Figure 5. Device evaluation for sensitivity and specificity using surface-modified microfluidic chip.

(A) Passing-Bablok and (B) Bland-Altman analyses to compare the concentration of CD4⁺ T-cells obtained from the smartphone-based CD4⁺ T cell counter when PBS samples with CD4⁺ T cell concentrations between 60 cells/μL and 1200 cells/μL (n=30) were used. The solid blue line represents the regression line, the black line represents the identity line, and the two red lines represent the confidence band of the regression line in the Passing-Bablok figure. In the Bland-Altman figure, the blue line shows the mean difference between the methods, and the green lines represent the 95% limits of agreement. The accuracy of the smartphone-based device for measuring CD4⁺ T cell concentration (C,D) was 93.3%, and 96.6% for 200 cells/μL and 500 cells/μL thresholds, respectively (n=30). The blue lines represent the threshold values for each criterion above which the sample is considered to be of normal quality. The threshold values were established based on the WHO guidelines for advanced disease treatment and ART initiation thresholds respectively.