Evaluation of Xpert® MTB/RIF and DetermineTM TB LAM assay for the diagnosis of extra-pulmonary tuberculosis at Jimma University Medical Center, Southwest Ethiopia

Abstract

Background: Ethiopia is one of the high burden countries for EPTB. Conventional techniques have low sensitivity for diagnosis of extra pulmonary tuberculosis (EPTB) due to its paucibacillary nature. Thus this study is aimed to evaluate the diagnostic performance of Xpert MTB/RIF and Urine-LAM assay for the diagnosis of EPTB. Methods: An institution based cross-sectional study was conducted from April to October 2019. A total of 147 patients suspected for EPTB, including 23 HIV positive participants were enrolled. Socio demographic data were collected by a questionnaire. Extra-pulmonary samples were collected from all presumptive EPTB cases. From 126 study participants, urine sample were collected. All site-specific specimens were processed and tested by fluorescent microscopy, Xpert test and LJ culture whereas urine samples were tested by only Determine TB LAM test (Alere Inc, Waltham, USA). Clinical data’s such as HIV status, clinician’s decision to start anti TB treatment and treatment response were collected from patient’s medical records. Sensitivity and specificity of Xpert and TB LAM tests were calculated by comparing them with culture alone and with composite reference standard (CRS), which comprises smear microscopy, culture and anti TB treatment response results. Results: There were 37 overall EPTB cases (23 confirmed and 14 probable). The positivity rate of smear microscopy, Xpert and culture were 8.2%, 11% and 15.6% respectively. LAM test detects 13.5% of 126 participants. The sensitivity and specificity of Xpert test comparing to culture was 69.5% and 100% respectively; and its sensitivity and specificity were decreased to 43.2% and 100% respectively with the highest sensitivity for abscess (85.7%) and lower sensitivity for plural fluid (14.2%) with 100% specificity for all specimen types, compared to CRS. The sensitivity and specificity of LAM test comparing to culture was 35% and 91.3% respectively; and comparing to CRS it was 30.6% and 93.3% respectively with the highest sensitivity for HIV co-infected participants, 66.7%. Comparing with CRS the combination of Xpert and TB LAM test detected 61.1% of all TB participants and 83.3% of HIV co-infected TB cases. Conclusions: Determine TB LAM test has low sensitivity for EPTB diagnosis but, the combination of TB LAM and Xpert test could improve sensitivity of EPTB diagnosis and could replace culture, which is time consuming and less use for early diagnosis and treatment of EPTB cases.