Ability of a single CD4 at switch to second-line for first-line failure to predict VL.

<p>(a) in patients not receiving routine CD4 count monitoring (CDM: 20% >250 cells/mm3). (b) in patients receiving routine CD4 count monitoring (LCM: 2% >250 cells/mm3). Footnote 2 Receiver operator curves (ROC) show how the sensitivity and specificity of CD4 thresholds for predicting VL<400 copies/ml varies as CD4 increases from 1 to 788 (CDM) or 505 (LCM) cells/mm³. The straight line indicates performance no better than chance. The threshold with the greatest probability of correctly classifying each CD4 count according to whether it has VL<400 copies/ml or not is indicated with sensitivity (proportion with VL<400 c/ml who have CD4≥threshold), specificity (proportion with VL≥400 c/ml who have CD4