Furthermore, differences in technique of performing SPTs (inter-observer variability) contribute to the variation in wheal size.
How to use spt psiphon 3 2016 skin#
To even further increase the accuracy of SPT results, the histamine-induced wheal size of the positive control might be considered as well to correct for skin histamine sensitivity. For this reason, a more advanced scanning method for SPT measurement has been applied for more than a decade in the Erasmus Medical Centre in Rotterdam. However, with this method, it is implicitly assumed that the wheal may be described reasonably well by an ellipse or circle, which is not always the case in practice and this method is prone to errors. In clinical practice and in most academic research, it is common to characterize the wheal shape by the ‘average diameter’.
The outcome of the SPT can result in a variety of wheal shapes, and there are several methods to measure these outcomes. Tests to measure sensitisation comprise in vitro specific IgE (sIgE) determination and skin prick testing (SPT). Standard diagnostics for Type-I acute allergic reactions to foods are based on the patient’s history combined with sensitisation tests and, optionally, a food challenge test. 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. A HEP-index area of 0.4 is determined as cut-off value for a positive SPT. The ‘scanned area method’ is theoretically more accurate in determining the wheal area than the ‘average diameter method’ and is recommended in academic research. The four methods showed comparable accuracy in predicting cashew nut reactions in a DBPCFC. The four SPT methods yielded a comparable area under the curve (AUC) of 0.84, 0.85, 0.83 and 0.83, respectively. 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. ResultsĬharacterizing the wheal size by the average diameter method is inaccurate compared to scanning method. average diameter, area, HEP-index diameter, HEP-index area) were compared in a Receiver-Operating Characteristic (ROC) plot. The accuracy in predicting the outcome of the DBPCFC using four different SPT readings (i.e. In addition, the same data for the histamine-induced wheal were collected for each patient.
Per patient, the average diameter and scanned area of the wheal size were recorded. All patients underwent a DBPCFC with cashew nut. Methodsĭata of 172 children with cashew nut sensitisation were used for the analysis. 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. 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. A more accurate method is to scan the area of the wheal to calculate the actual size. A commonly used method is to characterize the wheal size by its ‘average diameter’. There are several methods to read skin prick test results in type-I allergy testing.
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