Measurement and interpretation of skin prick test results

Abstract

BackgroundThere are several methods to read skin prick test results in type-I allergy testing. A commonly used method is to characterize the wheal size by its ‘average diameter’. A more accurate method is to scan the area of the wheal to calculate the actual size. In both methods, skin prick test (SPT) results can be corrected for histamine-sensitivity of the skin by dividing the results of the allergic reaction by the histamine control. The objectives of this study are to compare different techniques of quantifying SPT results, to determine a cut-off value for a positive SPT for histamine equivalent prick -index (HEP) area, and to study the accuracy of predicting cashew nut reactions in double-blind placebo-controlled food challenge (DBPCFC) tests with the different SPT methods.MethodsData of 172 children with cashew nut sensitisation were used for the analysis. All patients underwent a DBPCFC with cashew nut. Per patient, the average diameter and scanned area of the wheal size were recorded. In addition, the same data for the histamine-induced wheal were collected for each patient. The accuracy in predicting the outcome of the DBPCFC using four different SPT readings (i.e. average diameter, area, HEP-index diameter, HEP-index area) were compared in a Receiver-Operating Characteristic (ROC) plot.ResultsCharacterizing the wheal size by the average diameter method is inaccurate compared to scanning method. A wheal average diameter of 3 mm is generally considered as a positive SPT cut-off value and an equivalent HEP-index area cut-off value of 0.4 was calculated. The four SPT methods yielded a comparable area under the curve (AUC) of 0.84, 0.85, 0.83 and 0.83, respectively. The four methods showed comparable accuracy in predicting cashew nut reactions in a DBPCFC.ConclusionsThe ‘scanned area method’ is theoretically more accurate in determining the wheal area than the ‘average diameter method’ and is recommended in academic research. A HEP-index area of 0.4 is determined as cut-off value for a positive SPT. However, in clinical practice, the ‘average diameter method’ is also useful, because this method provides similar accuracy in predicting cashew nut allergic reactions in the DBPCFC.Trial registration: Trial number NTR3572

The effect of early growth patterns and lung function on the development of childhood asthma: a population based study

“…Postnatal questionnaires provided information on breastfeeding, day care attendance, lower respiratory tract infections and passive smoking in the first year. At the age of 10 years, inhalant allergic sensitisation for the five most common inhalant allergens (house dust mite, grass, birch, cat and dog) was determined by a skin prick test (ALK-Abelló, Almere, the Netherlands), using the ‘scanned area’ method 35. Length and weight at 10 years of age were measured and BMI (in kg/m 2 ) adjusted for age and sex was calculated 36…”

Cashew Nut Allergy: Clinical Relevance and Allergen Characterisation

“…To increase the accuracy of the SPT, the area of the allergen-induced wheal can be compared with the area of a histamine-induced wheal size (as positive control) to correct for skin histamine sensitivity. The ratio is defined as histamine equivalent prick (HEP) index [34]. Considering an average wheal diameter over 3 mm and HEP index area ≥0.4 as baseline for positive sensitization, van der Valk et al [32] reported a mean value of 3.02 of HEP index (range 0-15.16) in 164 of cashew nut allergic children.…”

“…cashew nut) and/or to confirm the allergy [28]. In general, individuals presenting a convincing medical history of cashew nut allergy, SPT of wheal diameter over 3 mm (HEP index ≥0.4) and/or serum-specific IgE of 0.35 kUA/L are often purposed for oral provocation tests (DBPCFC or OFC) with increasing doses of cashew nut [32,34]. The oral provocation tests are normally discontinued and considered positives when objective symptoms occur, when severe subjective symptoms persist (>1 h) or when subjective symptoms re-appear after second dose of the same challenge material [32].…”

Maternal folic acid use during pregnancy, methylenetetrahydrofolate reductase gene polymorphism, and child's lung function and asthma

“…22 We measured inhalant allergic sensitization by skin prick test using the "scanned area method", 23 for which detailed information is provided in the Appendix S1. Maternal weight and height were measured at enrollment.…”

“…The country of birth of parents was used to define the child's ethnicity. 22 We measured inhalant allergic sensitization by skin prick test using the "scanned area method", 23 for which detailed information is provided in the Appendix S1.…”