Phthisiology Diagnosis of TB. Diagnosis of TB-disease. Clinical signs. Investigations. Lecture 2.

Phthisiology

Diagnosis of TB

Diagnosis of TB-disease. Clinical signs. Investigations.

Lecture 2

Diagnosis of TB Disease

1. Clinical signs2. Medical History3. Physical Examination4. Test for TB Infection5. X-ray examination6. Microscopy of sputum smear for TB bacilli7. Bacteriologic investigations8. 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 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

Symptoms of Extrapulmonary TB Disease

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 infectedRisk to be infected

familyfamily

Friends, Friends, relativesrelatives

Random Random contactscontacts

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 diseaseshould 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 MaterialsImage 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 false-

positive IGRA test result.

QFT-G and QFT-GITConducting 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 QFT-GIT T-Spot

Initial Process Process whole blood within 16 hours

Process peripheral blood 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 TB-suggestive 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 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”

Induced Sputum Collection

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

• 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 x-

ray confirmation of lung abnormality• Suspected TB bronchitis• Bronchial obstruction• Atelectasis