Testing Algorithms for Mycobacterium tuberculosis Complex using Real Time- Polymerase Chain Reaction: When to implement GeneXpert assay?

Study Design: Traditionally, Mycobacterium tuberculosis complex (MTB-complex) is identified by conventional methods. However, molecular methods are now being used more often. The previous algorithm of acid fast bacilli (AFB) smear positive patients who were new to the Bureau of Clinical Laboratories (BCL) was run on the GeneXpert automatically. The Xpert® MTB/RIF assay, performed on the GeneXpert® Instrument Systems, is a qualitative, nested real-time polymerase chain reaction (PCR) in vitro diagnostic test for the detection of MTB-complex DNA in raw sputum or concentrated sputum sediment prepared from induced or expectorated sputum. In specimens where MTB-complex is detected, the Xpert MTB/RIF assay also detects the rifampinresistance associated mutations of the rpoB gene. This assay was used to test 551 tuberculosis specimens between January 8, 2015 and October 12, 2016 using the new algorithm that is based on AFB smear results in addition to physician requests. If a patient is AFB smear positive and is not on file at the BCL, PCR by GeneXpert is performed. If a patient is smear negative and a physician requests PCR by GeneXpert based on clinical presentation of the patient, PCR is also performed.