Synonym/Acronym
TST, TB tine test, PPD, Mantoux skin test, QuantiFERON-TB Gold blood test (QFT-G), QuantiFERON-TB Gold In-Tube test (QFT-GIT), T-SPOT.TB test (T-SPOT).
Rationale
To evaluate for current or past tuberculin infection or exposure.
Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.
Normal Findings
Method: Intradermal skin test, culture/enzyme-linked immunosorbent assay (ELISA) blood test for QuantiFERON assays, enzyme-linked ImmunoSpot (ELISPOT) for T-SPOT.TB test. Negative.
Specific infectious organisms are required to be reported to local, state, and national departments of health. Lists of specific organisms may vary among facilities. State health departments provide information regarding reportable diseases, which can be accessed at each state health department Web site. The Centers for Disease Control and Prevention (CDC) provides information regarding national notifiable diseases at https://ndc.services.cdc.gov/search-results-year.
Study type: Blood collected in a green-top [LiHep] tube [QuantiFERON-TB Gold and T-SPOT.TB blood tests], whole blood collected in each of three special [nil, antigen, and mitogen] specimen containers [QuantiFERON-TB Gold In-Tube test]; related body system: Immune and Respiratory systems.
Routine screening for tuberculosis (TB) has not been needed for some time because, until recently, the disease had largely been eradicated. In 2019, the CDC updated its TB recommendations for health-care personnel:
- Baseline screening with individual risk assessment and symptom evaluation for all personnel
- No further routine testing at any interval after baseline in the absence of known exposure or infection
- Annual symptom screening and recommendations for treatment as needed (and unless contraindicated) for personnel with untreated latent TB infection
- Testing with an interferon-gamma release assay (IGRA) or a T-spot test (TST) for personnel without documented prior TB infection or latent TB infection and who have had a known exposure to TB
- Symptom evaluation, chest x-ray, and treatment (as appropriate) for personnel with a newly positive test result
- Annual TB education for all health-care personnel
Recommendations for the general public regarding the timing of initial screening and subsequent recommendations may vary according to state laws, practitioners’ guidelines, and specific circumstances (foreign adoptions or immigration from areas where TB is endemic or in high-risk environments such as health-care or congregated settings). Children and adults are screened on the basis of a risk assessment. For example, the American Academy of Pediatrics recommends identifying individuals at highest risk by means of a questionnaire before testing, and adults who either work or reside in a high-risk environment are required to submit to annual Mantoux testing or chest x-ray (for individuals with a previously positive Mantoux test or individuals from other countries who have received the Bacillus Calmette–Guérin [BCG] vaccine).
Blood and skin tests are approved as indirect tests for Mycobacterium tuberculosis, and the CDC recommends their use in conjunction with risk assessment, chest x-ray, and other appropriate medical and diagnostic evaluations.
Skin Tests for TB
Tuberculin skin tests are done to determine past or present exposure to TB. The multipuncture or tine test is no longer used as a screening technique and has been largely replaced by the more definitive Mantoux test using Aplisol or Tubersol, purified protein derivatives (PPDs) of the mycobacterial cell wall, administered by intradermal injection. The Mantoux test is the test of choice in symptomatic patients. It is also used in some settings as a screening test. A negative result is judged if there is no sign of redness or induration at the site of the injection or if the zone of redness and induration is less than 5 mm in diameter. TB skin tests are classified in three categories depending on the measured diameter (in millimeters) of the induration and the person’s risk of being infected or of progressing to developing TB if infected.
- A positive result evidenced by an area of erythema and induration at the injection site greater than 5 mm is considered to be positive in persons infected with HIV, persons who have been in recent contact with an individual who has TB, persons with chest x-ray findings consistent with a previous TB infection, persons who have received transplanted organs, or persons who are immunosuppressed from other causes.
- A positive result evidenced by an area of erythema and induration at the injection site greater than 10 mm is considered to be positive in persons who have immigrated or are foreign adoptees from a country with a high prevalence of TB within the past 5 yr; persons who misuse drugs by injection; persons who work in mycobacteriology laboratories; persons who work or live in highly congregated settings; children less than 4 yr of age; any person with a clinical condition whose immune system is immature, suppressed, or otherwise compromised; and any younger person (infant through adolescent) who has been exposed to adults in a high-risk group.
- A positive result evidenced by an area of erythema and induration at the injection site greater than 15 mm is considered to be positive in any person.
A positive result does not distinguish between active and dormant infection. A positive response to the Mantoux test is followed up with chest radiography and bacteriological sputum testing to confirm diagnosis.
Blood Tests for TB
The QuantiFERON-TB Gold (QFT-G), QuantiFERON-TB Gold In-Tube (QFT-GIT), and T-SPOT TB interferon–gamma release blood tests, also known as interferon–gamma release assays (IGRAs), are approved by the U.S. Food and Drug Administration for all applications in which the TB skin test is used.
The blood tests are procedures in which T lymphocytes from the patient, either in whole blood or harvested from whole blood, are incubated with a reagent cocktail of peptides that simulate two or three proteins made only by M. tuberculosis. These proteins are not found in the blood of previously vaccinated individuals or individuals who do not have TB. The blood test offers the advantage of eliminating many of the false reactions encountered with skin testing, only a single patient visit is required, and results can be available within 24 hr. Results obtained by the QFT-G test are not affected by BCG vaccination.
Molecular technologies are another approach to testing various specimen types; there are now numerous applications in the areas of pathogen identification (e.g., TB), disease identification (e.g., oncology), and treatment development. Next-generation sequencing (NGS) is a category of molecular testing used to sequence DNA fragments. NGS technology is capable of sequencing DNA fragments from pathogenic organisms across a range in size from small sequences (single-nucleotide polymorphisms) to large sequences (thousands or billions).
The indications for NGS have expanded significantly, and it is now an important tool in the diagnosis/identification of pathogenic organisms. NGS also provides a means and/or the potential to perform prognostic epidemiological studies, lineage tracing (cell lines), discovery of genetic variants with drug resistance mutations, development of individualized therapeutic regimens, and development of preventive measures (e.g., vaccines). Multiplex assays are another type of molecular testing designed to simultaneously sequence DNA fragments from multiple pathogens to help identify mixed populations of infectious agents.
Factors That May Alter the Results of the Study
General
- Each of the blood and skin tests evaluate different facets of the immune response and use different methodologies and reagents; interpretations may not be interchangeable.
Skin Test
- Drugs such as immunosuppressive drugs or steroids can alter results.
- Diseases such as hematological cancers or sarcoidosis can alter results.
- Recent or present bacterial, fungal, or viral infections may affect results. False-positive results may be caused by the presence of non-TB mycobacteria or by serial testing.
- False-negative results can occur if sensitized T cells are temporarily decreased. False-negative results also can occur in the presence of bacterial infections, immunological deficiencies, immunosuppressive agents, live-virus vaccinations (e.g., measles, mumps, varicella, rubella), malnutrition, old age, overwhelming TB, kidney disease, and active viral infections (e.g., chickenpox, measles, mumps).
- Improper storage of the tuberculin solution (e.g., with respect to temperature, exposure to light, and stability on opening) may affect the results.
- Improper technique when performing the intradermal injection (e.g., injecting into subcutaneous tissue) may cause false-negative results.
- Incorrect amount or dilution of antigen injected or delayed injection after drawing the antigen up into the syringe may affect the results.
- Incorrect reading of the measurement of response or timing of the reading may interfere with results.
- It is not known whether the test has teratogenic effects or reproductive implications; the test should be administered to pregnant women only when clearly indicated.
- The test should not be administered to a patient with a previously positive tuberculin skin test because of the danger of severe reaction, including vesiculation, ulceration, and necrosis.
- The test does not distinguish between current and past infection.
Blood Test
- The performance of these blood tests has not been evaluated in large studies with patients who have impaired or altered immune function, have or are highly likely to develop TB, are younger than age 17 yr, are pregnant, or have diseases other than TB. These individuals are either immunosuppressed, immunocompromised, or have immature immune function and may not produce sufficient numbers of T lymphocytes for accurate results. The testing laboratory should be consulted for interpretation of results or limitations for use with patients in these categories.
- False-negative results are possible due to exposure or infection prior to development of detectable immune response.
- False-positive results are possible due to some cross-reactivity to some strains of environmental mycobacteria.
- False-negative results are possible due to exposure or infection prior to development of detectable immune response.
Potential Nursing Problems: Assessment & Nursing Diagnosis
| Problems | Signs and Symptoms |
|---|
| Breathing (related to productive cough, fatigue, inflammation) | Tachypnea, dyspnea, orthopnea, change in the rate and depth of respirations, retractions, nasal flare, use of accessory muscles | | Infection (related to exposure to M. tuberculosis) | Productive cough of bloody sputum, fever with temperature spikes, positive acid-fast bacilli (AFB) smear, fatigue, night sweats, weight loss, chills, lack of appetite | | Nutrition(insufficient—related to poor appetite secondary to M. tuberculosis infection) | Unintended weight loss; pale, dry skin; dry mucous membranes; documented inadequate caloric intake; subcutaneous tissue loss; hair pulls out easily; self-report of no appetite |
|
Before the Study: Planning and Implementation
Teaching the Patient What to Expect
- Discuss how this test can assess for a tuberculin infection or exposure.
- Explain that a blood sample is needed for the QuantiFERON-TB Gold and T-SPOT.TB tests.
Skin Test
- Before beginning the test, ensure there is no current active TB and there is no history of a previously positive skin test.
- Explain that the procedure takes approximately 5 min.
- The test should not be administered if there is a skin rash or other eruptions at the test site.
- Explain that a moderate amount of pain may be experienced when the intradermal injection is performed.
- Emphasize the importance of not scratching or disturbing the area after the injection and before the reading.
- Ensure that epinephrine hydrochloride solution (1:1,000) is available in the event of anaphylaxis.
- The skin site should be cleansed on the lower anterior forearm with alcohol swabs and allowed to air-dry.
Mantoux (Intradermal) Test
- A PPD or old tuberculin in a tuberculin syringe is prepared with a short, 26-gauge needle attached.
- The appropriate dilution and amount are prepared by qualified and trained personnel.
- The most commonly used intermediate strength is 5 tuberculin units in 0.1 mL or a first strength usually used for children (1 tuberculin unit in 0.1 mL).
- Appropriately trained personnel inject the preparation intradermally at the prepared site as soon as it is drawn up into the syringe.
- When properly injected, a bleb or wheal 6 to 10 mm in diameter is formed within the layers of the skin.
- The site is recorded and the patient reminded to return in 48 to 72 hr to have the test read.
- At the time of the reading, a plastic ruler is used to measure the diameter of the largest indurated area.
- The area is palpated for thickening of the tissue; a positive result is indicated by a reaction of 5 mm or more with erythema and edema.
- To ensure accuracy, the reading is performed by specially trained personnel in a room with sufficient light.
Potential Nursing Actions
- Obtain a history of TB or TB exposure, signs and symptoms indicating possible TB, and other skin tests or vaccinations and sensitivities.
After the Study: Implementation & Evaluation Potential Nursing Actions
Treatment Considerations
- Explain the clinical implications of the test results.
- Discuss the implications of abnormal test results on the patient’s lifestyle.
- Be supportive of perceived loss of independence and fear of shortened life expectancy.
- Inform the patient that the effects from a positive response at the skin testing site can remain for 1 wk.
- Explain that a positive result may place one at risk for infection related to impaired primary defenses, impaired gas exchange related to decrease in effective lung surface, and intolerance to activity related to an imbalance between oxygen supply and demand.
Breathing
- Assess and trend respiratory rate and effort.
- Monitor for retractions, nasal flare, and use of accessory muscles.
- Evaluate cough effectiveness and auscultate lungs for adventitious breath sounds.
- Monitor pulse oximetry and administer ordered oxygen therapy; prepare for possible mechanical intubation.
- Encourage oral fluids, cough and deep breathing, and pace activities.
Infection
- Send ordered sputum specimen for culture.
- Consider inducing a sputum specimen if the patient is unable to provide one through cough.
- Place the patient in isolation (negative airflow) until AFB results are obtained.
- Administer prescribed medications.
- Instruct the patient regarding the proper way to cover the mouth when coughing or sneezing and to frequently wash hands, especially after coming into contact with contaminated sputum.
- Explain the importance of visitors wearing masks.
- Explain that all confirmed TB cases are reported to the department of health.
Nutritional Considerations
- Encourage a high-calorie, high-protein diet and an increased intake of oral fluids.
- Perform a daily weight and obtain an accurate nutritional history.
- Assess attitude toward eating; promote a dietary consult to evaluate current eating habits and best method of nutritional supplementation.
- Monitor nutritional laboratory values (albumin), assess swallowing ability, and encourage cultural home foods.
- Provide a pleasant environment for eating; alter food seasoning to enhance flavor; provide parenteral or enteral nutrition as prescribed.
Clinical Judgement
- Consider how to emphasize the importance of self-isolation toward prevention of TB community spread.
Follow-Up and Desired Outcomes
- Acknowledges the risk of transmission and proper prophylaxis, and agrees to adhere to the treatment regimen.
- Aware that positive findings must be reported to local health department officials, who will question the patient regarding other persons who may have been exposed through contact. Educate the patient regarding access to counseling services.
- Understands that those who receive skin testing must return and have the test results read within the specified time frame of 48 to 72 hr after injection.