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Diagnosis of Pulmonary
Tuberculosis
Presenter: 4A Ri
Sep. 29,2008
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Why diagnosis important?
Diagnosis of tuberculosis in most cases clinical diagnosis based upon the clinical presentation
(hx & PE)
In 15-20% of pt with suspected TB lab confirmation never obtained
Early diagnosis and initiation of effectivetherapy
reducing morbidity and mortality from TB
minimize the spread of infection
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Outline
Screening for prior infection
Tuberculin skin test
Diagnosis of pulmonary TB Medical history
Physical examination
Chest radiograph
Bacteriologic exam
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Screening for prior infectionTuberculin skin test
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Screening for prior infection
Whom to screen High prevalence and high risk population
(HIV)
How to screen Mantoux tuberculin test (ie, purified protein
derivative or PPD, tuberculin skin test)
How to interpret Determine maximum diameter of indurationby palpation
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Mantoux Tuberculin Test
Preferred method of testing for TBinfection in adults and children
Tuberculin skin testing useful for Examining person who is not ill but may be
infected
Determining how many people in group are
infected
Examining person who has symptoms of TB
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Mantoux test
Inject intradermally0.1 ml of 5TU PPDtuberculin
Produce wheal 6 mmto 10 mm in diameter
Represent DTH
(delayed typehypersensitivity)
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Reading ofMantoux test
Read reaction 48-72hours after injection
Measure onlyinduration
Record reaction inmm
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Classifying the tuberculin reaction
>5 mm is classified as positive in
HIV-positive persons
Recent contacts of TB case Persons with fibroticchanges on CXR
consistent with old healed TB
Patients with organ transplants and other
immunosuppressed patients
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Classifying the tuberculin reaction
>10 mm is classified as positive in Recent arrivals from high-prevalence
countries
Injection drug users Residents and employees of high-risk settings
Mycobacteriology laboratory personnel
Persons with clinicalconditions that placethem at high risk
Children
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Classifying the tuberculin reaction
>15 mm is classified as positive in
Persons with no known risk factors for TB
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Factors may affect TST
False negative Faulty application
Anergy
Acute TB (2-10 wks to convert) Very youngage (< 6 months old)
Live-virus vaccination
Overwhelming TB disease
False positive BCG vaccination (usually
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Boosting
Some people with LTBI may havenegative skin test reaction when tested
years after infection Initial skin test may stimulate (boost)ability to react to tuberculin
Positive reactions to subsequent tests maybe misinterpreted as a new infection
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Two-Step Testing
Use two-step testing for initial skin testingof adults who will be retested within 1-3weeks
If first test (+), consider the person infected
If first test (-), give second test 1-3 weeks later
If second test (+), consider person infected
If second test (-), consider person uninfected
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Screening for prior infection
5020 80% TST
,TST
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Diagnosis of Pulmonary TB
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Diagnosis of disease
Medical history
Physical examination Chest radiograph
Bacteriologic exam
AFS Culture
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Medical History
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Medical History
Symptoms of disease
History of TB exposure, infection, or
disease Past TB treatment
Demographic risk factors for TB
Medicalconditions that increase risk forTB disease
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Medical History
High prevalence population
More likely to be exposed to and infected withbacillus
Immigrant from high prevalence area
Resident or worker in jail
Long term care facility
Close contact to pt with active TB
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Medical History
High risk population More likely to progress from infection to active TB
HIV (+) or other immunodeficiency
CRF DM
IVDA
Alcoholics
Malnourished
Malignancy
Gastrectomy
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Ph
ysical Examination
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Physical Examination
Productive, prolonged cough duration of ~3 weeks
Chest pain
Hemoptysis Fever/Chills
Night sweats
Appetite loss
Weight loss
Easily fatigued
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Chest radiograp
hy
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Chest radiography
Classical radiograph appearance Infiltration
Cavitation
Fibrosis with traction Enlargement of hilar and mediastinallymph node
In reactivaiton TB
Classically fibrocavitary apical disease
Primary TB Middle or lower lobe consolidation
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Chest radiography
Abnormalities oftenseen in apical orposterior segments of
upper lobe orsuperior segments oflower lobe
May have unusualappearance in HIV-positive persons
Cannot confirmdiagnosis of TB!!
cavity in patients RULclassic" for adult-type, reactivation tuberculosis
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Classic adult TB CXR
PA view
diffuse parenchymaldisease with multiplecavities and bullaformation on the left
Sputum smear waspositive for AFB
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Chest radiography
No chest X-ray pattern is absolutelytypical of TB
10-15% of culture-positive TB patients notdiagnosed by X-ray
40% of patients diagnosed as having TBon the basis of x-ray alone do not haveactive TB
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0
20
40
60
80
100
Diagnosed by X-
ray alone
Actual cases
X
-ray-based evaluation causesover-diagnosis of TB
NTI, Ind J Tuberc, 1974
Over-
diagnosis
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Bacteriologic Exam
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Specimen Collection
Obtain 3 sputum specimens for smearexamination and culture
Persons unable to cough up sputum induce sputum bronchoscopy
gastricaspiration
Follow infection control precautionsduring specimen collection
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Three Specimens
Three specimens optimal
Spot specimen on first visit; sputum containergiven to patient
Early morningcollection by patient on nextday
Spot specimen during second visit
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Three sputum smears are optimal
81%
93%
100%
0%
50%
100%
First Second ThirdCumulativePositivity
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Number of sputum samples required
overall diagnostic yield for sputumexamination related to
the quantity of sputum (at least 5 mL)
the quality of sputum
multiple samples obtained at different timesto the laboratory for processing
3 samples obtained at least eight hours apart withat least one sample obtained in the early morning
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Number of sputum samples required
several studies have suggested that only twosamples may be sufficient to capture themajority of cases:
R
etrospective study Nelson, SM, Deike,MA, Cartwright, CP. Value of examining multiple sputumspecimens in the diagnosis of pulmonary tuberculosis. J ClinMicrobiol 1998; 36:467.
overall, 92 percent of cases would have beendetected with two specimens
Craft, DW, Jones, MC, Blanchet, CN, et al. Value of examining three acid-fact bacillus
sputum smears for the removal of patients suspected of having tuberculosis from the"airborn precautions"category. J Clin Microbiol 2000; 38:4285.
a third sputum smear was of no additionalvalue
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Smear Examination
Strongly consider TB in patients withsmears containingacid-fast bacilli (AFB)
Results should be available within 24hours of specimen collection
Presumptive diagnosis of TB
Not specific for M. tuberculosis
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AFB Smear
Sensitivity: 40-70%
Specificity: 90%
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Reporting on AFBMicroscopy
Number ofbacilli seen Result reported
None per 100 oil immersion fields Negative
1-9 per 100 oil immersion fields Scanty, reportexact number
10-99 per 100 oil imm
ersion fields 1+
1-10 per oil immersion field 2+
> 10 per oil immersion field 3+
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Proportion of patients with pulmonary
TB who have positive AFB smears
0
10
20
30
40
50
60
70 HIVNegative
Early HIV
Late HIV
AFB positivity in
TB patients
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Open tuberculosis
A tuberculous ulceration or other form of
tuberculosis in wh
ich
tubercle bacilli arepresent in the excretions or secretions.
Pulmonary tuberculosis, especially withcavitation.
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Cultures
Colonies of
M. tuberculosisgrowing on media
Gold standard for TB diagnosisUse to confirm diagnosis of TBCulture all specimens, even if smear negativeResults in 4 to 14 days when liquid mediumsystems used
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Cultures
Sensitivity: 80-85%
Specificity: 98%
Times needed: Solid medium
4-8 wks
Liquid medium
2 wks
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AFB smear vs. Cultures
AFB smear
ml5000-10000
Rapid diagnosis
Cultures
ml10-100
More sensitive
Allows drug susceptivity test
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98%
70%
0
20
40
60
80
100
AFB Microscopy X-ray
Microscopy is more objective
and reliable than X-ray
Inter-observer
agreement
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50%
98%
0
20
40
60
80
100
AFB Microscopy X-ray
M
icroscopy is a more specific test th
anX-ray for TB diagnosis
Specificity
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Diagnosis of Pulmonary TBCough 3 weeks
AFB X 3
Broad-spectrum antibiotic 10-14 days
If symptoms persist, repeat AFB smears, X-ray
If consistent with TB
Anti-TB Treatment
If 1 positive,
X-ray andevaluation
If 2/3 positive:Anti-TB Rx
Ifnegative:
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Diagnosis of pulmonary TB
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Recommended DiagnosticApproach
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Take HomeMessage
Non-specific symptoms
Often over diagnosis
AFB smear
Rapid diagnosis, presumptive diagnosis
Culture
Gold standard, more sensitive
TB
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Source
UpToDate, Diagnosis of pulmonarytuberculosis, 2008, John Bernardo,MD
,
,Taiwan Guidelines on TB Diagnosis &Treatment, Edition 3,
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Th
anks for your attention!
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