgE antibodies in serum. The percentages of discordant results were similar for the three allergens. Reproducibility of both the RAST and the ST was evaluated in the discordant group. Repetition of the routine RAST procedure elicited results similar to those in the first test in 81% (105/130). A second ST elicited identical results in 89% (47/53). In addition to the routine IgE antibody assay, sera of patients with a positive ST but without detectable IgE antibodies were tested in two other RAST systems: (1) a RAST with allergen extracts from the same production batch as the ST reagents, and (2) the Pharmacia RAST. In spite of having a clearly positive ST, sera from 68 (80%) of 85 patients remained completely negative in all three RAST systems. Histamine release (HR) in vitro from washed leukocytes was studied in 35 patients with a reproducible positive ST and negative RAST results with serum. Interpretation of this test was possible in 28 patients. In 82% (23/28) of these patients, clearly detectable HR was found with the relevant allergen extract. A role of IgE in the skin reactions and HR tests was confirmed by positive RAST results with IgE that was affinity purified from serum of seven of these patients. Allergen-specific IgG4 antibodies are unlikely to be implicated, since no antibodies against grass pollen and house dust mite were detectable in sera of these patients. Only 18% of the patients with an unexplained skin reaction with cat dander have detectable IgG4 antibodies, but these antibodies were found in a similar frequency in a nonallergic, ST negative control group. Low total IgG responses precluded false negative RAST results caused by competition of IgG antibodies with IgE antibodies. There were no significant differences in the degree of complement activation in vitro by house-dust extracts between healthy control subjects, nonallergic patients, and patients with unexplained skin reactivity. It is concluded that a high proportion of the positive skin reactions with common inhalant allergens, which are not accompanied by a positive RAST, are probably caused by IgE antibodies that are not detectable in serum with any of the RAST procedures.(ABSTRACT TRUNCATED AT 400 WORDS)     

Diagnostic tests in ragweed hay fever. A comparison of direct skin tests, IgE antibody measurements, and basophil histamine release

In 87 patients with both spring and fall hay fever symptoms the radioallergosorbent test (RAST) technique for specific IgE antibodies to ragweed was compared with basophil histamine release and direct intradermal skin testing by the threshold dilution technique. The three techniques gave good agreement except with the leastsensitive patients, some of whom had a positive skin test but undetectable histamine release or IgE antibodies. Twenty-one patients who were highly sensitive to ragweed as measured by all three techniques were followed without specific immunotherapy. There was significant agreement between the level of positivity of all three tests and the symptom index obtained during the ragweed season. In 14 of the 21 patients there was a significant correlation between daily ragweed pollen counts and daily symptom indexes during the season. On the other hand, among the 16 least-sensitive patients (as judged by histamine release) the correlation between daily ragweed pollen counts and symptom indexes was significant in only 3 patients. Other significant allergens could not be identified in the latter group, and the cause of their symptoms is not clearly identified but appears not to be ragweed. The RAST is a quantitative technique that gives diagnostically useful information in ragweed hay fever, although not significantly different from basophil histamine release or carefully performed skin testing. The convenience to the patient may, however, offer a noticeable advantage.     

The radioallergosorbent test (RAST) in the diagnosis of reaginic allergy

Provocation tests, skin tests, and RAST were performed in 156 asthmatic children, using eleven different allergens (moulds, animal danders, and pollens). A total of 305 positive and 676 negative provocation tests were performed. For positive provocations there was an overall agreement with RAST in 61% of the instances, for negative bronchial tests in 94%. The agreement was found to be allergen dependent. By combining RAST and skin tests, it was possible to arrive at a conclusive allergy diagnosis in a higher number of instances than if either skin testing or RAST was used alone, but in a considerable number of instances provocation tests were found to be necessary to secure the allergy diagnosis. The results obtained with RAST in this study were less favourable than those of other studies, probably because of the use of lower quality allergosorbent material.     

Relationship of Allergen-Specific IgE Antibodies, Skin Prick Tests and Allergic Disorders in Unselected Adolescents

The relationship between serum levels of allergen-specific IgE (RAST) and skin prick test reactivity and allergic disorders was evaluated in 137 subjects randomly selected from an adolescent population. All subjects were prick tested with six common allergens, interviewed and physically examined. In addition, serum was collected for RAST analysis with three to six allergens. At least one positive RAST result (score 1-4) was observed in 40% and at least two positive RASTs in 22% of the subjects. Boys experienced more RAST reactions and generally with higher scores than girls. For instance, 26% of boys but only 11% of girls were RAST positive to timothy grass pollen. The correlation between prick test and RAST results was better with pollens than with house dust and animal epithelia. When the test results were discordant, the skin test was usually positive and RAST negative. Many of the small skin reaction (weal diameter 3-4 mm) were accompanied by a negative RAST. Respiratory allergy was closely connected with both positive skin test and RAST reactivity, while atopic dermatitis was less related. In 17% of the adolescents positive skin tests and in 14% positive RASTs occurred in the absence of any allergic symptoms. We conclude that a positive RAST score 3-4 to inhaled allergens is a strong indicator of clinical allergy but low scores 1-2 are frequently found in healthy young people.     

Diagnosis of reaginic allergy with house dust, animal dander and pollen allergens in adult patients. I. A comparison between RAST, skin tests and provocation tests.

RAST analyses were performed with house dust, animal dander and eleven pollen allergens in 410 adult patients with asthma and/or rhinitis and the findings were compared with skin test and provocation test results. The overall correlation between 1,316 provocation tests and RAST was 78% and the correlation between 1,778 skin tests and RAST was 66%. The relationships between RAST and in vivo tests differed considerably from allergen to allergen. No significant differences were found between various age groups. According to the in vivo tests the RAST showed more often positive results in patients with pronounced allergy than in patients with low-grade allergy. Higher RAST classes were most often combined with positive in vivo tests. It is concluded that in cases with RAST classes 2-4, a reasonably well-established allergy diagnosis can be reached without the inclusion of additional in vivo tests. In other cases, however, application of further diagnostic methods is required.     

Diagnostic and therapeutic applications of a modified radioallergosorbent test and comparison with the conventional radioallergosorbent test

A modified radioallergosorbent test (RAST) assay and scoring system (Fadal/Nalebuff RAST) have been purported to increase the diagnostic accuracy and sensitivity of the RAST. In order to assess such claims, we compared this modified RAST with the conventional Phadebas RAST in 40 patients with seasonal allergic rhinitis. Phadebas and modified RAST scores to nine allergens were highly correlated (r = +0.93) and results from either RAST correlated with skin-test titration end points. Clinical sensitivity to test allergens was assessed using nasal provocation titration; positive RAST determinations by both methods were associated with negative provocation tests in fewer than 10% of cases. However, positive provocation tests were noted in over half the patients who had negative Phadebas RAST results; the inclusion of an additional reference point at the lower end of the standard curve may increase the diagnostic accuracy of the test. Non-IgE-containing control preparations produced equivocal results in up to seven of 21 modified RAST assays, but produced negative results in all Phadebas RAST assays. Background binding produced by negative control preparations varied considerably among different allergen discs, indicating that the cutoff point between positivity and negativity may vary from allergen to allergen. The modified RAST was also used to calculate initial immunotherapy doses. Preliminary skin tests at these predicted allergen concentrations produced large wheals (>16 mm) in 15 of 50 trials (30%), and in this situation immunotherapy doses were withheld. The remaining 35 patients tolerated the initial immunotherapy doses without incident. As presently performed, the modified RAST assay does not afford significant diagnostic advantages over the Phadebas RAST; until such a time as standardized allergen extracts are available, potential therapeutic applications of the modified RAST remain speculative.     

Diagnostic value of a glass fibre-based histamine analysis for allergy testing in children

The aim of this study was to compare the diagnostic value of common allergy tests with basophil histamine release in 124 children with symptoms of asthma. The patients were evaluated by case history, skin prick test, RAST-analysis, and basophil histamine release using a glass fibre-based histamine assay to 10 common inhalant allergens. The bronchial provocation test was used as a reference of "true" IgE-mediated asthma. To compare the various diagnostic parameters each absolute test value was classified into a scoring system. The concordance between the tests varied between 85-97%. In general, the best concordance was found between basophil histamine release and RAST. Sensitivity, specificity and predictive values were calculated on the basis of 104 bronchial provocation tests. It was found that histamine release was the best single analysis, followed by RAST and prick testing. The sensitivity of RAST and histamine release was very high (1.00) for pollen and house dust mites. Histamine release showed a predictive value between 0.91 and 1.00 for pollen and house dust mites, thus indicating the possibility of omitting the bronchial provocation test. In the dander group histamine release gave the best sensitivity (0.91), however at the expense of specificity (0.64), whereas RAST and skin prick test gave a specificity of 1.00. In the mould group histamine release also showed the best diagnostic value. The combination of skin testing with histamine release or RAST was of no additional diagnostic help. It is concluded that the glass fibre-based histamine analysis, which makes routine histamine release testing possible, is a reliable diagnostic test in children.     

Comparison of results of skin prick tests (with fresh foods and commercial food extracts) and RAST in 100 patients with oral allergy syndrome

One hundred adult patients with a history of oral allergy syndrome (OAS) after ingestion of fruits and vegetables, 77 patients with hay fever and 13 with skin prick tests and RAST positive to pollens but without seasonal symptoms, and 32 normal nonallergic control subjects, had Phadebas RAST and skin prick tests with commercial extracts (CSPT) and with fresh foods (FFSPT) to assess the reliability of these three tests. Sensitivity was better with FFSPT for carrot, celery, cherry, apple, tomato, orange, and peach; better with CSPT for peanut, pea, and walnut; and better with RAST for hazelnut. Specificity, negative predictive value, and positive predictive value of the three tests were determined for apple, carrot, hazelnut, orange, pea, peanut, and tomato. Specificity in the patient groups ranged between 40% (pea) and 100% (apple) for CSPT, between 61% (peanut) and 87% (carrot) for RAST, and between 42% (carrot) and 93% (peanut) for FFSPT. However, all tests were negative in the control group. Thus, false positive results may result from cross-reactivity with pollen allergens. The diagnostic accuracy of these tests in the population with OAS proved comparable for peanut, carrot, hazelnut, and pea. FFSPT proved more sensitive than CSPT or RAST in confirming a history of OAS to certain alimentary allergens, such as apple, orange, tomato, carrot, cherry, celery, and peach.     

Allergy diagnosis with the radioallergosorbent test: A comparison with the results of skin and provocation tests in an unselected group of children with asthma and hay fever

The radioallergosorbent test (RAST) has been used for in vitro diagnosis of asthma and hay fever in children as an integrated part of the routine procedure for allergy diagnosis. A positive RAST test was combined with a positive prick test in $\text{196}\text{235}$ (80 per cent) tests and with a positive provocation test in $\text{163}\text{182}$ (90 per cent) tests. When the provocation test was positive to dry pollen, the stock solution ($\text{1}\text{10}$ w./v. or 10,000 PNU) of the allergen extract RAST was quite often negative, a fact that explains the lower degree of correlation for a negative RAST test. A comparison between the prick test and the provocation test revealed a high proportion, $\text{54}\text{146}$ (37 per cent), of positive prick tests that could not be confirmed by the provocation test. RAST is a simple, reliable test for IgE antibodies that is very useful for in vitro diagnosis of atopic allergy on a routine basis. RAST is harmless and less traumatic than skin testing and therefore suitable for use even on very small children. The information obtained on the patient's hypersensitivity is more relevant than that from regular skin testing, probably comparable to skin test titration with selected allergens but not quite as good as provocation testing of the shock organ involved. Whenever a provocation test cannot be performed for each suspected allergen, an RAST test, possibly completed with a prick test, is recommended.     

Dissociation of house dust allergies. A comparison between skin tests, inhalation tests, specific IgE and basophil histamine release measurements.

The present study was undertaken to identify the most dominating allergens giving positive reactions both in vivo and in vitro, in patients with house dust (HD) hypersensitivity. Among 655 subjects with positive skin test reactions for HD, 469 (i.e., 71%) had positive reactions for Dermatophagoides pteronyssinus (D.pt.), and 186 (i.e., 28%) had negative reactions for D.pt.; among these 186 patients, 96% reacted to other different allergens, especially to animal epithelia. Challenge tests were performed in 52 patients. In 40 subjects with positive skin tests to HD and D.pt., all gave positive reactions to both tests. Among 12 patients, negative to D.pt. but positive to animal dander, provocation tests confirmed hypersensitivity to animal dander and absence of reaction after inhalation of D.pt. extract. Laboratory studies used specific IgE determinations (RAST Phadebas) and histamine release from human leukocytes. Of 240 HD-hypersensitive patients with serum IgE to HD, 204 also had positive RAST results for D.pt. and 36 for other allergens, there was a high incidence of cat dander (29/36). In a total of 13 dust-allergic people with positive skin tests for HD and D.pt., the relative cell sensitivity for these two extracts was determined from the allergen concentrations, which elicited 50% histamine release. The same biological parameters were determined in a group of 10 patients with positive skin tests to HD and cat dander, and negative skin tests to D.pt., for D.pt., HD, and cat dander extracts. Patients having positive skin tests to HD and D.pt. were also good histamine releasers for these two allergens. On the other hand, we could demonstrate that leukocytes from patients negative to D.pt. were really hypersensitive to cat dander. Our results demonstrate that neither HD skin tests nor HD RAST can characterize the effective allergens responsible for HD hypersensitivity. Identification of the major allergens present in HD, variable in each individual case, could aid toward more specific diagnosis.     

Total IgE influences the relationship between skin test and RAST

Positive correlations were found between total IgE, skin prick test (SPT) and RAST results with tree pollen allergens. The relationship between SPT and RAST was influenced by the level of total IgE. At each level of atopy, defined according to the strength of SPT, patients with high total IgE had higher RAST values than patients with low total IgE.