Role of GeneXpert in the diagnosis of extrapulmonary tuberculosis

Abstract

The World Health Organization endorsed the cartridge-based nucleic acid amplification test Xpert MTB/RIF (GXP) for the diagnosis of tuberculosis (TB). Studies about GXP efficiency in extrapulmonary TB (EPTB) are scarce. Hence, we decided to study the role of GXP in EPTB. This prospective observational study, conducted in the pulmonary medicine department of a tertiary care hospital after ethics committee permission, recruited 200 EPTB patients. The diagnosis of TB was achieved with the help of clinico-radiological correlation with microbiological test positivity. Acid-fast bacilli (AFB) culture was treated as the comparative gold standard. Patients who had no or incomplete data were excluded from the study. Data was analyzed to calculate the sensitivity, specificity, positive predictive value, and negative predictive value for the diagnosis of TB and the detection of rifampicin resistance. The majority of cases were women (126 patients: 63%). The mean age was 23.71 years. On GXP, 130 (65%) had detected mycobacterium tuberculosis (MTB), and 70 (35%) did not. Adding AFB culture data, 168 (81.5%) showed microbiological evidence of TB, and 32 (18.5%) were negative. On the drug susceptibility test, 131 cases were rifampicin-sensitive, 32 were rifampicin-resistant TB, and in 5 cases, data was unavailable. The most common extrapulmonary site of involvement was the lymph node, with 94 patients (47%). The most common lymph node involved was the cervical lymph node, with 70 patients (74.5%). The sensitivity, specificity, positive predictive value, and negative predictive value of GXP in EPTB collectively were 76.68%, 86.48%, 96%, and 45.7%, respectively. GXP is useful for the rapid detection of EPTB and the identification of rifampicin resistance, especially in a high-prevalence country like India.