Diagnostic Tests for Tuberculosis
Tuberculosis: Diagnostic Tests
The list of diagnostic tests
mentioned in various sources as
used in the diagnosis of Tuberculosis
includes:
- Chest x-ray
- TB skin test - also called Mantoux test or purified protein derivative (PPD) test
- Sputum test for tuberculosis
- Lung fluid tests for tuberculosis
- Biopsy
- Lymph node biopsy
Tuberculosis Tests: Book Excerpts
Home Diagnostic Testing
These home medical tests may be relevant to Tuberculosis:
- Lung & Respiratory Health Tests:
- Bladder & Urinary Health: Home Testing:
- Kidney Health: Home Testing:
Tuberculosis Diagnosis: Book Excerpts
Tests and diagnosis discussion for Tuberculosis:
Tuberculosis, NIAID Fact Sheet: NIAID (Excerpt)
The tuberculin skin test, also known as the Mantoux test, can
identify most people infected with tubercle bacilli six to eight
weeks after initial exposure. A substance called purified protein
derivative (PPD) is injected under the skin of the forearm and
examined 48 to 72 hours later. If a red welt forms around the
injection site, the person may have been infected with M.
tuberculosis, but doesn't necessarily have active disease.
Most people with previous exposure to TB will test positive on the
tuberculin test, as will some people exposed to related
mycobacteria. An important exception is people with severely
weakened immune systems, such as those with HIV.
If a person has a significant reaction to the tuberculin skin
test, additional methods can determine if the individual has
active TB. This is sometimes difficult because TB can mimic other
diseases, such as pneumonia, lung abscesses, tumors, and fungal
infections, or occur along with them. In making a diagnosis,
doctors rely on symptoms and other physical signs, a person's
history of exposure to TB, and x-rays that may show evidence of TB
infection, usually in the form of cavities or lesions in the
lungs.
The physician also will take sputum and other samples, because
a positive bacteriologic culture of M. tuberculosis is
essential to confirm the diagnosis and determine which drugs will
work against the strain of TB the patient carries. Because M.
tuberculosis grows very slowly, the laboratory diagnosis
requires approximately four weeks. An additional two to three
weeks usually are needed to determine the drug susceptibility of
the organism, making treatment decisions
difficult.
Advances in Diagnosis
Recently, researchers supported by the National Institute of
Allergy and Infectious Diseases (NIAID) as well as other
investigators developed tests that use nucleic acid amplification
to speed the diagnosis of TB from four weeks to two days. Another
test in development uses luminescent chemicals from the firefly to
determine, in 24 to 48 hours, which drugs can kill the TB strain a
patient carries.
Treatment of Active Disease
The death rate for untreated TB patients is between 40 and 60
percent. With appropriate antibiotics, however, people with
drug-susceptible cases of TB can be cured more than 90 percent of
the time.
Successful management of TB depends on close cooperation
between the patient and physicians and other health care workers.
Patient education is essential, and many doctors opt for
supervised, directly observed therapy (DOT). Treatment usually
combines the drugs isoniazid (INH) and rifampin, which are given
for at least six months, and pyrazinamide and ethambutol (or
streptomycin), which are used only in the first two months of
treatment. This treatment is referred to as short-course
chemotherapy.
Therapy for MDR-TB
Treatment for MDR-TB often requires the use of a second line of
TB drugs, all of which can produce serious side effects. Therapy
for 18 months to two years may be necessary, and patients should
receive at least three drugs to which the bacteria are
susceptible.
Prevention
TB is largely a preventable disease. In the United States,
prevention has focused on identifying infected individuals early —
especially those who run the highest risk of developing active
disease — and treating them with drugs in a program of directly
observed therapy.
INH prevents the disease in most people in close contact with
infected people or who are infected with the tubercle bacilli but
who do not have active TB. The drug is given daily for six to 12
months and strict patient compliance in taking medication is
essential to prevent drug-resistant strains from emerging. Adverse
reactions to INH are rare, although a small percentage of
patients, especially those older than 35, suffer INH-related
hepatitis. Rifampin for one year is recommended for close contacts
of patients with INH-resistant TB organisms.
In the United States, people with any of the following risk
factors should be considered for preventive therapy, regardless of
age, if they have not been previously treated for TB:
- Close contacts of people with newly diagnosed infectious TB;
(In addition, children and adolescents who react negatively to
the PPD test, but who have been in close contact with infectious
people within the past three months, should be considered for
preventive therapy. Therapy should continue until a second skin
test is done 12 weeks after their first contact with an
infectious person.)
- People with positive tuberculin skin tests and abnormal
chest x-rays compatible with inactive TB (lesions caused by
prior disease);
- People whose skin test results have recently converted from
negative to positive;
- People with positive skin test reactions who also have
special medical conditions known to increase the risk of TB
(e.g., HIV infection, diabetes mellitus) or who are on
corticosteroid therapy;
- HIV-positive people or those suspected to be HIV-infected
who now have, or had at any time in the past, positive skin test
reactions, but who do not have active infection; and
- Injection drug users who have positive skin test reactions.
In addition, people younger than 35 in the following groups
should be considered for preventive therapy if they have positive
skin test reactions:
- Foreign-born people from countries where TB is common;
- People in medically underserved, low-income groups,
especially African Americans, Hispanics, and Native Americans;
and
- Residents of long-term care facilities such as prisons,
nursing homes, and mental institutions.
Health care workers in frequent contact with TB patients or
involved with high-risk procedures such as those that induce
coughing should have a skin test every six months.
Hospitals and clinics caring for high-risk populations can take
precautions to prevent the spread of TB. All patients should be
taught to cover their mouths and noses when coughing or sneezing.
Ultraviolet light can be used to sterilize the air, and negative
pressure rooms and special filters are available, as are special
respirators and masks, that filter out the droplet nuclei. Until
they are no longer infectious, hospitalized TB patients should be
isolated in rooms with controlled ventilation and air
flow.
More Effective Vaccines are
Needed
In those parts of the world where the disease is common, a
vaccine composed of live, attenuated (weakened) mycobacteria from
cows (M. bovis, called bacillus Calmette-Guerin [BCG]) is
given to infants as part of the immunization program recommended
by the World Health Organization (WHO). In infants, BCG prevents
the spread of M. tuberculosis within the body, but does not
prevent initial infection.
In adults, the effectiveness of BCG has varied widely in
large-scale studies. In addition, positive skin test reactions
occur in people who have received BCG vaccine, thus limiting the
effectiveness of the PPD skin test to identify new infections. As
a result, BCG is not recommended for general use in the United
States. Because of BCG's limitations, more effective vaccines are
needed.
TB and HIV Infection
WHO estimates that 4.4 million people worldwide are coinfected
with TB and HIV. By the year 2000, TB will claim 1 million lives
annually among the HIV-infected, WHO projects, making TB the
leading cause of death in HIV-infected individuals. In the United
States, an estimated 100,000 HIV-infected people also carry M.
tuberculosis, according to CDC.
TB frequently occurs early in the course of HIV infection,
often months to years before other opportunistic infections such
as Pneumocystis carinii pneumonia. TB may be the first
indication that a person is HIV-infected, and often occurs in
areas outside the lungs, particularly in the later stages of HIV
disease.
In the United States, people coinfected with TB and HIV develop
active TB at a rate of about 8 percent each year. By
comparison, otherwise healthy individuals infected with M.
tuberculosis have a 10 percent lifetime risk of
developing active TB. People with HIV also are at greater risk of
having a new infection progress directly to active disease.
MDR-TB in people coinfected with HIV appears to have a more
rapid and deadly disease course than seen in patients with MDR-TB
who are otherwise healthy.
Diagnosing TB in HIV-infected people is often difficult. These
patients frequently have conditions that produce symptoms similar
to those of TB, and may not react to the standard tuberculin skin
test because their immune systems are suppressed. Although
investigators have hypothesized that a two-stage TB skin test
might be more reliable than a single-stage test in HIV-infected
individuals, a recently completed NIAID study found this not to be
the case.
X-rays, sputum smears, and physical exams may also fail to
provide an indication of TB infection in HIV-infected individuals.
As a consequence, doctors must often decide to begin anti-TB
therapy in HIV-infected people suspected of having active TB while
waiting for the results of cultures of sputum or other specimens.
NIAID Research Agenda for
Tuberculosis
NIAID, the lead institute for TB research at the National
Institutes of Health, supports more than 100 research projects
related to TB. In fiscal year 1999, NIAID will devote an estimated
$40 million to TB research.
NIAID has a comprehensive TB research agenda that supports the
following:
- Studies of the epidemiology and natural history of TB.
- Basic research into the biology of TB and the host immune
response to M. tuberculosis.
- The development of new tools to diagnose TB.
- The development of new drugs or new ways to deliver standard
drugs.
- Clinical trials of anti-TB therapies.
- The development of new vaccines to prevent TB.
- Training to increase the number of TB researchers.
- New ways to educate health care workers and the public about
TB prevention.
This multi-disciplinary program draws on the Institute's
expertise in immunology and microbiology, as well as its
capabilities in drug and vaccine development honed as part of the
research effort in AIDS and other infectious
diseases.
(Source: excerpt from
Tuberculosis, NIAID Fact Sheet: NIAID)
Tuberculosis, NIAID Fact Sheet: NIAID (Excerpt)
Recently, researchers supported by the National Institute of
Allergy and Infectious Diseases (NIAID) as well as other
investigators developed tests that use nucleic acid amplification
to speed the diagnosis of TB from four weeks to two days. Another
test in development uses luminescent chemicals from the firefly to
determine, in 24 to 48 hours, which drugs can kill the TB strain a
patient carries. (Source: excerpt from Tuberculosis, NIAID Fact Sheet: NIAID)
Tuberculosis: NWHIC (Excerpt)
A TB skin test is the only way to find out if you have TB infection.
You can get a skin test at the health department or at your doctor's
office. (Source: excerpt from Tuberculosis: NWHIC)
Diagnosis of Tuberculosis: medical news summaries:
The following medical news items
are relevant to diagnosis of Tuberculosis:
Diagnostic Tests for Tuberculosis: Online Medical Books
16 MEDICAL BOOKS ONLINE!
Review excerpts from medical books online, free, without registration,
for more information about the diagnostic tests for Tuberculosis.
Do not routinely test children for tuberculosis (TB) exposure:
Testing
(Avoiding Common Pediatric Errors)
The tuberculin skin test is one method to determine if a person has TB.
Althoughthereareseveralskintestsavailable,thepreferredmethodisknown
as the Mantoux test, which involves intradermal administration of 0.1 mL
of 5 tuberculin units (TU) as a partial protein derivative (PPD), usually at
the flexor surface (dorsal or volar) of the forearm. The test should be read 48
to 72 hours after administration, and the transverse diameter of induration
should be measured in millimeters.
» READ BOOK EXCERPT ONLINE »
Source: Avoiding Common Pediatric Errors, 2008
Pediatric Tuberculosis:
Use of Anergy Testing
(Pediatric Infectious Disease)
Up to 20% of patients with active tuberculosis have a negative TST at initial
presentation. In the 1970s, the idea of evaluating negative tuberculin tests
results by assessing reactions to a panel of unrelated antigens (such as
candida or tetanus) was proposed. This concept of
anergy testingbecame a routine adjunct to tuberculin skin testing. Despite its widespread use,
the validity of this approach has never been proved. The ability to respond to
other antigens has been shown not to improve the reliability of a negative TST
test. Studies have also shown that the results of anergy testing do not predict
the risk for progression to active disease in either HIV-negative or
HIV-positive patients. For this reason, routine anergy testing, used as a
validation to tuberculin skin testing, is not recommended by most infectious
disease specialists.
Although Bacille Calmette-Guérin (BCG) vaccine is not routinely given in the United States, the pediatrician
will need to interpret TST in children who have received this vaccine. After
BCG vaccination, distinguishing a positive reaction secondary to latent
infection from reactivity to BCG is difficult. One study found that only 8% of
persons who had received BCG vaccine at birth had a positive TST 15 years
later. It is for this reason that the American Academy of Pediatrics recommends
the same criteria for TST interpretation in patients who have received BCG.
» READ BOOK EXCERPT ONLINE »
Source: Pediatric Infectious Disease, 2004
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