TUBERCULOSIS TEST
TUBERCULOSIS TEST By. Dr. Gemma Posas, IM-Pulmonology
In recent years M. tuberculosis infections have been increasing worldwide, especially in Eastern Europe and Asia. This worldwide increase in M. tuberculosis cases and appearance of drug-resistant strains continues to maintain tuberculosis as a great health risk to the population. Most MTB-related deaths could be prevented by early diagnosis and treatment. The diagnosis of TB due to Mycobacterium tuberculosis (MTB) is most commonly made by using microscopy and culture. However, the former has a low sensitivity and can provide at best only a preliminary diagnosis. The latter, requires about 6 to 8 weeks before a final diagnosis can be made. There is thus an urgent need for a rapid, safe, and verifiable method to establish the diagnosis of TB.
At present, Nucleic acid amplification techniques (NAATs) are the most promising development in TB diagnostics. These tests have been shown to have high specificity, but limited and variable sensitivity, especially for sputum smear-negative disease. Simplified versions of these assays with higher sensitivity are being developed (1). Nucleic acid (NA) amplification methods fall into 3 categories: Target amplification systems, Probe amplification systems, and Signal amplification (2).
An example of Target Amplification Method is the Polymerase Chain Reaction (PCR). Currently available at the Palawan MMG Multipurpose Cooperative Hospital Laboratory is the COBAS® TaqMan® MTB Test which utilizes real-time PCR technology (RT PCR). This is an in vitro nucleic acid amplification test for the qualitative detection of Mycobacterium tuberculosis (MTB) complex DNA in liquefied, decontaminated and concentrated human respiratory specimens, including sputum and bronchial alveolar lavages (BAL). The test utilizes the AMPLICOR® Analyzer respiratory specimen preparation kit for manual specimen preparation and the COBAS® TaqMan® 48 analyzer for automated amplification and detection. This test is based on two major processes: (1) manual specimen preparation to obtain MTB DNA; (2) simultaneous PCR amplification of target DNA using complementary primers, and detection of target DNA through cleavage of dual fluorescent dye-labeled oligonucleotide probes. Together, these processes permit the detection of MTB target amplified products (amplicon) and Mycobacterium Internal Control DNA, which is amplified and detected simultaneously with the specimen. The master mix reagent contains a primer pair that is used to amplify a genus-specific region of the chromosome and specificity for the M. tuberculosis complex is provided by a dual-labeled target detection probes that permit independent identification of MTB amplicon and Mycobacterium Internal Control amplicon (3).
Methods for the detection of mycobacteria are continuously being developed as scientist from all over the world try to propose a rapid, accurate and low-cost test. The presence of mycobacterial DNA is most commonly detected by PCR technique. However, certain inaccuracies also exist with these procedures, given by natural polymorphism or the inability of the methods to identify dead microorganisms. Advances in molecular biology offer the most promising methods for the future. Novel methods being developed are more and more rapid and accurate. Such methods will make it possible to reveal the dangerous mycobacterial diseases much more effectively and to initiate early, adequate and effective treatment of the diseases.
REFERENCES:
(1) World Health Organization. Guidelines for the programmatic management of drug resistant tuberculosis — 2011 updates. WHO/HIM/T6/2011. Geneva World Health Organization 2071.
(2) Sullivan, Donna C., Nucleic Acid Amplification Techniques. Division of Infectious Diseases University of Mississippi
Medical Center 2014.
(3) Document revision information, COBA se TaqMan® (product insert).