Utility of MPT64 antigen detection test for diagnosis of HIV coinfected extrapulmonary tuberculosis in Tanzania

<b>Objective:</b> Diagnosing extrapulmonary tuberculosis (EPTB) is a challenge. HIV coinfection adds to the challenge. Routine tests including Xpert MTB/RIF assay (Xpert) have low sensitivity highlighting the need for better diagnostics. We have developed a better test based on detection of Mycobacterium tuberculosis complex specific antigen MPT64, by immunohistochemistry, from biopsies, biological fluids, and fine needle aspirates. The objective was to validate the MPT64 antigen detection test for diagnosis of EPTB in HIV/TB coinfection <b>Methods:</b> 263 presumptive EPTB cases in Mbeya Zonal Referral Hospital, Tanzania, were prospectively enrolled between April 2016-July 2017. Patients were followed up from diagnosis to completion of treatment. Samples including fluids and aspirates from any suspected EPTB site were taken. All the samples underwent routine diagnostic work up; AFB microscopy, culture, histopathology and Xpert. The MPT64 test was performed on all samples. A composite reference standard including Xpert, culture, AFB microscopy, histology/cytology findings and response to anti-TB therapy was used to define TB cases <b>Results:</b> Of the 263 patients, 105 were defined as having EPTB; 48 TB adenitis, 21 peritonitis, 14 multiorgan, 11 pleuritis, 5 meningitis, 4 other, 2 disseminated. 35% of the EPTB cases were HIV positive. Among HIV positive and negative cases sensitivity for MPT64 was 90% &amp; 95%, Xpert 30% &amp; 42%, culture 22% &amp; 44%. Pooled sensitivity for all EPTB cases for MPT64 was 94%, Xpert 38%, culture 36%. The specificity was 86%, 99% and 100%, respectively <b>Conclusions:</b> The MPT64 test is better than routine tests for diagnosing EPTB. It performs well irrespective of HIV status.