Phadebas RAST Research Articles

Chapter 31: Common in vitro tests for allergy and immunology

Allergen-specific IgE antibody is the most commonly ordered in vitro test in the practice of allergy and is used to diagnose type I hypersensitivity reactions to foods or reactivity to aeroallergens in patients with relative contraindications to skin-prick testing such as dermatographism. The Phadebas radioallergosorbent test (RAST; Pharmacia, Uppsala, Sweden) was the first assay reported for the detection of the allergen-specific IgE antibody. In a RAST, antigen (allergen) is bound to a solid phase, such as a paper disk, and then incubated with human serum. A buffer wash removes unbound serum proteins, and radiolabeled anti-human IgE is added to detect bound IgE, if present. The results are reported in arbitrary units of IgE per milliliter of serum. The term RAST was originally a brand name but it is now often used colloquially (and incorrectly) to describe any in vitro assay for allergen-specific IgE. Total serum IgE can be measured and is helpful in determining atopic presentations such as in allergic bronchopulmonary aspergillosis or in patients with persistent asthma who are candidates for monoclonal anti-IgE antibody therapy with, omalizumab. In patients with recurrent bacterial infections of the sinopulmonary tract, the basic humoral immune system testing includes measuring quantitative immunoglobulins (IgG, IgA, and IgM) and comparing them to age-matched normal ranges. Most clinical laboratories use nephelometry to measure immunoglobulin levels quantitatively. Nephelometry detects either the rate or the end point of soluble immune complex formation (the IgG in sera complexes with an anti-IgG antibody forming a classic immunoprecipitation reaction) by monitoring the scatter of transmitted light. The most common method for the screening of cellular immunodeficiency involved the measurement of the absolute and relative representation of the major lymphocyte subsets, T-cells, T-helper cells, T-cytotoxic cells, B-cells and NK-cells.

Skin testing versus radioallergosorbent testing for indoor allergens

BackgroundSkin testing (ST) is the most common screening method for allergy evaluation. Measurement of serum specific IgE is also commonly used, but less so by allergists than by other practitioners. The sensitivity and specificity of these testing methods may vary by type of causative allergen and type of allergic manifestation. We compared ST reactivity with serum specific IgE antibodies to common indoor allergens in patients with respiratory allergies.Methods118 patients (3 mo-58 yr, mean 12 yr) with allergic rhinitis and/or bronchial asthma had percutaneous skin testing (PST) supplemented by intradermal testing (ID) with those allergens suspected by history but showed negative PST. The sera were tested blindly for specific IgE antibodies by the radioallergosorbent test (Phadebas RAST). The allergens were D. farinae (118), cockroach (60), cat epithelium (90), and dog epidermal (90). Test results were scored 0–4; ST ≥ 2 + and RAST ≥ 1 + were considered positive.ResultsThe two tests were in agreement (i.e., either both positive or both negative) in 52.2% (dog epidermal) to 62.2% (cat epithelium). When RAST was positive, ST was positive in 80% (dog epidermal) to 100% (cockroach mix). When ST was positive, RAST was positive in 16.3% (dog epidermal) to 50.0% (D. farinae). When RAST was negative, ST was positive in 48.5% (cat epithelium) to 69.6% (D. farinae). When ST was negative, RAST was positive in 0% (cockroach) to 5.6% (cat epithelium). The scores of ST and RAST showed weak to moderate correlation (r = 0.24 to 0.54). Regardless of history of symptoms on exposure, ST was superior to RAST in detecting sensitization to cat epithelium and dog epidermal.ConclusionFor all four indoor allergens tested, ST was more sensitive than RAST. When both tests were positive, their scores showed poor correlation. Sensitizations to cat epithelium and dog epidermal are common, even in subjects who claimed no direct exposure.

IgE antibody in the serum--detection and diagnostic significance.

IgE antibody in the serum--detection and diagnostic significance.

IS THE PREVALENCE OF SPECIFIC IgE TO CLASSICAL INHALANT AEROALLERGENS AMONG PATIENTS WITH RESPIRATORY ALLERGY CHANGING? EVIDENCE FROM TWO SURVEYS 15 YEARS APART

Objective: The aim of this study was to evaluate the relative frequencies of sensitisation to four common inhalant allergens in two atopic populations suffering from asthma and/or rhinitis. One had been studied in the period of 1975 till 1979, and a second population was evaluated between 1992 and 1995.Data sources: At both time periods patients with inhalant allergy and visiting our outpatient clinic were included. Quantification of IgE to Dermatophagoides pteronyssinus, birch, timothy grass, and mugwort was performed via the Phadebas RAST technique (Pharmacia, Brussels, Belgium).Results: In patients suffering from respiratory allergy the frequency of birch pollen sensitisation significantly increased from 13 % in the period 1975-1979 to 34 % in the period 1992-1995. In contrast, the frequency of house dust mite, timothy grass pollen, and mugwort pollen sensitisation remained almost unchanged. The increase was not associated with an increase in the birch pollen count.Conclusion: Birch pollen hypersensitivity has almost tripled among atopic subjects during the last 2 decades. The exact mechanisms for this increase remain to be evaluated.

Two-dimensional electrophoresis of Malassezia allergens for atopic dermatitis and isolation of Mal f 4 homologs with mitochondrial malate dehydrogenase.

The yeast Malassezia furfur is a natural inhabitant of the human skin microflora that induces an allergic reaction in atopic dermatitis. To identify allergens of M. furfur, we separated a crude preparation of M. furfur antigens as discrete spots by 2-D PAGE and detected IgE-binding proteins using sera of atopic dermatitis patients. We identified the known allergens, Mal f 2 and Mal f 3, and determined N-terminal amino acid sequences of six new IgE-binding proteins including Mal f 4. The cDNA and genomic DNA encoding Mal f 4 were cloned and sequenced. The gene was mitochondrial malate dehydrogenase and encoded Mal f 4 composed of 315 amino acids and a signal sequence of 27 amino acids. We purified Mal f 4, which had a molecular mass of 35 kDa from a membrane fraction of a lysate of cultured cells. Thirty of 36 M. furfur-allergic atopic dermatitis patients (83.3%) had elevated serum levels of IgE to purified Mal f 4, indicating that Mal f 4 is a major allergen. There was a significant correlation of the Phadebas RAST unit values of Mal f 4 and the crude antigen, but not between Mal f 4 and the known allergen Mal f 2.

Effects of maternal dietary avoidance during lactation on allergy in children at 10 years of age

This study investigated the long-term effects of maternal dietary avoidance during lactation on the occurrence of atopic symptoms, development of immunoglobulin E (IgE) antibodies to food and inhaled allergens and occurrence of positive skin-prick tests (SPT) in 65 children with a family history of atopy whose mothers adhered to a diet devoid of eggs, cow's milk and fish during the first 3 months of lactation (D group) and in a matched group of 50 children with mothers not practising such a diet (ND group). The diets of the D and ND children were similar. All children attended 7 follow-ups from the age of 3 months to the age of 10 y. After the first follow-up there was a 100% retention of participants. The results of the seventh follow-up at 10 y are presented. Total IgE values and IgE antibodies to seven food and seven inhaled allergens were determined by the Phadebas IgE CAP and the Phadebas RAST, respectively. SPT were conducted for five food and seven inhaled allergens. High rates of atopic symptoms occurred in both groups, but there were no differences between the groups. Sensitization to the three foods avoided by the mothers during lactation was similar, but the overall test reactivity to foods was lower in the D group. Sensitization to inhaled allergens was similar in the two groups. During the 10 y of follow-up, there was no difference between the groups in the occurrence of indoor furred animals, tobacco smoking, changes in heredity for atopy or development of total IgE, but a higher rate of maternal sensitization was found in the ND group, as judged by a screening test for IgE antibodies to inhalants (Phadiatop). The results do not support general recommendations to implement prophylactic maternal dietary avoidance during lactation in allergy-prone families.

Specific IgE to isocyanates: A useful diagnostic role in occupational asthma

Background: Isocyanates are the most frequent cause of occupational asthma in industrialized countries. Objective: We sought to investigate the utility of specific IgE measurement in the diagnosis of isocyanate-induced asthma. Methods: Fifty-eight of 101 patients referred for investigation were diagnosed as having isocyanate-induced occupational asthma by means of history, serial peak flow records, and bronchial provocation tests. Specific IgE antibodies to toluene diisocyanate:human serum albumin (HSA), diphenylmethane diisocyanate:HSA, and hexamethylene diisocyanate:HSA were measured in all patients by Phadebas RAST. Results: Twenty patients had a RAST ratio of 2 or greater to at least one isocyanate. Thirteen (28%) of the 46 patients with a positive provocation test response had a RAST ratio of 2 or greater, and nine (20%) had a RAST ratio of 3 or greater. Raising the RAST cut-off from 2 or greater to 3 or greater reduced its sensitivity but increased the specificity of the test to 100%. RAST measurement was most likely to be positive within 30 days of exposure. Serial measurements suggested that the half-life of the IgE antibodies was approximately 6 months. Evidence of cross-reactivity between isocyanate RAST responses was found in eight subjects. Conclusion: Specific IgE to isocyanates is a more specific than sensitive index of occupational asthma. With a RAST score of 3 or greater, it is wholly specific and therefore diagnostic of isocyanate-induced asthma. The sensitivity of specific IgE measurement is highest when blood is taken less than 30 days from last exposure, which is consistent with the observed half-life.(J Allergy Clin Immunol 1998;101:709-15.)

The frequency and clinical significance of specific IgE to both wasp (Vespula) and honey-bee (Apis) venoms in the same patient.

Changeover from Phadebas RAST to Pharmacia AutoCAP increased double-positivity to both honey-bee and common wasp (vespula) venom in our patients. We examined the frequency of IgE double-positivity, its clinical relevance and utility in investigating potentially allergic patients. One hundred and eighty-two patients with hymenoptera allergy were tested using RAST (n = 51) and AutoCAP (n = 131) assays over 4 years. Patients had a history of reactions to vespulae (22), honey-bee (10) and unidentified hymenoptera (vespinae) (7). After changing from RAST to AutoCAP double-positivity increased from 10 (5/ 51) to 30% (39/131) (P < 0.01). RAST and CAP assays gave similar median class results (vespula = 3, honey-bee = 2). Thirty-six CAP patients had systemic reactions of Mueller grade II and above. In vespula-allergic double-positive subjects, high CAP classes (> or = class 3) to honey-bee were common (30%). In 25% the CAP classes were equal. In honey-bee-allergic subjects, all vespula venom CAP IgE was low titre (class 1 or 2) and 20% were equal for both venoms. In 43% of vespinae-allergic patients the CAP class was equal to both (class 2 and 3). In contrast, intradermal skin test double-positivity was uncommon. Double-negative skin test results were common in the CAP double-positive population (22% of honey-bee-allergic, 13% of vespula-allergic and 43% of vespinae-allergic patients). Vespula allergic patients have higher bee-venom IgE than vice versa. Twenty-seven per cent of CAP double-positive patients (representing 8% of all venom allergic patients tested over this period) had equal class IgE to both venoms which was not helpful in diagnosis. Combination of skin testing and CAP is unhelpful in only 5/37 (14%) of patients with double-positive serology. If used in isolation CAP may be misleading, especially if only one venom is tested. Identification of the causative venom must utilize both clinical history and skin testing in these double-positive patients, and challenge testing if indicated.

Hymenoptera sting anaphylaxis and urticaria pigmentosa: Clinical findings and results of venom immunotherapy in ten patients

Background: Occasional patients with urticaria pigmentosa and anaphylaxis after Hymenoptera stings have been described. In this situation the question arises: Is anaphylaxis IgE-mediated or induced by pharmacologic mediator release from mast cells? Methods: We investigated 10 patients with histologically confirmed urticaria pigmentosa and a history of anaphylaxis after honeybee or Vespula stings before and during immunotherapy with the respective venom. Results: In eight of 10 patients, an elevated serum tryptase level was found. In two of 10 patients, no venom-specific IgE could be detected by either skin tests or RAST. Five patients had no detectable venom-specific serum IgE, and in the remaining patients the level was low (<1 Phadebas RAST unit). Venom immunotherapy was well tolerated and caused only one mild systemic reaction in a patient during the dose increase phase. Six patients were re-stung while receiving venom immunotherapy: only one had a mild systemic reaction (angioedema) after a Vespula sting. Conclusion: Anaphylactic symptoms after Hymenoptera stings in patients with urticaria pigmentosa are most often IgE-mediated but can occasionally be observed in the absence of IgE sensitization to venom allergens. Venom immunotherapy can be safely and successfully used in patients with urticaria pigmentosa and sting anaphylaxis. (J Allergy Clin Immunol 1997;100:11-5.)

Selective allergic reactions to clavulanic acid

Clavulanic acid (CL) is a [Mactam antibiotic with weak antibacterial activity, but it is a potent inhibitor of [3-1actamases. In association with amoxycillin (AX) it has great antimicrobial activity and is increasingly prescribed in daily medical practice. We present two cases of selective adverse reactions to CL with good tolerance to other [3-1actam antibiotics in which a type I immunologic mechanism is probably implicated. To the best of our knowledge, these are the first reported cases of selective allergy to CL.

Appearance of atopic disease in relation to serum IgE antibodies in children followed up from birth for 4 to 15 years

Background: Few studies have addressed the relationship between sensitization and the development of atopic disease over many years.Objective: To study the temporal relationship between the appearance of IgE antibodies in serum and atopic disease, we studied 324 children from three different groups, who were followed up prospectively from birth for 4, 12, and 15 years, respectively.Methods: Serum samples were obtained at various ages and analyzed for IgE antibodies against egg white, cow's milk, wheat, animal dander, house dust mite, birch and timothy with Phadebas RAST (Kabi Pharmacia Diagnostics AB, Uppsala, Sweden) or Pharmacia CAP system. In addition, a screening test for atopy, the Phadiatop Paediatric test (Kabi Pharmacia Diagnostics AB) was performed. Presence of atopic disease was assessed by means of clinical examination, interviews, and questionnaires.Results: In 135 children IgE antibodies were detected at least once to at least one allergen. Antibodies to egg white appeared in 46 children before or at 2 years of age: in 57% of them IgE antibodies to inhalants developed within the next 2 years, and in 19 of 25 (76%) IgE antibodies to inhalants developed before or at 12 to 15 years. Antibodies to inhalant allergens appeared in 55 children during the first 4 years of life and in 64 before 12 to 15 years. Among the former 48% and among the latter 32% had previously detectable egg white antibodies. Atopic disease appeared before or at age 4 years in 80% of the 40 children with IgE antibodies against egg white up to 9 months of age and in 69% of the 58 children who had a positive Phadiatop Paediatric test result in infancy.Conclusions: IgE antibodies in children are usually associated with current or later topic disease. Sensitization to foods in infants is usually associated with appearance of IgE antibodies to inhalants later in life.

Influence of mite exposure on symptoms of mite-sensitive patients with asthma

We selected 22 patients who reported exacerbations of asthma symptoms or rhinitis in only one particular dwelling and were free of symptoms in another. These aggravations were observed several times, suggesting house dust-induced asthma. The 22 patients (12 women and 10 men; mean age, 25.4 ? 9.7 years) were monosensitized to Dermatophagoides pteronyssinus; they had a positive intradermal test result to D. pteronyssinus after injection of 0.04 ml of a lo-’ mg/ml D. pteronyssinus extract (Institut Pasteur, Paris, France) and a Phadebas Radio Allergo Sorbent Test (RAST, Pharmacia AB, Uppsala, Sweden) for D. pteronyssinus score of equal to or greater than 3. For each patient, two house dust samples were obtained. The first one was from the dwelling in which they were free of symptoms, and the second one was from the dwelling in which they had symptoms of asthma or rhinitis. The 44 house dust samples were collected by the patients, who vacuumed their mattresses for 2 minutes per square meter. Dust bags were stored at 4” C in sealed plastic bags. Semiquantitative guanine determination was performed with the Acarex-test (Allergopharma, Hamburg, Germany). According to the manufacturer, results are semiquantitatively expressed in four classes, for which the guanine content is indicated as 0, +, + +, or + + +. A Wilcoxon signed-rank test was performed to determine whether there was a significant difference between the Acarex-test results from the dwellings in which patients were free From “Service de Pneumologie, Hopital Civil, Hdpitaux Universitaires de Strasbourg; and %he Laboratoire d’EpidCmiologie et de Sante Publique, FacultC de Mtdecine, Strasbourg.

A new radioimmunoassay using a commercially available solid support for the detection of IgE antibodies against muscle relaxants

It is well established that muscle-relaxant drugs may be responsible for anaphylactoid reactions during anesthesia. In this study, we developed an in vitro test with a commercially available solid phase for the detection of specific IgE directed to the tertiary or quaternary ammonium groups of neuromuscular-blocking drugs. The solid-phase complex was p-aminophenylphosphoryl-choline (PAPPC) immobilized on agarose, and an RIA was performed with an antihuman IgE labeled with 125I. The results, expressed as the percentage of 125I-labeled anti-IgE linked to the solid phase, were at 0.41 ± 0.19 for 34 control sera from nonallergic healthy adults, with an upper limit estimated at 1%. The values obtained with the sera of 31 allergic patients ranged from 0.6% to 41% with a sensitivity of 97%. The specificity and the positive predictive value of the PAPPC RIA were 97% and 94%, respectively. These results were compared with results of other RIAs with morphine, trimethylamine, triethylamine immobilized on epoxy-activated Sepharose, and choline hydrochloride immobilized on Sepharose (quaternary ammonium Sepharose RIA) and with Phadebas RAST succinylcholine and Phadebas RAST alcuronium. The PAPPC RIA appears to be the most efficient test to screen sera for the presence of IgE antibodies directed to neuromuscular-blocking drugs. One major advantage is that this solid phase is commercially available and ready to use. This advantage will improve the accuracy in the comparison of the results with results from different laboratories.

Bee venom anti-idiotypic antibody is associated with protection in beekeepers and bee sting-sensitive patients receiving immunotherapy against allergic reactions

Bee venom (BV) anti-idiotypic (anti-Id) antibodies (Abs) were studied in nonreactive beekeepers, patients receiving BV immunotherapy (IT), and in patients with bee-sting hypersensitivity. Detection of serum anti-BV was determined either by the Phadebas RAST test for IgE and IgG concentrations or by isoelectric focusing followed by capillary blotting onto nitrocellulose membranes. Clonotypic analyses of Ab were made with specific probes for BV or BV anti-Id; 13 14 nonreactive multiple-sting beekeepers (93%; p = 0.00006) and 3 3 patients receiving BV IT (100%; p = 0.0026) had detectable amounts of BV anti-Id in serum, whereas five BV-sensitive patients (0%) and four ragweed-sensitive control patients (0%) did not. Beekeeper's serum containing BV anti-Id was found to recognize and bind to IgE anti-BV idiotype from two different patient sources and inhibit their reactions in a Phadebas RAST test in a dose-dependent manner. Nonreactive beekeepers generally had BV-specific IgE levels <0.35 PRU/ml in serum with detectable BV anti-Id. BV-allergic patients before IT had elevated BV-specific serum IgE levels, even in the presence of BV-spceific IgG >136 U/ml with no BV anti-Id present. These findings provide strong support for a protective role of BV anti-Id against bee sting-allergic reactions.

Do diagnostic procedures other than inhalation challenge predict immediate bronchial responses to inhaled allergen?

To investigate the relationships between allergen inhalation challenge and other diagnostic procedures, inhalation challenge with house dust (HD) allergen, intradermal skin tests with HD allergen, inhalation challenge with methacholine and circulating HD allergen-specific IgE levels were examined in 104 patients with bronchial asthma. Using the single exposure method, allergen inhalation challenge was performed. Forty-three patients had positive bronchial responses to allergen and 61 patients had negative bronchial responses. With serially diluted HD allergen (10(-3) to 10(-6), w/v), skin-test sensitivity was expressed as the highest dilution required to produce a weal of more than 9 x 9 mm. With the continuous exposure method, bronchial responsiveness to methacholine was evaluated as the number of units of inhaled methacholine (PD35-Grs) from the start to the point at which Grs had decreased by 35% from its baseline value. The level of circulating HD allergen-specific IgE was measured with the Phadebas RAST system and the results were assessed as a RAST score. Using discriminant analysis, in which the independent variables were skin-test sensitivity, PD35-Grs and the RAST score, only in 30% of all patients was bronchial responsiveness to inhaled HD allergen predictable. Therefore, we suggest that inhalation challenge with allergen is an essential test for determining the role of a specific allergen in airways at present.

Use of the extended Phadebas RAST® panel in the diagnosis of mould allergy in asthmatic children

The clinical significance of mould allergens in Phadebas RAST panel was investigated in 121 asthmatic children. They were selected from a total population of 1649 patients. The patients were distributed into four groups, based on the combination of positive or negative skin prick tests (SPT) together with symptoms suggestive or not of mould sensitivity. Mould-specific IgE antibodies were investigated using the original RAST panel (Alternaria, Aspergillus, Candida, Cladosporium, Mucor and Penicillium) and a set of 10 additional mould-allergen discs (Aureobasidium, Botrytis, Curvularia, Epicoccum, Fusarium, Helminthosporium, Phoma, Rhizopus, Stemphylium and Trichoderma). The set of additional RAST discs revealed patients with mould-reaginic antibodies not found with the original RAST panel. This occurred in four of 49 (8.2%) RAST positive (class greater than or equal to 2) patients. The allergens most frequently positive were Cladosporium (in 28% of the patients), Candida (28%) and Helminthosporium (26%). A remarkable degree of simultaneous reactivity to almost all moulds tested was observed. Patients with multiple (greater than or equal to 7) mould sensitization were effectively pinpointed using any duplicate combination of Aureobasidium, Botrytis, Candida, Cladosporium, Helminthosporium, Penicillium and Stemphylium.

Sensitization in childhood atopic disease identified by Phadebas RAST, serum IgE and Phadiatop

A search for IgE antibodies was performed in 224 children, aged 0–15 yr, with symptoms compatible with IgE‐mediated allergy, employing total IgE. RAST with up to 17 allergens and the Phadiatop® test. Fiftysix of 113 children (50%), aged 0–3 yr, and 80 of 111 children (72%) aged 4–15 yr had specific IgE antibodies. The most common allergens during the first 4 yr were egg white, a mixture of nuts (hazel nut, peanut, almond, coconut and Brazil nut) and milk. During the 2nd yr of life inhalant allergens became more important. From the 3rd yr they became more common than food allergens as sensitizers. Among the children aged 4–15 yr timothy, cat and nut mix were the most common allergens. Among the children with specific IgE antibodies Phadiatop was positive in 58% of the children younger than 4 yr, and in 91% of the children over that age. Fifty‐three of the children with IgE antibodies against nut mix were further investigated for antibodies against hazel nut, peanut and almond, and 48 (91%) were positive against at least one of them. The parents of 41 of these patients answered a questionnaire about adverse symptoms against nuts, and 26 (63%) were aware of clinical sensitivity. In conclusion, IgE antibodies against food allergens dominated in children under 2 yr, and thereafter antibodies against inhalants became more important. An unexpectedly high prevalence of IgE antibodies against nut mixture was found. Phadiatop was a good screening method for identification of children 4 yr or older with IgE antibodies against inhalants.

Comparative evaluation between two immunoenzymatic techniques (FAST and Phadezym) and the Phadebas RAST in food allergy

The diagnosis of food IgE-dependent hypersensitivity is based on the demonstration of specific IgE, completed by provocation tests. Two immunoenzymatic techniques, the Phadezym and the FAST, are compared with the Phadebas RAST, in 86 sera (23 controls, 28 from patients with a reported food allergy and 35 with a positive RAST to a food allergen). The within-run variation coefficient of class 0-2 sera was 9% for the Phadebas RAST, and higher than 20% for the Phadezym and the FAST. It was in order of 8.7%, 9.4% and of 17.6% respectively for Phadebas RAST, Phadezym and FAST when estimated with class 3-4 sera. The specificity was higher than 95% for the three techniques. The sensitivity was 75% for Phadebas and 43% for Phadezym and FAST. The FAST test is much less sensitive with allergens of vegetal origin than those of animal origin (P less than 0.01). This work indicates the high percentage of false negative results of immunoenzymatic techniques when food extracts are tested. This could be explained either by an enzyme-substrate reaction or by a non-specific inhibition of the enzyme linked to the anti-IgE IgG.

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.

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.