Diagnostic utility of Primary Line Probe Assay in Extrapulmonary Tuberculosis

Line probe assay and Cartridge Based Nucleic Acid Amplification Test are molecular method for rapid diagnosis of Tuberculosis. Doing First line Line Probe Assay also called Genotype MTBDR plus detects Rifampicin and Isoniazid resistance. LPA detects rifampicin resistance by detecting rpoB mutation and isoniazid resistance by detecting both katG and inhA mutation. First line LPA has shown a sensitivity and specificity for the detection of Rif resistance of 96.7% and 98.8%, respectively, and for the detection of H resistance, a sensitivity and specificity of 90.2% and 99.2%, respectively for pulmonary tuberculosis. At our centre, we tried to evaluate the utility of Line Probe Assay for Extrapulmonary Tuberculosis. Total of 67 extrapulmonary samples were sent which included 35 pleural biopsies, 11 lymph node biopsies, 5 pleural fluid samples, 15 pus samples from paraspinal abscess, 1 urine sample. LPA was positive in 16 pleural biopsies, 6 lymph nodes, 1 pleural fluid sample, 7 pus samples and 1 urine sample. The positive patients were compared with histopathology and mycobacterial culture. 20 pleural biopsies 10 lymph node biopsies had granulomatous inflammation suggestive of tuberculosis.2 pleural fluid, 10 pus samples and 1 urine sample were culture positive. So, out of 67 extrapulmonary samples, 43 had confirmed tuberculosis and Line probe assay was positive in 31 samples that is sensitivity of 72.09% and specificity of 100%. Line probe assay is found to have decent accuracy in not only diagnosing extrapulmonary tuberculosis but also knowing about the resistance pattern. Further more studies are needed for confirmation of the results.