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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
  • 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
  • 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

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



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


1-9 per 100 oil immersion fields

Scanty, report

exact number

10-99 per 100 oil immersion fields


1-10 per oil immersion field


> 10 per oil immersion field


Reporting on AFBMicroscopy





Early HIV



Late HIV





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


  • 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

  • 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

Microscopy is more objective

and reliable than X-ray




Cough 3 weeks

If 1 positive,

X-ray and



If 2/3 positive:

Anti-TB Rx


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
  • 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