Comparison of culture, microscopic smear and molecular methods in diagnosis of tuberculosis

Tuberculosis (TB) is a public health problem worldwide, with the highest mortality . The development of nucleic acid-based tests for detection of Mycobacterium tuberculosis complex (MTBC) has significantly increased sensitivity compared to conventional smear microscopy and provides results within a matter of hours compared to weeks for solid culture, which is the current gold standart. The aim of this study was to compare the culture, microscopic smear and molecular method in the diagnosis of TB.

Seven hundred ninety specimens belonging to clinically suspected cases of TB were studied retrospectively. The specimens were grouped as respiratory and non-respiratory and the groups were compared for mycobacterial detection assays. The culture and the molecular diagnostic GeneXpert MTB/RIF (GX) assay method were compared.

When culture was used as the reference standart, 32 (4.05%) specimens were positive for MTBC. Of the 32 culture positive clinical specimens 24 (3.03%) were respiratory and 8 (1.01%) were non-respiratory specimens. All 24 of the 24 respiratory specimens were positive by the GX test, Seven of the eight non-respiratory specimens positive for culture were positive by GX assay. Five of the seven hundred fifty-eight samples of culture negative were positive with GX assay. Sensitivity and specificity of GX were found to be 96.8 % and 99.3 %, respectively.

Molecular methods to acquire time in diagnosis as well as the increase in linearity gives a different perspective to the diagnosis of tuberculosis. The GX assay has a diagnostic utility for rapid diagnosis of TB.