Comparison of wheat and rye flour solutions for skin prick testing: a multi-centre study (Stad 1).
BACKGROUND
Skin prick testing (SPT) is the basic method for diagnosing IgE-mediated allergies. However, skin reactivity is related to the quality of allergen extracts, which are often poorly defined for occupational allergens.


OBJECTIVE
To compare wheat and rye flour SPT solutions from different producers.


METHODS
Standardized SPTs were performed in seven allergy centres with wheat and rye flour solutions from four producers in 125 symptomatic bakers. Optimal cut-off levels for weal sizes were assessed with the Youden Index. Comparisons between SPT results of different solutions were made with flour-specific IgE (sIgE) as the gold standard. Sensitivities, specificities, positive and negative predictive values, and test efficiencies were calculated and compared with McNemar and chi(2)-tests. The influence of the choice of the gold standard (sIgE or challenge) test was examined for 95 subjects. Additionally, SPT solutions were analysed for protein and antigen content.


RESULTS
The optimal cut-off level for all SPT solutions was a weal size of >or=1.5 mm. While differences between wheat and rye flours were small, differences between producers were important. Variability of sensitivities (0.31-0.96), negative predictive values (0.42-0.91), and test efficiencies (0.54-0.90) were higher than variations of specificities (0.74-1.00) and positive predictive values (0.88-1.00). Similar results were obtained when using challenge test results as the gold standard. Variability could be explained by the different antigen contents of the SPT solutions.


CONCLUSIONS
There is a wide variability of SPT solutions for wheat and rye flour from different producers, mainly with respect to sensitivities, negative predictive values, and test efficiencies. Improvement and standardization of SPT solutions used for the diagnosis of baker's asthma are highly recommended.
van Kampen
V
V
BGFA - Research Institute of Occupational Medicine, Ruhr University, Bochum, Germany. kampen@bgfa.de
Merget
R
R
Rabstein
S
S
Sander
I
I
Bruening
T
T
Broding
H C
HC
Keller
C
C
Muesken
H
H
Overlack
A
A
Schultze-Werninghaus
G
G
Walusiak
J
J
Raulf-Heimsoth
M
M
D000328:Adult; D052179:Antigens, Plant / Q000032:analysis / Q000276:immunology*; D019540:Area Under Curve; D001249:Asthma / Q000175:diagnosis / Q000276:immunology; D001985:Bronchial Provocation Tests; D005260:Female; D005433:Flour / Q000032:analysis*; D005512:Food Hypersensitivity / Q000175:diagnosis* / Q000276:immunology; D006801:Humans; D007073:Immunoglobulin E / Q000097:blood / Q000276:immunology; D008297:Male; D008875:Middle Aged; D009784:Occupational Diseases / Q000175:diagnosis / Q000276:immunology; D011237:Predictive Value of Tests; D011506:Proteins / Q000032:analysis; D012372:ROC Curve; D012434:Secale / Q000276:immunology*; D012680:Sensitivity and Specificity; D012882:Skin Tests / Q000379:methods; D014908:Triticum / Q000276:immunology; D021182:Wheat Hypersensitivity / Q000175:diagnosis / Q000276:immunology
D052179:Antigens, Plant; D011506:Proteins; D007073:Immunoglobulin E