From the twenty-two manuscripts reporting both on sensitivity and specificity, six reported results for two different BAT assay types. 18 (64%) measured flow cytometric analysis of activation of basophils collected directly from the patient. Four (14%) measured sulfidoleukotriene production. Two (7%) measured histamine release, two (7%) undertook indirect observation, and two (7%) underwent a direct observation of where basophils morphology was examined under a microscope to determine activation. The different methods had similar sensitivity and specificity profiles as can be seen in comparison of SROC curves (Figure 6), and as seen by an even spread across the SROC curve of all 22 studies (Figure 3).
The minimum number of basophils required for a sample to be analysed was reported in 16 studies (73%) with a median value of 500 basophils required per sample, with a range from 200 -1000. Eleven studies that used an SI threshold of 2, and had details of the minimum number of basophils used in their assay, allowed an estimated summary points for sensitivity and specificity to be generated (Figure 4). The use of a minimum of 1000 basophils (sensitivity 0.58 (95% CI, 0.48-0.68) and specificity 0.91 (95% CI, 0.82 - 0.96)) per test did not confer any significant improvement in sensitivity or specificity over a minimum of 500 (sensitivity 0.44 (95% CI, 0.36 – 0.51) and specificity 0.91(95% CI, 0.80 – 0.96)).
Two papers directly compared CD63 and CD203c as markers of basophil activation and suggested that CD203c was potentially a better marker (25, 46). Statistical comparison of summary points could not be undertaken as one study did not define its positive result threshold.
All studies were of high or at least unclear risk of bias (RoB). The most frequent source of potential bias was due to the patient selection process with 14 of 22 studies (64%) rated as high risk in this domain, Figure 2. This was largely due to the fact that most studies did not specify how patients were identified.