The current order in which BAT can be used in penicillin allergy testing, according to European guidelines, is before ST for patients with a high-risk history, and after ST for low-risk patients (14). However, although the sensitivity of BAT was better than skin prick testing (51% vs 30%), sensitivity still remains extremely low. As the specificity of BAT is lower than skin testing (89% vs 97%), this paper does not provide strong evidence for the use of BAT to improve accuracy of investigations in penicillin allergy.
A questionnaire from 2007 with responses from 82 allergists across the world suggested 54% of responders used BAT in the work up of drug allergy hypersensitivity (48). A 2018 worldwide survey of the cost of allergy assessment, which included responses from 51 allergists, found the median cost for BAT was $129 (all values here given in US$ and adjusted for inflation to allow direct comparison), with only DPT costing more ($273) (49). Even with the cost of DPT, economic evaluations in both European and American healthcare systems have repeatedly concluded that widespread penicillin allergy testing with ST and DPT would be cost saving due to fewer courses of antibiotics, fewer outpatient visits and a need for fewer in hospital days (50, 51). Savings ranged from $50 to $7133 depending on the model used. One potential use of BAT might be to further decrease the costs of testing by decreasing the number of costly, and inevitably risky, DPT that need to be performed.
The 2020 EAACI position paper on beta-lactam allergy diagnosis suggests that “it is advisable to perform in vitro tests in addition to ST in high-risk patients in order to improve the sensitivity of the allergy workup and thus reduce the need for DPT”, but does not clarifying if one or both tests should be done, or which test is preferred (12). BAT shows clearly improved sensitivity above sIgE (51% vs 19%), (8). However, including BAT and sIgE with their respective specificity of 89% and 97%, would still mean a small proportion of patients may erroneously be considered positive for penicillin allergy after optimal assessment, despite being able to tolerate penicillin. For BAT to become a routine part of the diagnostic work up for penicillin, it must either have a sensitivity that is high enough for it to be used as a screening test, or a specificity higher than skin test or sIgE (>97%).