Tuberculosis other diagnostic studies

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mashal Awais, M.D.[2]; Alejandro Lemor, M.D. [3]


Apart from X-rays, CT scans, MRI, diagnostic studies that can be done in patients with tuberculosis are the Xpert MTB/RIF test, Adenosine Deaminase Test, and Nucleic Acid Amplification Test (NAAT).

Other Diagnostic Studies

Xpert MTB/RIF Test

  • Detects M. tuberculosis and rifampicin drug resistance simultaneously.
  • Results are available in less than 2 hours so the patient can be treated the same day of the test.
  • The bio-safety requirements and training are minimal.
  • It can be stored in non-conventional laboratories.

Adenosine Deaminase

It is an additional test in case of suspecting TB in a patient.[3]

Nucleic Acid Amplification Tests (NAAT) Adapted from CDC [4]

  • NAAT is a group of tests that use polymerase chain reaction (PCR) to detect a mycobacterial macromolecule.
  • These tests are variable regarding the accuracy and which macromolecule sequence they can detect.
  • The two most widely available tests are the amplified tubercle bacillus direct test (MTD, Gen-Probe) and Amplicor (Roche Diagnostics).
  • The CDC recommends that NAA testing should be performed on a respiratory specimen from each patient with signs and symptoms of active pulmonary TB disease for whom a diagnosis of TB is suspected, but has not been confirmed.
  • NAA testing cannot replace the value for AFB smear and culture.
  • A single positive NAA test result can support the diagnosis of TB during a patient for whom there's an inexpensive index of suspicion. This result should trigger reporting to public health officials, initiation of treatment if not already started, and vigorous efforts to get an isolate for drug susceptibility testing.
  • In a patient with little suspicion of getting active TB, one positive NAA test result should be viewed with suspicion (i.e., a possible false-positive result) and interpreted within the same way as one culture-positive result, i.e., by correlating the results with other diagnostic findings.
  • A single negative NAA test result should never be used as a specific test to exclude TB, especially in suspects with a moderate to high clinical suspicion of TB. However, the negative NAAT result may be used as additional information to help with making clinical decisions to establish a work-up for an alternate diagnosis or to prevent unnecessary use of TB medication in suspected cases.
  • The FDA-approved NAAT tests for TB have slightly less sensitivity than culture-isolation methods, and therefore the 15% -20% of U.S. TB cases that are reported with negative culture results can also have negative NAA test results. Thus, a negative NAA test result doesn't exclude the diagnosis of TB.
  • Further research is required before specific recommendations are often made on the utilization of NAAT testing within the diagnosis of TB in children who cannot produce sputum and within the diagnosis of extrapulmonary TB, although there's much scientific evidence of the utility of such testing in individual cases.


  1. "Availability of an Assay for Detecting Mycobacterium tuberculosis, Including Rifampin-Resistant Strains, and Considerations for Its Use — the United States, 2013".
  2. 2.0 2.1 "WHO Tuberculosis Diagnosis Xpert MTB/RIF Test 2013" (PDF).
  3. Farazi A, Moharamkhani A, Sofian M (2013). "Validity of serum adenosine deaminase in diagnosis of tuberculosis". Pan Afr Med J. 15: 133. doi:10.11604/pamj.2013.15.133.2100. PMC 3852508. PMID 24319523.
  4. "CDC Report of an Expert Consultation on the Uses of Nucleic Acid Amplification Tests for the Diagnosis of Tuberculosis".

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