Evaluation of the diagnostic value of Xpert Mycobacterium tuberculosis/rifampin assay in extrapulmonary ;tuberculosis / 中华传染病杂志

ABSTRACT

Objective To detect Mycobacterium tuberculosis (MTB)and its resistance against rifampin (RIF ) by applying Xpert MTB/RIF assay in the clinical samples from patients with extrapulmonary tuberculosis,and to discuss the value of this assay in extrapulmonary tuberculosis. Methods Totally 300 clinical samples from the patients who were highly suspected with extrapulmonary tuberculosis and hospitalized in Department of Tuberculosis Section,Shanghai Public Health Clinical Center of Fudan University from May 2014 to May 2015 were collected.Smear and fluorescence staining microscopy,MGIT 960 BACTEC liquid culture,Xpert MTB/RIF assay were applied to detect MTB in these samples.Meanwhile,all the patients received the peripheral blood T-cell spot of tuberculosis test (T-SPOT.TB).The sensitivity and specificity of Xpert MTB/RIF assay for MTB and its resistance against rifampin (RIF)in extrapulmonary tuberculosis samples were evaluated.The measurement data of two independent samples were analyzed by using t test and enumeration data were analyzed by usingχ2 test.Results Totally 282 out of 300 clinical samples from patients with extrapulmonary tuberculosis were included in this study,and 62.7% were male with average age of (32.1 ±24.6 )years and 37.3%were female with average age of (37.8 ±21 .0)years.When MGIT 960 BACTEC liquid culture results were considered as standard diagnosis,the sensitivity,specificity,positive predictive value and negative predictive value of Xpert MTB/RIF assay were 53.8% (95 %CI :37.4%—69.6%),100.0% (95 %CI :86.3%—100.0%),100.0% (95 %CI :80.8%—100.0%)and 63.3% (95 %CI :48.3%—76.2%), respectively.The sensitivity of Xpert MTB/RIF assay in smear-positive/culture-positive samples was 92.3% (95 %CI :62.1 %— 99.6%),while that in smear-negative/culture-positive samples was only 34.6% (95 %CI :17.9%— 55 .6%).Xpert MTB/RIF assay had advantage for detecting MTB in fine needle aspirates,pus,stool and urine,but not in serous effusion and cerebrospinal fluid.However,the sensitivities of MGIT BACTEC 960 liquid culture,fluorescence smear and T-SPOT.TB were 25 .8%, 21 .8% and 70.2%,respectively,and the specificities were 95 .5 %,90.3% and 51 .6%,respectively. The diagnostic value of Xpert MTB/RIF assay was not significantly different from those of MGIT BACTEC 960 liquid culture and fluorescence smear (χ2 =0.61 and 3.45 ,respectively;both P >0.05 ), while it was significantly different from T-SPOT.TB (χ2 =50.58,P <0.05).The sensitivity of T-SPOT. TB was significantly superior to Xpert MTB/RIF assay,but the specificity was relatively low.The sensitivity and specificity of Xpert MTB/RIF assay in RIF resistance detection were 71 .4% (95 %CI :30.3%—94.9%)and 100.0% (95 %CI :86.7%—100.0%),respectively.Conclusions The sensitivity and specificity of Xpert MTB/RIF assay in detecting MTB in fine needle aspirates,pus,stool and urine are relatively high,but not in serous effusion and cerebrospinal fluid.However,the pros of rapid detection and the ability of detecting RIF resistance are useful for the diagnose of extrapulmonary tuberculosis in clinical settings.