Cautions

This rapid polymerase chain reaction (PCR) assay detects Mycobacterium tuberculosis complex nucleic acid and, therefore, does not distinguish between viable, disease-related organisms and nucleic acid persisting from prior infection. Test results should be correlated with patient symptoms and clinical presentation before a definitive diagnosis is made.

A negative result does not rule out the presence of M tuberculosis complex or active disease because the organism may be present at levels below the limit of detection for this assay.

This test has not been studied for use with specimens from patients being treated with antituberculous agents and, therefore, should not be used to determine bacteriologic cure or to monitor response to therapy. It is not known how long the PCR assay can remain positive following treatment for M tuberculosis.

The sensitivity of this test from formalin-fixed, paraffin-embedded tissue is approximately 63%; therefore, testing of additional specimens should be considered if the result from the first specimen is negative.

A mycobacterial culture on a non-formalin-fixed specimen must always be performed in addition to the PCR test when non-fixed specimen is available. If your facility is unable to perform a mycobacterial culture, CTB / Mycobacteria and Nocardia Culture, Varies  should be ordered.

The sensitivity of the PCR assay from acid-fast smear positive specimens is approximately 96% compared to mycobacterial culture, but sensitivity of the PCR from a smear negative specimen is lower, and a negative result does not rule out M tuberculosis complex.