tuberculin testing
TRANSCRIPT
DR.T.V.RAO MD 1
Dr.T.V.Rao MD
TUBERCULIN SKIN TESTING
MANTOUX TUBERCULIN SKIN TEST
TUBERCULOSIS: PRIMARY INFECTION
• 95% of cases begin with pulmonary focus
• usually a SINGLE focus• hypersensitivity
develops 2 to 6 weeks• until then, focus may
grow larger• hypersensitivity brings
caseation
PRIMARY INFECTION: LYMPHO-HEMATOGENOUS SPREAD
• 8-14 weeks after onset of TB• usually occult• Mantoux positive during this
phase• body wide seeding occurs during
this phase• bone, kidney, meninges etc.• 3% of children with nl CXR’s
develop calcifications in lung apices (SIMON FOCI)
DR.T.V.RAO MD 4
USUAL PROGRESSION OF PRIMARY INFECTION
infection
Lympho-hematogenous spread
healed PRIMARY infection
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PROGRESSIVE PRIMARY DISEASE
pleural effusion
cavitation
lymph node involvement
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TUBERCULIN SKIN TESTING
• The Mantoux tuberculin skin test (TST) is the standard method of determining whether a person is infected with Mycobacterium tuberculosis. Reliable administration and reading of the TST requires standardization of procedures, training, supervision, and practice.
The issues:
• Applying the tuberculin skin test
• Reading the test
• Interpreting the test – including in children
• Management of positive TST
DIAGNOSIS OF LATENT TB WITH THE TUBERCULIN SKIN TEST
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DR.T.V.RAO MD 8
INDICATIONS FOR SKIN TEST SCREENING• Persons with signs and/or symptoms suggestive of tuberculosis disease
• Recent contacts of persons known or suspected to have tuberculosis
• Persons with undiagnosed upper lobe fibrotic lesions
• Persons infected with HIV
• Alcoholics and intravenous drug abusers
• Persons with medical conditions known to increase the risk of disesase if infection has occurred:
• silicosis, gastrectomy, jejunoileal bypasss, significant weight loss below IBW, chronic renal failure, diabetes mellitus, high dose corticosteroid treatment or other immunosuppressive therapy, leukemia, lymphoma, malignancy
• Groups at high risk of infection:
• Latin America, Oceana, medically underserved populations, residents of long term care facilities
• Groups that would pose a significant risk to others if diseased: employees of health care facilities, schools, child care facilities
ATS/CDC
DR.T.V.RAO MD 9
THE TB SKIN TEST: MATERIALS• OLD TUBERCULIN
• culture of TB bacillus in glycol peptone broth
• TB “tine” test
• PURIFIED PROTEIN DERIVATIVE (PPD)• TB bacillus grown in Long’s media, filtered after heating
• adopted by WHO as standard in 1950
• PPD-S 1952
• dose = 5 IU
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• Intra-dermal
• quality control important
• trained practioner necessary
• Delayed hypersensitivity
• cell mediated
• 48-72 hours• False negative
• immuno-compromized conditions
• measles/measles immunizations
• Nonspecific reactions
• increase >10 IU
• cross reactions, atypical MB
THE TB (MANTOUX) SKIN TEST
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APPLYING THE TUBERCULIN SKIN TEST
Courtesy of Dr. Marc Steben
DR.T.V.RAO MD 12
APPLYING THE TUBERCULIN SKIN TEST
DR.T.V.RAO MD 13
REACTION TO THE TUBERCULIN SKIN TEST
Courtesy of Dr. Marc Steben
DR.T.V.RAO MD 14
READING THE TUBERCULIN SKIN TEST
Courtesy of Dr. Marc Steben
• Read 2-3 days after placing the test
• Feel for induration
• Color change without induration is not included in the measurement
• Use a ruler or calipers
• Have someone else check if unsure
• Always document the exact size (mm) – not just “positive” or “negative”
READING THE TUBERCULIN SKIN TEST
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DR.T.V.RAO MD 16
• A positive TB skin test only tells that a person has been infected with TB bacteria. It does not tell whether the person has latent TB infection (LTBI) or has progressed to TB disease.
A POSITIVE SKIN TEST ONLY INDICATES
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• The reaction should be measured in millimetres of the induration (palpable, raised, hardened area or swelling). The reader should not measure erythema (redness). The diameter of the indurated area should be measured across the forearm (perpendicular to the long axis).
READING THE SKIN TESTING IN TUBERCULOSIS
PRIMARY INFECTION: LYMPHO-HEMATOGENOUS SPREAD
• 8-14 weeks after onset of TB• usually occult• Mantoux positive during this
phase
• body wide seeding occurs during this phase• bone, kidney, meninges etc.• 3% of children with nl CXR’s
develop calcifications in lung apices (SIMON FOCI)
• Read 2-3 days after placing the test
• Feel for induration
• Color change without induration is not included in the measurement
• Use a ruler or calipers
• Have someone else check if unsure
• Always document the exact size (mm) – not just “positive” or “negative”
READING THE TUBERCULIN SKIN TEST
DR.T.V.RAO MD 19
DR.T.V.RAO MD 20
FACTORS CAUSING DECREASED ABILITY TO RESPOND TO TUBERCULIN
• Factors related to the person being tested• Infections
• Viral (measles, mumps, chickenpox)
• Bacterial (typhoid fever, brucelosis, typhus, pertussis, overwhelming TB,
• Fungal (South American blastomycosis)
• Live virus vaccinations (MMR)
• Metabolic derangements (chronic renal failure)
• Nutritional factors (severe protein depletion)
• Diseases affecting lymphid organs (Hodgkin’s lymphoma, chronic lymphocytic leukemia, sarcoidosis)
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FACTORS CAUSING DECREASED ABILITY TO RESPOND TO TUBERCULIN (CONTD)
• Drugs (corticosteroids, other immunosuppressive agents)
• Age (newborn, elderly)
• Recent overwhelming infection with M. tuberculosis
• Stress (surgery, burns, mental illness, graft versus host reactions)
• Factors related to the tuberculin used
• Factors related to the method of administration
• Factors related to reading the test and recording results
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MILIARY DISEASEGENERALIZED HEMATOGENOUS TUBERCULOSIS
• generalized dissemination through bloodstream
• caseous focus ruptures into blood vessel
• growth of tubercle within the blood vessel
• may be acute, occult or chronic
• uniformly fatal if not treated
• rare
• usually occurs in the first 4 months after primary infection
MILIARY Disease• millet seed appearance
on X-ray
• Mantoux positive?• Most children still have
active primary complex when miliary disease strikes
• most develop meningitis
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Evaluate for active TB• Re-check
symptoms and exam – cough, fever, weight loss, enlarged lymph nodes, dyspnea
• Chest X-ray, if possible
EVALUATION OF A PATIENT WITH POSITIVE TST
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• Programme Created by Dr.T.V.Rao MD for Medical and Health Care Workers in
the Developing World • Email