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Diagnosis of Pulmonary Tuberculosis Presenter: 4A Ri 范綱志 Sep. 29,2008 Why diagnosis important? Diagnosis of tuberculosis in most cases clinical diagnosis based upon the clinical presentation (hx & PE) In 15-20% of p’t with suspected TB lab confirmation never obtained

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diagnosis of pulmonary tuberculosis

Diagnosis of Pulmonary Tuberculosis

Presenter: 4A Ri范綱志

Sep. 29,2008

why diagnosis important
Why diagnosis important?
  • Diagnosis of tuberculosis in most cases
    • clinical diagnosis based upon the clinical presentation (hx & PE)
  • In 15-20% of p’t with suspected TB
    • lab confirmation never obtained
  • Early diagnosis and initiation of effective therapy
    • reducing morbidity and mortality from TB
    • minimize the spread of infection
outline
Outline
  • Screening for prior infection
    • Tuberculin skin test
  • Diagnosis of pulmonary TB
    • Medical history
    • Physical examination
    • Chest radiograph
    • Bacteriologic exam
screening for prior infection
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 induration by palpation
mantoux tuberculin test
Mantoux Tuberculin Test
  • Preferred method of testing for TB infection 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
mantoux test
Mantoux test
  • Inject intradermally 0.1 mlof 5TU PPD tuberculin
  • Produce wheal 6 mm to 10mm in diameter
  • Represent DTH (delayed type hypersensitivity)
reading of mantoux test
Reading of Mantoux test
  • Read reaction 48-72 hours after injection
  • Measure only induration
  • Record reaction in mm
classifying the tuberculin reaction
Classifying the tuberculin reaction
  • >5 mm is classified as positive in
    • HIV-positive persons
    • Recent contacts of TB case
    • Persons with fibrotic changes on CXR consistent with old healed TB
    • Patients with organ transplants and other immunosuppressed patients
classifying the tuberculin reaction10
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 clinical conditions that place them at high risk
    • Children <4 years, or children and adolescents exposed to adults in high-risk categories
classifying the tuberculin reaction11
Classifying the tuberculin reaction
  • >15 mm is classified as positive in
    • Persons with no known risk factors for TB
factors may affect tst
Factors may affect TST
  • False negative
    • Faulty application
    • Anergy
    • Acute TB (2-10 wks to convert)
    • Very young age (< 6 months old)
    • Live-virus vaccination
    • Overwhelming TB disease
  • False positive
    • BCG vaccination (usually <10mm by adulthood)
    • Nontuberculous mycobacteria infection
boosting
Boosting
  • Some people with LTBI may have negative skin test reaction when tested years after infection
  • Initial skin test may stimulate (boost) ability to react to tuberculin
  • Positive reactions to subsequent tests may be misinterpreted as a new infection
two step testing
Two-Step Testing
  • Use two-step testing for initial skin testing of adults who will be retested within 1-3 weeks
    • 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
screening for prior infection15
Screening for prior infection
  • 台灣早年結核病盛行率高
  • 50年前20歲以上成人
    • 80% TST 為陽性
  • 年齡越大,TST對結核病的診斷幫助越小
diagnosis of disease
Diagnosis of disease
  • Medical history
  • Physical examination
  • Chest radiograph
  • Bacteriologic exam
    • AFS
    • Culture
medical history19
Medical History
  • Symptoms of disease
  • History of TB exposure, infection, or disease
  • Past TB treatment
  • Demographic risk factors for TB
  • Medical conditions that increase risk for TB disease
medical history20
Medical History
  • High prevalence population
    • More likely to be exposed to and infected with bacillus
      • Immigrant from high prevalence area
      • Resident or worker in jail
      • Long term care facility
      • Close contact to p’t with active TB
medical history21
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
physical examination23
Physical Examination
  • Productive, prolonged cough
    • duration of ~3 weeks‏
  • Chest pain
  • Hemoptysis
  • Fever/Chills
  • Night sweats
  • Appetite loss
  • Weight loss
  • Easily fatigued
chest radiography25
Chest radiography
  • Classical radiograph appearance
    • Infiltration
    • Cavitation
    • Fibrosis with traction
    • Enlargement of hilar and mediastinal lymph node
  • In reactivaiton TB
    • Classically fibrocavitary apical disease
  • Primary TB
    • Middle or lower lobe consolidation
chest radiography26
Chest radiography
  • Abnormalities often seen in apical or posterior segments of upper lobe or superior segments of lower lobe
  • May have unusual appearance inHIV-positive persons
  • Cannot confirm diagnosis of TB!!

cavity in patient‘s RUL

classic" for adult-type, reactivation tuberculosis

classic adult tb cxr
Classic adult TB CXR
  • PA view
    • diffuse parenchymal disease with multiple cavities and bulla formation on the left
    • Sputum smear was positive for AFB
chest radiography28
Chest radiography
  • No chest X-ray pattern is absolutely typical of TB
  • 10-15% of culture-positive TB patients not diagnosed by X-ray
  • 40% of patients diagnosed as having TB on the basis of x-ray alone do not have active TB
slide29

X-ray-based evaluation causes over-diagnosis of TB

Over-

diagnosis

NTI, Ind J Tuberc, 1974

specimen collection
Specimen Collection
  • Obtain 3 sputum specimens for smearexamination and culture
  • Persons unable to cough up sputum
    • inducesputum
    • bronchoscopy
    • gastric aspiration
  • Follow infection control precautions during specimen collection
three specimens
Three Specimens
  • Three specimens optimal
    • Spot specimen on first visit; sputum container given to patient
    • Early morning collection by patient on next day
    • Spot specimen during second visit
number of sputum samples required
Number of sputum samples required
  • overall diagnostic yield for sputum examination related to
    • the quantity of sputum (at least 5 mL)
    • the quality of sputum
    • multiple samples obtained at different times to the laboratory for processing
      • 3 samples obtained at least eight hours apart with at least one sample obtained in the early morning
number of sputum samples required35
Number of sputum samples required
  • several studies have suggested that only two samples may be sufficient to capture the majority of cases:
    • Retrospective study
      • Nelson, SM, Deike, MA, Cartwright, CP. Value of examining multiple sputum specimens in the diagnosis of pulmonary tuberculosis. J Clin Microbiol 1998; 36:467.
        • overall, 92 percent of cases would have been detected 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 additional value
smear examination
Smear Examination
  • Strongly consider TB in patients with smears containing acid-fast bacilli (AFB)‏
  • Results should be available within 24 hours of specimen collection
  • Presumptive diagnosis of TB
  • Not specific for M. tuberculosis
afb smear
AFB Smear
  • Sensitivity: 40-70%
  • Specificity: 90%
afb smear38
AFB smear

AFB (shown in red) are tubercle bacilli

reporting on afb microscopy

Number of bacilli seen

Result reported

None per 100 oil immersion fields

Negative

1-9 per 100 oil immersion fields

Scanty, report

exact number

10-99 per 100 oil immersion fields

1+

1-10 per oil immersion field

2+

> 10 per oil immersion field

3+

Reporting on AFBMicroscopy
slide40

HIV

Negative

70

60

Early HIV

50

40

Late HIV

30

20

10

0

Proportion of patients with pulmonary

TB who have positive AFB smears

AFB positivity in

TB patients

open tuberculosis
Open tuberculosis
  • A tuberculous ulceration or other form of tuberculosis in which tubercle bacilli are present in the excretions or secretions.
  • Pulmonary tuberculosis, especially with cavitation.
  • 開放性結核就是在病人咳出的痰液中有結核桿菌的存在
slide42

Cultures

  • Gold standard for TB diagnosis
  • Use to confirm diagnosis of TB
  • Culture all specimens, even if smear negative
  • Results in 4 to 14 days when liquid medium
  • systems used

Colonies of M. tuberculosis growing on media

cultures
Cultures
  • Sensitivity: 80-85%
  • Specificity: 98%
  • Times needed:
    • Solid medium
      • 4-8 wks
    • Liquid medium
      • 2 wks
afb smear vs cultures
AFB smear vs. Cultures
  • AFB smear
    • 可檢測到每ml標本有5000-10000隻細菌
    • 染色陰性並不能排除結核病
    • Rapid diagnosis
  • Cultures
    • 每ml標本只需有10-100隻細菌便可檢測到
    • More sensitive
    • Allows drug susceptivity test
slide45

Microscopy is more objective

and reliable than X-ray

Inter-observer

agreement

slide47

Cough 3 weeks

If 1 positive,

X-ray and

evaluation

AFB X 3

If 2/3 positive:

Anti-TB Rx

Ifnegative:

Broad-spectrum antibiotic 10-14 days

If symptoms persist, repeat AFB smears, X-ray

If consistent with TB

Anti-TB Treatment

Diagnosis of Pulmonary TB

take home message
Take Home Message
  • 診斷結核病必須綜合
    • 臨床表現
      • Non-specific symptoms
    • 放射學變化
      • Often over diagnosis
    • 實驗室細菌學診斷
      • AFB smear
        • Rapid diagnosis, presumptive diagnosis
      • Culture
        • Gold standard, more sensitive
  • 只要強烈懷疑TB可先開始進行抗結核治療
source
Source
  • UpToDate, Diagnosis of pulmonary tuberculosis, 2008, John Bernardo,MD
  • 行政院衛生署疾病管制局,結核病診治指引, Taiwan Guidelines on TB Diagnosis & Treatment, Edition 3, 主編陸坤泰