Diagnosis of latent tuberculosis infection in candidates for kidney transplantation (comparison of two tests)

It is assumed that about 10% of individuals infected with Mycobacterium tuberculosis develop tuberculosis. The rate of tuberculosis in solid organ transplant recipients has been estimated to be 50-fold higher than in the general population. Candidates for solid organ transplantation are routinely screened for latent tuberculosis infection (LTBI). In this study we aimed to compare Tuberculin Skin Test (TST) with QuantiFERON-TB Gold In-Tube (QFT) for the detection of LTBI in candidate for kidney transplantation. Between October 2009 and November 2010, 64 candidates for kidney transplant who referred to the transplant clinic in Imam Khomeini Hospital, were enrolled in the study. Patients were screened for LTBI with both QFT and TST. Concordance between two test results and variables associated with test discordance were assessed. The mean age of patients was 38.5 years (range 16-65); female/male ratio was 26/38. Positive results were found in 21.9% and 21.9%, by TST and QFT, respectively. Four patients (6.3%) had indeterminate QFT. Overall agreement between QFT and TST was 75% (k=0.28 and P=0.028). BCG vaccination and past positive TST were not associated with positive QFT result (P=0.13 and P=0.09 respectively). Overall agreement between test results was fair. Comparison among test results showed that TST andQFT can be used interchangeably for latent TB screening in kidney transplant candidates. The decision to select QFT or TST will depend on the purpose of testing and resource availability.