Figure 5.

Cycle-threshold (Ct) cutoff for smear-positive samples. The receiver operating characteristic (ROC) of Mycobacterium tuberculosis Ct as a test for smear-positive sputum is shown. Only tests with an internal control Ct less than 34 were included. Smear positivity was defined as all concentrated sputum samples that were grade 1+ or greater. The gray line indicates the ROC curve. The black circles indicate 1-Ct increments on the ROC curve, and black circles with a black triangle indicate each 5th Ct as labeled.