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Phthisiology
Diagnosis of TB
Lecture 2
Diagnosis of TB-disease. Clinical
signs. Investigations.
Diagnosis of TB Disease
1.
2.
3.
4.
5.
6.
7.
8.
Clinical signs
Medical History
Physical Examination
Test for TB Infection
X-ray examination
Microscopy of sputum smear for TB bacilli
Bacteriologic investigations
Bronchoscopy
Symptoms of Pulmonary TB
• Cough lasting 3 or more weeks
• Coughing up sputum or blood (Hemoptysis)
• Chest pain
• Breathlessness
•
General Symptoms of TB Disease
• Weakness
• Fatigue
• Malaise
• rapid fatigability
• bad appetite
• weight loss
• fever
• increased perspiration
• decreased capacity for work
• Night sweats
Symptoms of Extrapulmonary TB
Disease
•
Symptoms of extrapulmonary TB disease depend on
part of body that is affected
• For example:
– TB disease in spine may cause back pain
– TB disease in kidneys may cause blood in urine
Medical History
• Information about
close contact with
infectious case of TB
helps to clear
diagnosis
Close contacts
• Close contacts are people who spend time with someone who
has infectious TB disease
• May include:
– Family members
– Coworkers
– Friends
• On average, 20 – 30% of close contacts become infected with
TB
Risk to be infected
family
Friends,
relatives
Random
contacts
Physical Examination
• A physical examination cannot confirm or rule
out TB disease, but can provide valuable
information
• Physical changes depends on extension of the
disease and its complications
• Physical signs of parenchyma consolidation,
lung contraction, pneumothorax and pleural
exudates could be present
Physical Examination include
• General exam - weight loss, pale and moist
skin and pale visible mucosa, nail clubbing
(drumstick fingers and watch-glass nails),
patient's hand may be cyanotic
• Palpation ()
• Percussion
• Auscultation
Hematological Study
• Intoxication and hypoxia cause changes in the
blood of patient
• leucocytosis up to 10-14 x 10^9 / L
• ↑ ESR (erythrocyte sedimentation rate)
Test for TB Infection
• Types of tests for
diagnosing TB infection
– TST
– IGRAs
• QFT-G
• QFT-GIT
• T-SPOT
Mantoux Tuberculin Skin Test
•TST is administered by
injection
•Tuberculin is made from
proteins derived from
inactive tubercle bacilli
• Most people who have
TB infection will have a
reaction at injection
site
Mantoux Tuberculin Skin Test
• Forearm should be
examined within 48 - 72
hours
• Reaction is an area of
induration (swelling)
around injection site
-Induration is measured
in millimeters
-Erythema (redness) is
not measured
Mantoux Tuberculin Skin Test
Interpreting the Reaction - 1
• Interpretation of TST reaction depends on size
of induration and person’s risk factors for TB
Mantoux Tuberculin Skin Test
Interpreting the Reaction - 2
• Absence of changes is considered negative
• Redness only or induration 2-4 mm is
considered doubtful
• Induration of > 5 mm is considered positive
• Induration of > 17 mm in child is considered
hyperergic
• Induration of > 21 mm in adult is considered
hyperergic
Mantoux Tuberculin Skin Test
Interpreting the Reaction - 3
• Vesicle, bulla, necrosis and lymphangitis are
considered hyperergic
Mantoux Tuberculin Skin Test and
BCG Vaccine
• People who have been vaccinated with BCG may
have a false-positive TST reaction
• Individuals should always be further evaluated if they
have a positive TST reaction
Mantoux Tuberculin Skin Test
Any patient with symptoms of TB disease
should be evaluated for TB disease, regardless of
his or her skin test reaction.
Conditions, which suppress
Mantoux test result
• HIV-infection
• Malnutrition
• Severe bacterial infections, including
tuberculosis by itself
• Viral infections: measles, chicken pot,
glandular fever
• Cancer
• Immunosuppressive drugs: steroids
Interferon-Gamma
Release Assays (IGRAs)
• QuantiFERON®-TB Gold (QFT-G)
(2005)
• QuantiFERON®-TB Gold In-Tube
(QFT-GIT)
– Approved 10/2007
• T-Spot®.TB test (T-SPOT)
– Type of ELISpot assay
– Approved 7/2008
• Guidelines for IGRAs are under
development
TB test Materials
Image Credit: U.S.
Food and Drug
Administration
(FDA), 2009
QFT-G and QFT-GIT
• IGRAs measure a person’s immune reactivity to M.
tuberculosis. White blood cells from most persons
that have been infected with M. tuberculosis will
release interferon-gamma (IFN-g) when mixed with
antigens (substances that can produce an immune
response) derived from M. tuberculosis.
• To conduct the tests, fresh blood samples are mixed
with antigens and controls. The antigens, testing
methods, and interpretation criteria for IGRAs differ
IGRAs
• Interferon-Gamma Release Assays (IGRAs) - Blood Tests for TB Infection
• What are they?
• Interferon-Gamma Release Assays (IGRAs) are whole-blood tests that can
aid in diagnosing Mycobacterium tuberculosis infection. They do not help
differentiate latent tuberculosis infection (LTBI) from tuberculosis disease.
Two IGRAs that have been approved by the U.S. Food and Drug
Administration (FDA) are commercially available in the U.S:
• QuantiFERON®-TB Gold In-Tube test (QFT-GIT);
• T-SPOT®.TB test (T-Spot)
• What are the advantages of IGRAs?
• Requires a single patient visit to conduct the test.
• Results can be available within 24 hours.
• Does not boost responses measured by subsequent tests.
• Prior BCG (bacille Calmette-Guérin) vaccination does not cause a falsepositive IGRA test result.
QFT-G and QFT-GIT
Conducting the Test
• Follow manufacturer’s instructions
• Confirm arrangements for delivery and testing of
blood within 12 hours of collection
• Draw sample of blood into tube with heparin
• Schedule appointment for patient to receive test
results
• If needed, medical evaluation and treatment for
LTBI or TB disease
QFT-G and QFT-GIT
How it Works
• Blood samples are mixed with antigens and
incubated for 16 - 24 hours
• If infected with M. tuberculosis, blood cells
will recognize antigens and release interferon
gamma (IFN-γ) in response
• Results are based on the amount of IFN-γ
released in response to antigens and control
substances
QFT-G and QFT-GIT
Interpreting Results
• Test results are based
on IFN-γ
concentrations
• Laboratories can use
software provided by
manufacturer to
calculate results
• Results are sent to
requesting clinician
QFT-G and QFT-GIT
Report of Results
• Positive - M. tuberculosis infection likely
• Negative - M. tuberculosis infection
unlikely, but cannot be excluded especially
if: Patient has TB signs and symptoms
or patient has a high risk for
developing TB disease once infected
with M. tuberculosis
T-SPOT
• Type of ELISpot assay
• Interferon gamma is presented as spots from T
cells sensitized to M. tuberculosis
• Results are interpreted by subtracting the spot
count of the control from the spot count of
the sample
Differences in Currently Available IGRAs
Initial Process
QFT-GIT
T-Spot
Process whole blood within 16 Process peripheral blood
hours
mononuclear cells (PBMCs)
within 8 hours, or if T-Cell
Xtend® is used, within 30 hours
M. tuberculosis Antigen
Single mixture of synthetic
peptides representing ESAT-6,
CFP-10 & TB7.7.
Separate mixtures of synthetic
peptides representing ESAT-6 &
CFP-10
Measurement
IFN-g concentration
Number of IFN-g producing cells
(spots)
Possible Results
Positive, negative,
indeterminate
Positive, negative,
indeterminate, borderline
T-SPOT results
Chest X-Ray
• Help rule out possibility of pulmonary TB
disease in a person who has positive TST or
QFT-G result and no symptoms of TB
• Check for lung abnormalities in people who
have symptoms of TB disease
Classical patterns of pulmonary
tuberculosis
•
•
•
•
Upper lobe infiltration
Bilateral infiltration
Cavitation
Pulmonary fibrosis and shrinkage
Other shadows, which may be due
to tuberculosis, are:
• Oval or round shadows (tuberculoma)
• Hilar and mediastinal lymphadenopathy
• Diffused small nodular shadow
The indications for tomography
• Diffused shadow
• Cavitation suspect
• Hilar
Tuberculoma. Longitudinal
tomography:
Chest x-ray. Tuberculosis infiltrate
with cavitation in upper right lung
Chest x-ray.
• Chest x-rays cannot confirm TB disease
– Other diseases can cause lung abnormalities
– Only bacteriologic culture can prove patient has
TB disease
– Chest x-ray may appear unusual or even appear
normal for persons living with HIV
CT (computer tomography)
Representative chest radiography and CT images. (A) A pretransplant CXR
appeared to be normal, but (B) pretransplant chest CT scanning revealed a TBsuggestive lesion (an uncalcified nodule). (C) Active TB developed 6 months
after LT in the same location.
Precaution
• It is a major error to diagnose tuberculosis on
x-ray and fail to examine the sputum
Bacteriologic Examination
• TB bacteriologic examination is done in a laboratory
that specifically deals with M. tuberculosis and other
mycobacteria
– Clinical specimens (e.g., sputum and urine) are
examined and cultured in laboratory
Bacteriologic Examination
• Bacteriologic examination has 5 parts
– Specimen collection
– Examination of acid-fast bacilli (AFB) smears
– Direct identification of specimen (nucleic acid
amplification)
– Specimen culturing and identification
– Drug susceptibility testing
Specimen Collection
• For pulmonary TB, specimens
can be collected by:
– Sputum sample
– Induced sputum sample
– Bronchoscopy
– Gastric washing
Sputum Sample Specimen
Collection
• Easiest and least expensive method is to have patient
cough into sterile container
• HCWs should coach and instruct patient
• Should have at least 2 sputum specimens examined
– Collected in 8-24 hour intervals
– At least one early morning specimen
Induced Sputum Collection
• Induced sputum collection should be used if
patient cannot cough up sputum on their own
• Patient inhales saline mist, causing deep
coughing
• Specimen often clear and watery, should be
labeled “induced specimen”
Extrapulmonary TB
• Specimens other than sputum may be obtained
• Depends on part of body affected
• For example:
– Urine samples for TB disease of kidneys
– Fluid samples from area around spine for TB
meningitis
Examination of AFB Smears
• Specimens are
smeared onto glass
slide and stained
• AFB are mycobacteria
that remain stained
after being washed in
acid solution
Examination of AFB Smears
• Number of AFB on smear are counted
• According to number of AFB seen, smears are
classified as 4+, 3+, 2+, or 1+
– For example, 4+ smear has 10 times as many AFB
than 3+ smear
• If very few AFB are seen, the smear is classified by
the actual number of AFB seen
Examination of AFB Smears
•
•
•
•
•
•
Classification of Smear Result
4+ Strongly positive - Probably very infectious
3+ Strongly positive - Probably very infectious
2+ Moderately positive - Probably infectious
1+ Moderately positive - Probably infectious
Actual number of AFB seen (no plus sign) Weakly positive - Probably infectious
• No AFB seen–Negative - May not be infectious
Culturing and Identifying Specimen
• Step 1: Detect growth of mycobacteria
- Solid media: 3 - 10 weeks
- Liquid media: 4 - 14 days
• Step 2: Identify organism that has grown
– Nucleic acid probes: 2 - 4 hours
– Biochemical tests: 6 - 12 weeks
Culturing and Identifying Specimen
• Positive culture: M. tuberculosis identified in
patient’s culture
– Called M. tuberculosis isolate
– Confirms diagnosis of TB disease
Culturing and Identifying Specimen
• Negative culture: M. tuberculosis NOT identified in
patient’s culture
– Does not rule out TB disease
– Some patients with negative cultures are
diagnosed with TB based on signs and symptoms
Culturing and Identifying Specimen
• Bacteriological examinations are important for
assessing infectiousness and response to
treatment
• Specimens should be obtained monthly until 2
consecutive cultures are negative
• Culture conversion is the most important
objective measure of response to treatment
Drug Susceptibility Testing
• Conducted when patient is first found to have
positive culture for TB
• Determines which drugs kill tubercle bacilli
• Tubercle bacilli killed by a particular drug are
susceptible to that drug
• Tubercle bacilli that grow in presence of a
particular drug are resistant to that drug
Drug Susceptibility Testing
Drug susceptibility
testing on solid
media
Types of Drug-Resistant TB
• Mono-resistant - Resistant to any one TB
treatment drug
• Poly-resistant - Resistant to at least any two
TB drugs (but not both isoniazid and
rifampicin)
Types of Drug-Resistant TB
• Multidrug- resistant (MDR TB) - Resistant to
at least isoniazid and rifampicin, the two best
first-line TB treatment drugs
• Extensively drug-resistant TB (XDR TB) Resistant to isoniazid and rifampicin, PLUS
resistant to any fluoroquinolons AND at least 1
of the 3 injectable second-line drugs (e.g.,
amicacin, kanamycin, or capreomycin)
(XDR TB Arial)
Bronchoscopy
• Procedure: instrument
is passed through nose
or mouth into lung for
direct visualization of
tracheobronchial tree
and to obtain
pulmonary secretions
or lung tissue
Indications for bronchoscopy in TB
patient
• Hilar shadowing
• Unclear etiology of lung hemorrhage
• Presence of TB bacilli in the sputum without xray confirmation of lung abnormality
• Suspected TB bronchitis
• Bronchial obstruction
• Atelectasis