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Keywords:

  • atopy;
  • children;
  • IgE sensitisation;
  • Phadiatop Infant

Abstract

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. References

Background:  Correct diagnosis of immunoglobulin E (IgE)-mediated disease is the prerequisite for secondary allergy prevention during early childhood.

Objective:  To evaluate the diagnostic efficacy of a new blood test, Phadiatop® Infant, in detecting IgE sensitisation to food and inhalant allergens among children at 2 years of age.

Methods:  Children (n = 239) were followed prospectively from birth to 2 years of age for the presence of IgE sensitisation and the development of atopic manifestations. Immunoglobulin E sensitisation was evaluated by skin prick test (SPT) and analysis of allergen-specific IgE antibodies in plasma to food and inhalant allergens. The children were classified into three groups: IgE-sensitised, non-IgE sensitised and inconclusive, depending on SPT and allergen-specific IgE results.

Results:  Twenty-six (11%) of the children were classified as IgE-sensitised, 182 (76%) as non-IgE sensitised and 31 (13%) as inconclusive. Phadiatop Infant was positive in 50 (21%) of the children. Ten children (4%) with identified IgE antibodies against the selected food and inhalant allergens showed negative Phadiatop Infant. Three children showed positive Phadiatop Infant but were negative in the other tests performed. These results correspond to positive and negative predictive values for Phadiatop Infant of 89 and 99%, respectively. Children with clinical symptoms of atopic diseases had significantly increased levels for Phadiatop Infant (P < 0.01).

Conclusion:  Phadiatop Infant appears to be a reliable alternative to SPT and the measurement of allergen-specific IgE antibodies in plasma for detecting clinically important IgE sensitisation among children at 2 years of age.

Allergic disease has become a common reason for paediatric consultations in Western industrialized countries as the prevalence of allergic disease have increased markedly in these countries over the last decades (1). The reasons for this increase are still largely unknown, but it is evident that the development and expression of allergic disease are due to a combination of genetic and environmental factors (2, 3). Although several studies have shown this change in the prevalence of immunoglobulin E (IgE)-mediated diseases, it has been argued that greater awareness and an improved ability to diagnose atopic disease may account, at least in part, for this increase (4).

In early childhood, allergic reactions are often mediated via the development of IgE antibodies. Atopic dermatitis, gastrointestinal symptoms and recurrent wheezing dominate as diseases of possible allergic nature. Immunoglobulin E antibodies to food allergens are most frequent during the first 2–3 years of life, while IgE antibodies to inhalant allergens predominate later in life (2, 5). Allergic reactions to foods, mainly cow's milk and hen's egg, are therefore most common during the first years of life, whereas allergy to inhalant allergens occurs later in life (5–7). Low levels of allergen-specific IgE antibodies to food allergens are a common phenomenon during early childhood and may have no clinical importance (5, 6). However, the presence of IgE antibodies against hen's egg during early infancy has been shown to predict respiratory allergy (7). Furthermore, the prognosis for children with wheezing and positive in vitro and/or in vivo test results for IgE is poorer than for wheezing children with negative test results (8).

Correct diagnosis is the prerequisite for a proper understanding of the allergic disease (9–13). Such diagnosis is of great importance for the child and the family, enabling individualized appropriate treatment and recommendations and avoiding unnecessary concern.

Phadiatop Infant is a new blood test for the detection of IgE antibodies against common food and inhalant allergens among small children (14). The aim of this study was to evaluate the result of the determination of Phadiatop Infant in children in relation to IgE sensitisation and the development of symptoms of atopic disease during the first 2 years of life.

Material and methods

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. References

Subjects

Children (n = 239), 121 girls and 118 boys, were recruited for the study. The families had been asked during pregnancy to participate in the study. The children were part of a prospective study of children whose cytokine profiles during early infancy were evaluated and related to the development of atopic disease (15). The parental heredity for atopic disease was confirmed before delivery by skin prick test (SPT) and only those parents with a positive or a negative SPT confirming the parental case history were invited to participate in the study. For 99 children, both parents reported a history of bronchial asthma and/or allergic rhino-conjunctivitis. For 72 children, only the mother and for 68 children neither of the parents reported a history of respiratory allergic disease. The study was approved by the Human Ethics Committee at Huddinge University Hospital, Stockholm and the parents provided informed consent.

Clinical evaluation

The children were followed prospectively from birth to 2 years of age and were clinically evaluated at 6, 12, 18 and 24 months of age by the same paediatrician. The presence of allergic diseases was defined in each child. The following definitions of the various allergic diseases were used: Eczema was defined according to Hanifin and Rajka (16).

Probable bronchial asthma was defined as three or more episodes of wheezing, or any episode of wheezing if combined with a family history of allergic disease or other allergic symptoms in the child. Allergic rhino-conjunctivitis was defined as symptoms of rhinitis and/or conjunctivitis appearing at least twice after exposure to a particular allergen and unrelated to infection. Food allergy/acute urticaria was defined as the acute onset of symptoms such as skin reactions, wheezing, vomiting, or diarrhoea on more than one occasion after ingestion of or contact with a particular food or allergen.

Skin prick test (SPT)

The same nurse performed all SPTs according to the manufacturer's recommendation (ALK, Copenhagen, Denmark). SPT was performed with the following allergens: egg white (Soluprick 1/100 w/v), cod fish (Soluprick 1/20), peanut, (Soluprick 1/20), cow's milk (3% fat, standard milk), soybean protein (Soja Semp® Semper AB, Stockholm, Sweden), cat, dog, Dermatophagoides farinae, birch and timothy (Soluprick 10 HEP). Histamine chloride (10 mg/ml) was the positive control and the allergen diluent was the negative control. The SPT was considered positive if the wheal diameter after 15 min was ≥3 mm.

Allergen-specific IgE

Circulating IgE antibodies against egg white, codfish, peanut, cow's milk, soybean, cat, dog, D. farinae and birch and timothy pollens were determined with Pharmacia CAP SystemTM (Pharmacia Diagnostics AB, Uppsala, Sweden) in plasma collected at 2 years of age. An allergen-specific IgE antibody level ≥0.35 kUA/l was considered positive.

Phadiatop Infant

ImmunoCAPTM Phadiatop® Infant (Phadiatop Infant, Pharmacia Diagnostics AB, Uppsala, Sweden) is a new blood test designed to detect allergen-specific IgE antibodies in serum or plasma to food and inhalant allergens that are relevant to IgE sensitisation in young children (14). Phadiatop Infant was analysed quantitatively in plasma, collected at 2 years of age, using Pharmacia CAP SystemTM (Pharmacia Diagnostics AB, Uppsala, Sweden). The following allergens are included in the test; hen's egg, cow's milk, peanut, shrimp, Dermatophagoides pteronysssinus, cat, dog, birch, timothy, ragweed and wall pellitory (Parietaria judaica). The amount of serum required was 50 μl. Results were expressed as Pharmacia Arbitrary Units per litre (PAU/l) indicating the degree of sensitisation. Phadiatop Infant values ≥0.35 PAU/l were considered to indicate sensitisation and were coded as positive in all dichotomous analyses.

Atopic classification

The children were classified into three groups on the basis of the results from the SPT and the allergen-specific IgE analyses: IgE-sensitised, non-IgE sensitised and inconclusive. Thus, children with a positive SPT result for at least one allergen and at least one positive allergen-specific IgE test result (not necessarily against the same allergen) were classified as IgE-sensitised (17). Children with all test results negative in both SPT and the allergen-specific IgE analyses were classified as non-IgE sensitised. The classification inconclusive was used for children with at least one positive test result in either SPT or the allergen-specific IgE analyses and all test results negative in the other method. The classification procedure was performed blind in relation to the results for Phadiatop Infant.

Statistical methods

In the statistical analysis, IgE antibody concentrations of Phadiatop Infant <0.35 and >100 PAU/l were given the values 0.34 and 101 PAU/l, respectively. Differences between groups were evaluated using the chi-square analysis and IgE antibody concentrations were compared using the Wilcoxon rank sum test or, when appropriate, Kruskal–Wallis one-way analysis by ranks.

The diagnostic capacity of Phadiatop Infant was evaluated using ROC analysis, from which clinical performance characteristics were calculated. Odds ratios (OR) with 95% confidence intervals (95% CI) were calculated using multiple logistic regression analysis. Adjustments were made for allergic heredity. A logistic regression model associating the atopy classification and the quantitative levels for Phadiatop Infant was also calculated and the result presented as a probability curve. Computerized statistical analysis was carried out using SAS System V 8.02 and a P-value <0.05 was considered significant.

Results

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. References

IgE sensitisation

Demographic data for the participating children are presented in Table 1. Twenty-six (11%) of the 239 children were classified as IgE-sensitised and 182 (76%) were non-IgE sensitised. Of the 31 (13%) children classified as inconclusive, seven had at least one positive SPT but negative allergen-specific IgE results for the selected allergens. In contrast, 24 children had a negative SPT but were positive in the analysis of allergen-specific IgE antibodies in plasma. Sex ratios among the children in the different groups did not differ significantly, but biparental heredity significantly influenced the presence of IgE antibody sensitisation (P = 0.029).

Table 1.  Demographic data – sex, heredity and point prevalence of clinical symptoms of atopic disease at 2 years of age
 The whole cohortIgE- sensitisedNon-IgE sensitisedInconclusive
N%n%n%n%
Total2391002611182763113
Sex
 Boys11849124688481858
 Girls12151145494521342
Heredity group
 Biparental9941186967371445
 None68283125832723
 Maternal723051957311032
Clinical manifestation
 Asthma5322115371552
 Eczema98412195824198
 Rhino-conjunctivitis73313110
 Urticaria115635200
 Food allergy1561253100
 No symptoms1094642964094

The prevalence of IgE sensitisation to food allergens dominated (Table 2). Among inhalant allergens IgE antibodies to dog were most prevalent.

Table 2.  Number of children with positive skin prick test (SPT)* and allergen-specific IgE† in relation to Phadiatop Infant test results at 2 years of age
 Total (N)Positive allergen-specific IgE and positive SPTNegative allergen-specific IgE and positive SPTPositive allergen-specific IgE and negative SPT
Positive Phadiatop Infant (n)Negative Phadiatop Infant (n)Positive Phadiatop Infant (n)Negative Phadiatop Infant (n)Positive Phadiatop Infant (n)Negative Phadiatop Infant (n)
  1. *Wheal diameter ≥3 mm.

  2. †Allergen-specific IgE ≥0.35 kUA/l.

Cow's milk339 21165
Hen's egg209 4151
Peanut135 215 
Soybean5  1 4 
Fish3  1 2 
D. farinae2    2 
Cat95 112 
Dog125  16 
Birch931  5 
Timothy2    2 

Phadiatop Infant and IgE sensitisation

Phadiatop Infant was positive among 50 (21%) of the children (Table 3). There was no significant association between positive/negative tests in relation to sex, but the number of positive tests increased significantly (P = 0.004) among children with atopic heredity.

Table 3.  Quantitative results [Pharmacia Arbitrary Units per litre (PAU/l)] for Phadiatop Infant in plasma at 2 years of age in the IgE-sensitised, the non-IgE sensitised and the inconclusive groups of children
 Total (N)Positive Phadiatop InfantNegative Phadiatop Infant
N%MeanMin25th perc.Median75th perc.MaxN%
  1. Phadiatop Infant <0.35 PAU/l  =  0.34 PAU/l and >100 PAU/l  =  101 PAU/l.

IgE-sensitised262550.08.120.511.132.274.87101.0010.5
Non-IgE sensitised18236.00.470.360.360.460.580.5817994.7
Inconclusive312244.00.950.370.400.521.282.9894.8
Total23950100.04.510.360.501.132.40101.00189100.0

The results for Phadiatop Infant in relation to the SPT and allergen-specific IgE results for the individual allergens are presented in Table 2. Six of 33 children tested positive (SPT or allergen-specific IgE) for milk but had negative Phadiatop Infant test results. All these children had low plasma IgE antibody levels for milk (0.43–0.56 kUA/l) or a moderately positive SPT (4 mm). One of these six children was healthy, but the other five had clinical symptoms of atopic disease, mainly eczema, although none of them was allergic to cow's milk.

One child with a positive SPT (3 mm) for peanut and another child with positive allergen-specific IgE in plasma for hen's egg (0.42 kUA/l) were negative in Phadiatop Infant. Both had clinical symptoms of eczema, but neither presented with any signs, symptoms or history of food allergy. It should be emphasized that one child, classified as IgE-sensitised but negative in Phadiatop Infant, accounted for all three positive results for the inhalant allergens cat, dog and birch. Furthermore, the child had no clinical symptoms of atopic disease.

All children that showed positive SPT or allergen-specific IgE test results for fish, soybean, D. farinae or timothy were positive in Phadiatop Infant.

In the IgE-sensitised group, 25 of 26 children were positive in Phadiatop Infant (Table 3). Furthermore, among children classified as non-IgE sensitised (n = 182) all but three had a negative Phadiatop Infant. The ROC analysis gave an optimal cut-off at 0.35 kUA/l with a sensitivity of 96% and a specificity of 98%, corresponding to a positive predictive value of 89% and a negative predictive value of 99% for the presence of allergic disease. If all children with any type of sensitisation (IgE-sensitised + inconclusive group) were taken into account the sensitivity became 82% and specificity was still 98%.

The dichotomous evaluation analysis was also extended to a quantitative evaluation of the Phadiatop Infant levels (Table 3). There was a significant difference (P < 0.001) between the values for Phadiatop Infant obtained among the children in the three study groups. Only one child had a Phadiatop Infant value >100 PAU/l.

The association between the quantitative results for Phadiatop Infant and the atopic classification (IgE sensitisation) was then evaluated with a logistic regression model. The result expressed as a probability curve is presented in Fig. 1. Using the model, a Phadiatop Infant concentration of 0.74 PAU/l gives a probability of 90% of being classified as IgE-sensitised, as assessed by individual allergens in vivo and in vitro.

image

Figure 1. The association (incl. 95% CI) between the quantitative levels for Phadiatop Infant [Pharmacia Arbitrary Units per litre (PAU/l)] and the probability of IgE sensitisation [positive skin prick test (SPT) and positive allergen-specific IgE in plasma] among 208 children at 2 years of age.

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Clinical evaluation

The point prevalence of various clinical manifestations of atopic diseases among the children at 2 years of age is presented in Tables 1 and 4. One hundred and nine children were asymptomatic and 94 children had clinical symptoms of one atopic disease, while 36 children presented with symptoms of two or more atopic diseases. Eczema (n = 98) and probable bronchial asthma (n = 53) were most prevalent as clinical symptoms of atopic disease.

Table 4.  Quantitative results [Pharmacia Arbitrary Units per litre (PAU/l)] for Phadiatop Infant in relation to clinical manifestations of allergic diseases among children at 2 years of age
Clinical manifestation*Total (N)Positive Phadiatop InfantNegative Phadiatop Infant
N%MeanMin25th perc.Median75th perc.MaxN%
  1. *Note: A child could have one or several symptoms.

Asthma5316327.940.390.490.991.56101.003720
Eczema9833665.560.370.621.242.88101.006534
Rhino-conjunctivitis7483.960.641.263.156.658.8832
Urticaria1161218.720.640.772.005.93101.0053
Food allergy15122413.530.620.932.2012.12101.0032
No symptoms10913261.350.360.400.582.234.879651
One symptom9418363.140.370.460.962.3222.357640
Two or more symptoms3619387.960.430.641.324.43101.00179

Phadiatop Infant in relation to clinical manifestations of atopic disease

Children with clinical symptoms of atopic diseases had significantly increased levels for Phadiatop Infant (P < 0.01).

The point prevalence of different allergic diseases at 2 years of age was evaluated in relation to IgE classification (Fig. 2) and in relation to the quantitative results for Phadiatop Infant (Table 4). Three children in the non-IgE sensitised group showed positive Phadiatop Infant. They included two children with no atopic manifestation and one child with probable bronchial asthma. The values for Phadiatop Infant among these children were low (0.36, 0.46 and 0.58 PAU/l). The only child with negative Phadiatop Infant in the IgE-sensitised group had no symptoms of atopic disease.

image

Figure 2. The association in 239 children between clinical manifestations* of atopic disease, obtained Phadiatop Infant results and classification in IgE-sensitised, non-IgE sensitised or inconclusive at 2 years of age. The columns are split with the number of children with negative Phadiatop Infant on top of the number with a positive Phadiatop Infant.

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There was a positive association between any clinical symptom of atopic disease and positive Phadiatop Infant (OR 2.7, 95% CI 1.3–5.5). Furthermore, there was a trend in the association between the number of clinical manifestations of atopic diseases at 2 years of age and a positive Phadiatop Infant. Thus, among children with one and two or more atopic diseases Phadiatop Infant showed an OR of 1.7 (95% CI 0.8–3.7) and 6.7 (95% CI 2.7–16.6), respectively, compared with children without symptoms of atopic disease. Evaluation of the individual allergic phenotypes showed there was a significant association between positive test results with Phadiatop Infant and the presence of eczema (OR 3.2; 95% CI 1.6–6.3). In contrast there was no significant association between positive test results with Phadiatop Infant and probable bronchial asthma, probably indicating an infectious aetiology in several of the asthmatic children.

Discussion

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. References

Interest is increasing in testing children for allergies. The paediatric section of the European Academy of Allergology and Clinical Immunology (EAACI) has recently published a position paper aiming at stimulating allergy testing within paediatric allergology (9, 18). Recent studies have shown that the measurement of allergen-specific IgE antibodies can also be useful in early childhood (19, 20). Apart from measurements of IgE antibodies and allergen challenges there are no effective tools in the diagnosis of IgE-mediated allergic diseases (21). In this study we have evaluated the usefulness of Phadiatop Infant, a new blood test for the detection of IgE antibodies to food and inhalant allergens, among children at 2 years of age. The efficacy of Phadiatop Infant in differentiating children with and without IgE sensitisation was highly significant.

Quantitative measurements of IgE antibodies as a tool for more precise allergy testing are presently under investigation (19, 20). The present study gave a further opportunity to evaluate the quantitative capacity of Phadiatop Infant in young children. Thus, children with allergen-specific IgE antibodies in plasma and a positive SPT, as well as children with clinical manifestations of atopic disease, showed increased values for Phadiatop Infant compared to nonsensitised children and symptom-free children.

A logistic regression model was established associating the quantitative levels for Phadiatop Infant with the classification (IgE sensitisation) assessed in terms of individual allergens in plasma and SPT. It showed a probability of 90% for classification as IgE-sensitised if Phadiatop Infant had an IgE antibody concentration of at least 0.7 PAU/l. However, it should be emphasized that this analysis was performed on a selected and rather small group of children using IgE sensitisation as the decision criterion. Further studies are needed before our results can be generalized to the whole population.

Fifty-seven (24%) children in our study were sensitised against the selected allergens, but only 26 (46%) of these children showed both a positive SPT and the presence of allergen-specific IgE antibodies in plasma. As expected, IgE sensitisation to food allergens dominated over IgE sensitisation to inhalant allergens (22, 23). Phadiatop Infant detected all but ten of the cases of IgE sensitisation. In six of these ten cases Phadiatop Infant did not detect IgE sensitisation to cow's milk. This may indicate that Phadiatop Infant has a limited ability to detect low-grade IgE sensitisation to cow's milk. There were isolated cases of children with weak IgE sensitisation to other allergens but a negative Phadiatop Infant. Furthermore, it is known from several studies that IgE antibodies to food allergens frequently occur during infancy with no evident clinical importance, although some children may develop allergy subsequently (2, 5–7). An ongoing follow-up, when the children in our study are 5 years of age, will show whether these cases of low-grade IgE sensitisation at young ages are only temporary and without clinical importance, or whether they have any impact on the development of allergic phenotypes at older ages.

Eczema and probable bronchial asthma dominated, as expected, as isolated clinical symptoms of allergic diseases among the children studied. Clinical symptoms of allergic disease were more common among children with positive Phadiatop Infant than negative. The difference in the number of clinical symptoms of allergic diseases between children with positive Phadiatop Infant and negative was significant and most pronounced for eczema. Notably, all children with clinical symptoms of allergic diseases and classified as IgE-sensitised had a positive Phadiatop Infant. Conversely, all but one child with clinical symptoms of allergic disease but with negative in vivo and in vitro results for IgE sensitisation showed negative values for Phadiatop Infant. Our results indicate that in the clinical situation, with children that have symptoms of various allergic phenotypes, Phadiatop Infant appears to be a reliable alternative to SPT and the analysis of allergen-specific IgE antibodies to individual allergens in plasma when differentiating allergic children with and without IgE sensitisation. Besides, less serum is required for the analysis, which is not unimportant when testing children. Compared with SPT, Phadiatop Infant has a better reproducibility and is available for all care givers. A recent study points at the advantages of using specific IgE measurements in primary care (24).

This study was performed on children with maternal, biparental or no heredity of allergic diseases and the presence of atopic disease among the parents were carefully characterized. Furthermore, the children were followed prospectively; the presence of IgE sensitisation was evaluated objectively by both SPT and the analysis of IgE antibodies in plasma, and the children were classified without knowing the results for Phadiatop Infant. However, it should be emphasized that the clinical classification of allergic bronchial asthma at this young age is not easy, because wheezing at this age is mostly correlated with bronchial hyper-reactivity in combination with upper respiratory infections and not to IgE sensitisation (8). Another limitation of the study is that the presence of food allergy was based only on case history and SPT and not on food challenge.

In summary, our results indicate that the diagnostic capacity of Phadiatop Infant to detect IgE sensitisation among young children are promising, and equal to the results in previous studies with Phadiatop combined or not with the analysis of allergen-specific IgE antibodies to food allergens (25, 26). Furthermore, among children with clinical symptoms of various allergic phenotypes, e.g. eczema, Phadiatop Infant appears to adequately separate individuals with and without an atopic component of the disease.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. References

The study was supported by Pharmacia Diagnostics. The authors want to thank the families who participated in the study, Anna Stina Ander and Monica Nordlund at Sodersjukhuset for technical assistance, Lars Söderström and Lisbeth Alainentalo, Pharmacia Diagnostics, for statistical advice and assistance.

References

  1. Top of page
  2. Abstract
  3. Material and methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. References