ELONA results of the ssDNA aptamer CSIR 2.11 tested as a detection reagent for active TB in sputum samples

DNA aptamers that bind to the CFP-10.ESAT-6 heterodimer were isolated. To assess their affinity and specificity to the heterodimer, aptamers were screened using an enzyme-linked oligonucleotide assay (ELONA). One suitable aptamer was evaluated by ELONA using sputum samples obtained from 20 TB patients and 48 control patients (those with latent TB infection, symptomatic non TB patients, and healthy laboratory volunteers). Culture positivity for <i>Mycobacterium tuberculosis</i> (Mtb) served as the reference standard. Accuracy and cut-points were evaluated using ROC curve analysis.Two donors gave a single sample each and were not detected as TB positive in the ELONA. Of the 13 donors that gave two sputum samples, two cases had both samples as positive and in three of the cases only the second sample gave a positive reading.The Youden’s index is one that selects the best trade-off between sensitivity and specificity using a ROC curve, and may not correspond to a cut-point that rules in or rules out disease.