Tuberculosis screening
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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]; Marjan Khan M.B.B.S.[4]
Overview
Screening for tuberculosis is generally done by using a mantoux tuberculin skin test, also known as a tuberculin skin test or a PPD. The test involves injecting a small amount of a purified protein derivative of the tuberculosis bacterium intradermally and watching for a reaction in the following days.
Screening
Mantoux Tuberculin Skin Test
The Mantoux tuberculin skin test (TST) is the standard method of determining whether a person is infected with Mycobacterium tuberculosis. Reliable administration and reading of the TST require a standardization of procedures, training, supervision, and practice. The TST is performed by injecting 0.1 ml of tuberculin purified protein derivative (PPD) into the inner surface of the forearm. The injection should be made with a tuberculin syringe, with the needle bevel facing upward. The TST is an intradermal injection. When placed correctly, the injection should produce a pale elevation of the skin (a wheal) 6 to 10 mm in diameter.
The skin test reaction should be read between 48 and 72 hours after administration. A patient who does not return within 72 hours will need to be rescheduled for another skin test.
The reaction should be measured in millimeters of the induration (palpable, raised, hardened area, or swelling). The reader should not measure erythema (redness). The diameter of the indurated area should be measured across the forearm (perpendicular to the long axis).
TST is contraindicated only for persons who have had a severe reaction (e.g., necrosis, blistering, anaphylactic shock, or ulcerations) to a previous TST. It is not contraindicated for any other persons, including infants, children, pregnant women, persons who are HIV-infected, or persons who have been vaccinated with BCG.
In some persons who are infected with M. tuberculosis, the ability to react to tuberculin may wane over time. When given a TST years after infection, these persons may have a false-negative reaction. However, the TST may stimulate the immune system, causing a positive, or boosted reaction to subsequent tests. Giving a second TST after an initial negative TST reaction is called two-step testing.
Two-step testing is useful for the initial skin testing of adults who are going to be retested periodically, such as health care workers or nursing home residents. This two-step approach can reduce the likelihood that a boosted reaction to a subsequent TST will be misinterpreted as a recent infection.
Classification of Tuberculin Reaction
Skin test interpretation depends on two factors:
- Measurement in millimeters of the induration.
- Person’s risk of being infected with TB and of progression to disease if infected.
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| Tuberculin Reaction | Considered a Positive Result in: |
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| ≥ 5 mm |
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| ≥ 10 mm |
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| ≥ 15 mm |
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| Table adapted from CDC[1] | |
| False-Positive Reactions | False-Negative Reactions |
|---|---|
Some persons may react to the TST even though they are not infected with M. tuberculosis. The causes of these false-positive reactions may include, but are not limited to, the following:
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Some persons may not react to the TST even though they are infected with M. tuberculosis. The reasons for these false-negative reactions may include, but are not limited to, the following:
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| Table adapted from CDC[1] | |
Recommendations for Human Immunodeficiency Virus (HIV) Screening in Tuberculosis Clinics Adapted from CDC[2]
- CDC recommends HIV screening for all TB patients after the patient is notified that testing will be performed unless the patient declines (i.e., opt-out screening). This includes persons with TB disease and persons with latent TB infection.
- Routine HIV testing is also recommended for persons suspected of having TB disease, persons diagnosed with latent TB infection, and contacts to TB patients.
- Prevention counseling and separate written consent for HIV testing should no longer be required.
- These recommendations are aimed at eliminating missed opportunities for HIV screening and reducing significant barriers to HIV testing in health care settings by:
- Opt-out screening is defined as performing HIV testing after notifying the patient that the test will be performed, and although the patient may decline or defer testing, it is strongly recommended. Assent is inferred unless the patient declines to test.
Quantiferon Gold testing
- The early detection of infection with Mycobacterium tuberculosis (Mtb) remains a complicated issue pertaining to the control and prevention of TB.[3]
- For many years, the tuberculin skin test (TST) was the test most commonly used for the diagnosis of TB infection due to its low cost and convenience in most countries.[4]
- PPD testing has several disadvantages, including poor specificity in people who received the Bacille Calmette-Guerin (BCG) vaccination.[5]
- In the last decade, interferon gamma release assays (IGRAs) have been introduced to aid in the detection of Latent Tuberculosis.[6]
- Interferon-gamma release assays (IGRAs) are immunodiagnostics tools in which interferon-gamma (IFN-γ) released by T-cells in response to Mycobacterium tuberculosis-specific antigen is measured.[7]
- During the past decade, two commercial in vitro IGRAs, including the QuantiFERON-TB Gold In-Tube (QFT-GIT) test and T-SPOT.TB have been introduced for the early detection of M. tuberculosis infection.[7]
- Innterferon Gold testing include proteins that are almost exclusively present in mycobacterium tuberculosis than those in the purified derivative (PPD) and that are encoded by genes that are not found in mycobacterium bovis, BCG, or most environmental mycobacteria.[8]
- The QuantiFERON-TB Gold In-Tube test (QFT-GIT) assay measures the IFN-γ concentration in whole blood after stimulation by specific tuberculosis antigens.[8]
- The Quantiferon Gold test has been largely employed to evaluate the diagnosis of M. tuberculosis infection in developed countries.[6]
- whether the QFT-GIT will be useful in monitoring the responses to anti-tuberculosis treatment is unclear.[9]
| Category | 2005 Recommendation | 2019 Recommendation |
|---|---|---|
| Baseline (preplacement) screening and testing | TB screening of all HCP, including a symptom evaluation and test (IGRA or TST) for those without documented prior TB disease or LTBI. | TB screening of all HCP, including a symptom evaluation and test (IGRA or TST) for those without documented prior TB disease or LTBI (unchanged); individual TB risk assessment (new). |
| Postexposure screening and testing | Symptom evaluation for all HCP when exposure is recognized. For HCP with a baseline negative TB test and no prior TB disease or LTBI, perform a test (IGRA or TST) when the exposure is identified. If that test is negative, do another test 8–10 weeks after the last exposure. | Symptom evaluation for all HCP when exposure is recognized. For HCP with a baseline negative TB test and no prior TB disease or LTBI, perform a test (IGRA or TST) when the exposure is identified. If that test is negative, do another test 8–10 weeks after the last exposure (unchanged). |
| Serial screening and testing for HCP without LTBI | According to health care facility and setting risk assessment. Not recommended for HCP working in low-risk health care settings. Recommended for HCP working in medium-risk health care settings and settings with potential ongoing transmission. | Not routinely recommended (new); can consider for selected HCP groups (unchanged); recommend annual TB education for all HCP (unchanged), including information about TB exposure risks for all HCP (new emphasis). |
| Evaluation and treatment of positive test results | Referral to determine whether LTBI treatment is indicated. | Treatment is encouraged for all HCP with untreated LTBI, unless medically contraindicated (new). |
| Abbreviations: IGRA = interferon-gamma release assay; LTBI = latent tuberculosis infection; TST = tuberculin skin test.
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References
- ↑ 1.0 1.1 "CDC Tuberculin Skin Testing".
- ↑ "CDC Recommendations for Human Immunodeficiency Virus (HIV) Screening in Tuberculosis (TB) Clinics".
- ↑ "WHO | Global tuberculosis report 2018, SYSTEM DO NOT MOVE OR EDIT".
- ↑ Houben RM, Dodd PJ (October 2016). "The Global Burden of Latent Tuberculosis Infection: A Re-estimation Using Mathematical Modelling". PLoS Med. 13 (10): e1002152. doi:10.1371/journal.pmed.1002152. PMC 5079585. PMID 27780211.
- ↑ Detjen AK, Keil T, Roll S, Hauer B, Mauch H, Wahn U, Magdorf K (August 2007). "Interferon-gamma release assays improve the diagnosis of tuberculosis and nontuberculous mycobacterial disease in children in a country with a low incidence of tuberculosis". Clin. Infect. Dis. 45 (3): 322–8. doi:10.1086/519266. PMID 17599309.
- ↑ 6.0 6.1 Lu P, Chen X, Zhu LM, Yang HT (June 2016). "Interferon-Gamma Release Assays for the Diagnosis of Tuberculosis: A Systematic Review and Meta-analysis". Lung. 194 (3): 447–58. doi:10.1007/s00408-016-9872-5. PMID 27039307.
- ↑ 7.0 7.1 Lalvani A (June 2007). "Diagnosing tuberculosis infection in the 21st century: new tools to tackle an old enemy". Chest. 131 (6): 1898–906. doi:10.1378/chest.06-2471. PMID 17565023.
- ↑ 8.0 8.1 Dilektasli AG, Erdem E, Durukan E, Eyüboğlu FÖ (November 2010). "Is the T-cell-based interferon-gamma releasing assay feasible for diagnosis of latent tuberculosis infection in an intermediate tuberculosis-burden country?". Jpn. J. Infect. Dis. 63 (6): 433–6. PMID 21099095.
- ↑ Dheda K, Pooran A, Pai M, Miller RF, Lesley K, Booth HL, Scott GM, Akbar AN, Zumla A, Rook GA (August 2007). "Interpretation of Mycobacterium tuberculosis antigen-specific IFN-gamma release assays (T-SPOT.TB) and factors that may modulate test results". J. Infect. 55 (2): 169–73. doi:10.1016/j.jinf.2007.02.005. PMID 17448540.