Sensitivity and specificity values, their risk of bias and applicability concerns are presented for all 22 studies in Figure 2. The SI threshold for positivity varied across the publications (2, 2.5 and 3 were all used). An estimation of a summary receiver operator characteristic (SROC) curve was generated using results from all 22 studies (Figure 3). The Higgins’ I2 of heterogeneity was 55.3% with a 95% CI 27.9% - 72.4%, indicating moderate between-study heterogeneity, and tau2 equal to 0.2522 with a p-value <0.0001 of the Cochrane Q statistic suggests the result is statistically significant. Twelve of the studies which undertook flow cytometric analysis of whole blood and used an SI of 2 as positive threshold for the diagnostic test, (Figure 4). As a summary point should only be completed using methods with the same positive threshold, this allowed calculation of a summary point sensitivity of 51% (95% CI, 46% – 56%), and specificity of 89% (95% CI, 85% – 93%), AUC 0.666, I2 14.4% (95% CI, 0% - 54%), tau2 0, p =0.30 (Figure 4).