Interaction between C-Tb and PPD given concomitantly in a split-body randomised controlled trial.

<h2>SETTING:</h2>Seven tuberculosis (TB) clinics in South Africa.<h2>OBJECTIVE:</h2>As both purified protein derivative (PPD) and a Mycobacterium tuberculosis-specific skin test (CTb) contain region of difference 1 (RD1) antigens, we conducted a study to evaluate whether there was anyinteraction between the two during concomitant and separate administration in patients with newly diagnosed culture-positive TB.<h2>DESIGN:</h2>Adult patients with active TB (<italic>n</italic> &equals; 456, 20&percnt; human immunodeficiency virus infected) were randomised to receive only C-Tb, only PPD, or concomitant injection of both C-Tb and PPD using the Mantoux technique. Indurations were read after 48&ndash;72 h. QuantiFERON&reg; -TB Gold In-Tube (QFT) was performed in tandem.<h2>RESULTS:</h2>Of the 456 study participants, 154 simultaneously received both C-Tb and PPD, 153 only C-Tb and 149 only PPD. There was no effect of concomitant injection of PPD on the mean C-Tb induration (19 mm, 95&percnt;CI 17&ndash;22 vs. 18 mm, 95&percnt;CI 16&ndash;21; <italic>P</italic> &equals; 0.91). In patients with active TB, C-Tb sensitivity (78&percnt;) was similar to PPD (81&percnt;) and QFT (84&percnt;; excluding 82/429 &lsqb;19&percnt;&rsqb; indeterminate results). All tests showed reduced sensitivity in participants with CD4 &lt;100 cells/&mu;l.<h2>CONCLUSION:</h2>In patients with active TB, there was no interaction between C-Tb and PPD during concomitant injection of both agents. Sensitivities were similar for PPD and C-Tb.