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*The two commonest commercially available tests are the amplified tubercle bacillus direct test (MTD, Gen-Probe) and Amplicor (Roche Diagnostics). | *The two commonest commercially 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 being considered (i.e., TB suspect), but has not been established. | *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 being considered (i.e., TB suspect), but has not been established. | ||
*NAA testing doesn't replace the necessity for AFB smear and culture. All current guidelines and proposals for [[culture-based testing]] should remain in effect, especially recommended rotate times for culture and DST. | *[[NAA testing]] doesn't replace the necessity for AFB smear and culture. All current guidelines and proposals for [[culture-based testing]] should remain in effect, especially recommended rotate times for culture and DST. | ||
*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. | *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. | *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. | ||
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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]
Overview
Diagnostic studies that could be performed in patients with tuberculosis beside X-rays, CT scans, MRI are the Xpert MTB/RIF test, Adenosine Deaminase Test, and Nucleic Acid Amplification Test (NAAT).Other diagnostic studies that would be performed during a patient with tuberculosis are the Xpert MTB/RIF test, ADA Test, and macromolecule Amplification Test(NAAT).
Other Diagnostic Studies
Xpert MTB/RIF Test
- The Xpert MTB/RIF test is a molecular test that detects the DNA of the tubercule bacillus complex (MTBC) and also the genetic mutations related to resistance to rifampin (RMP) in unprocessed sputum and concentrated sputum sediments [1]
- WHO recommends the Xpert MTB/RIF test for the initial diagnosis of MDR-TB or HIV-TB co-infection.[2]
- The advantages of this rapid Tuberculosis test are the following:[2]
- 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 usually an additional test if tuberculosis is suspected in the patient.[3]
- ADA is used for diagnosing tuberculosis in endemic countries where TB diagnostic procedures are not affordable.
- isoenzymes are more accurate. For both pleural TB and TB meningitis , ADA has a high degree of sensitivity.
Nucleic Acid Amplification Tests (NAAT) Adapted from CDC [4]
- This is a heterogeneous group of tests that use polymerase chain reaction (PCR) to detect a mycobacterial macromolecule.
- These tests vary during which macromolecule sequence they detect and vary in their accuracy.
- The two commonest commercially 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 being considered (i.e., TB suspect), but has not been established.
- NAA testing doesn't replace the necessity for AFB smear and culture. All current guidelines and proposals for culture-based testing should remain in effect, especially recommended rotate times for culture and DST.
- 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. Rather, the negative NAA test result should be used as additional information to assist in making clinical decisions to expedite a work-up for an alternate diagnosis or to stop unnecessary use of TB treatment 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.
References
- ↑ "Availability of an Assay for Detecting Mycobacterium tuberculosis, Including Rifampin-Resistant Strains, and Considerations for Its Use — the United States, 2013".
- ↑ 2.0 2.1 "WHO Tuberculosis Diagnosis Xpert MTB/RIF Test 2013" (PDF).
- ↑ 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.
- ↑ "CDC Report of an Expert Consultation on the Uses of Nucleic Acid Amplification Tests for the Diagnosis of Tuberculosis".