Optimal test technique for most allergens is lacking. Despite technological progress in the 20th century, patch tests are habitually still assessed visually. Morphology of definite positive patch tests is unknown, reflected by various reading scales available and false-positive tests.
Visual assessments are subjective rendering questionable the reliability of test readings.
Objective non-invasive assessments may be an alternative to such assessments or support them. This study uses in vitro experiments with simulated patch tests to investigate various factors that may affect LDPI readings of patch tests with the goal of providing LDPI set-up models for readings of patch tests on humans. Apart from readings of simulated tests, more than 40,000 readings were performed on 71 subjects. Transparent patches and application devices made possible assessment of patches during their application. Measurements of perfusion over time made possible charting and comparison of variable perfusion profiles among subjects tested with identical tests.