The time since the last reaction and BAT assessment also varied widely both between studies, and within studies. It was therefore not possible to undertake any sub-group analysis and comment on how this may have influenced the BAT outcome. As one potential use for BAT might be to investigate penicillin allergy in a person with a distant history of reaction, it would be important to know if a BAT result is reliable many years after the last penicillin exposure. A study published by Fernandez et al. showed that BAT reactivity decreased significantly even over a four-year study period (53). Only 1 of 41 patients was BAT positive at the four-year mark. When we consider this, along with the low sensitivity of the test from this meta-analysis, the clinical utility of BAT as a “rule-out” test may be limited. However, with its high specificity, BAT may be a good “rule-in” test and, if positive, could save patients from having a potentially harmful positive DPT.  Future studies looking at the use of BAT as a diagnostic test should be clear about the time from reaction for the samples analysed, as this may have a significant effect on the BAT outcome.
There is still an unmet clinical need for improved in vitro diagnostics in penicillin allergy. BAT represents one potential avenue for investigation, however the evidence shown here has low certainty and is not yet ready for clinical application. Any future work looking at the application of BAT in the diagnosis of penicillin allergy can use this result as a benchmark of current practice, and should use an SI threshold of 2 and aim to improve upon the sensitivity of 51% and specificity of 89%. The use of a minimum number of 500 basophils per test is supported by this work.
Data and template data collection forms can be made available or request with corresponding author.