Purpose of TST

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Purpose of TST

• Purpose of TST is to detect LTBI
• TST is useful when
• Examining close contacts to active TB cases
• Target testing those at high risk for TB
  infection
• Examining person with active TB symptoms

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Purpose of TST (2)

• Facts about tuberculin
• Protein derived from dead tubercle bacilli
• Administered intradermally
• most people with TB infection have reaction to
  TST (swelling, not redness)
• TST is not vaccine will not give person TB
  infection or disease
• TST is safe and reliable during pregnancy
• Available brands Tubersol? and Aplisol?
  (equally effective)

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Types of Tests

• Mantoux TST
• Used in U.S. since 1930s
• Most widely used and most accurate
• "TST technicians" are trained and certified to
  use Mantoux method

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Types of Tests (2)

• QuantiFeron-TB
• Relatively new, not yet widely available
• Blood test
• Fast (results in 1 day)
• Convenient (1 patient visit)
• Possible increased accuracy
• Not yet recommended by CDC for
• TB suspects
• contacts

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Types of Tests (3)

• Not yet recommended by CDC for (cont)
• lt 17 years old
• pregnant women
• HIV-infected persons
• Multiple puncture test (MPT) ("tine" test)
• Outdated, unreliable, should no longer be used
• Involves puncturing skin with 3-tine device
  pre-coated with tuberculin

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Mantoux Test

• First step administering TST
• 0.1 ml of 5 tuberculin units of liquid tuberculin
  injected intradermally on inner aspect of forearm
• PPD
• tuberculin solution also known as "purified
  protein derivative" (PPD)
• TST sometimes referred to as PPD skin test

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Mantoux Test (2)

• Second step measuring reaction
• Timeframe
• 4872 hours after injection examine patients
  arm for reaction
• over 72 hours re-administer TST
• Reaction induration around injection site
  (recorded in mm)
• Patients should never "read" their own reactions
  must be read by trained health worker

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Mantoux Test (3)

• Third step interpreting/classifying reaction
• By law, TST technicians may not be certified to
  interpret, and may not interpret, results
• "Positive reactions" occur in many, but not all,
  patients infected with M. tb

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Mantoux Test (4)

• Supplies used in Mantoux method
• Tuberculin
• Single-dose disposable tuberculin needle and
  syringe
• Gauze pads or cotton balls
• Alcohol swabs
• Puncture-resistant sharps disposal container

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Mantoux Test (5)

• Supplies used in Mantoux method (cont)
• 6. Patient and provider forms patient
  education materials appointment cards
• 7. Pen
• 8. Ruler with millimeters
• 9. Insulated cooler (for field testing)
• Gloves

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Mantoux Test (6)

• Storage and handling of tuberculin
• Multidose vials contain 10 or 50 tests
• Refrigerate at 35-46?F (2-8?C) (in the field,
  store in coolers with ice packs)
• Store and transport in dark
• When opening new vial
• check for appropriate unit strength
• date and initial vial

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Mantoux Test (7)

• Storage and handling of tuberculin (cont)
• Find expiration date (discard if expired or open
  for gt 30 days)
• Draw tuberculin into needle just prior to
  injection

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Universal Precautions

• Universal precautions
• Describes approach to infection control for
  health workers developed by CDC
• Treats all blood and body fluids as potentially
  hazardous
• Reduces health worker's risk of exposure to
  dangerous blood-borne pathogens

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Universal Precautions (2)

• Universal precaution measures
• Handle needles or sharp objects with extreme care
• Always dispose of needles and sharp items in
  accessible, puncture-resistant container
• Ensure that sharps containers are closable,
  leakproof, and labeled
• Wash hands and skin immediately and thoroughly if
  contaminated with blood or other bodily fluids

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Universal Precautions (3)

• Universal precaution measures (cont)
• Treat all biomedical waste as potentially
  hazardous (dispose of used bandages, dressings,
  and gloves in biohazard bags)
• Wear protective eyewear to minimize direct
  contact with body fluids
• Wash hands after giving care
• Wear gloves if possible exposure to blood or
  other bodily fluids exists
• Wash hands immediately after removing gloves

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Interpretation of TST

• What makes TST reaction positive or negative?
• Two factors
• size of induration
• persons risk factors
• Persons with more serious risk factors are
  considered positive with smaller-sized reactions

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Interpretation of TST (2)

• Classifying TST reactions
• gt 5 mm classified as positive in
• HIV-positive persons
• recent contacts of active pulmonary TB case
• persons with chest radiographs that suggest old
  healed TB disease
• patients with organ transplants and other
  immunosuppressed patients
• gt 10 mm classified as positive in
• all others not listed above

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Interpretation of TST (3)

• False-positive and false-negative reactions
• Mantoux TST is not perfect
• Person not infected with M. tb may display
  "false-positive" due to
• infection with nontuberculous mycobacteria
• history of BCG vaccination

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Interpretation of TST (4)

• Person infected with M. tb may show
  "false-negative" due to
• too recent TB infection
• TB infection too long ago
• anergy
• very young age (lt 6 months)
• recent live-virus vaccine
• errors (in storing or administering tuberculin
  solution, or reading TST)
• Never rule out infection or active disease if TST
  reaction is negative

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Two-step Testing

• Person with LTBI for many years sometimes may not
  produce reaction to baseline TST
• Over time, immune system has lost some
  sensitivity to tuberculin
• First TST "boosts" immune systems ability to
  react
• If re-tested 1-3 weeks later, positive reaction
  can occur
• This reaction should not be confused for new
  infection

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Two-step Testing (2)

• Two-step testing recommended for adults given
  periodic TSTs (e.g., healthcare staff in
  high-risk settings)
• Upon hire, two-step testing ensures that true
  baseline is obtained without "boosting"
• If person has positive reaction at a later time,
  it is due to recent transmission rather than
  boosting

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BCG

• BCG
• TB vaccination
• Administered in countries with high TB incidence
• Provides some protection to children against most
  serious forms of disease, but not from TB
  infection
• Threat of TB for most children in U.S. does not
  warrant widespread inoculation
• BCG's ability to prevent TB in adults is highly
  uncertain

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BCG (2)

• BCG sometimes causes false-positive
• CDC recommends BCG only when
• Infant or child will be continually exposed to
  untreated or partially treated patient with
  infectious pulmonary TB or MDR-TB
• Health worker is continually exposed to MDR-TB in
  situations where infection control precautions
  have not been successful

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BCG (3)

• BCG and TST
• Person with BCG history may resist TST because
  he/she believes that BCG will provoke
  "false-positive" reaction
• BCG history usually will not affect TST results
  (unless BCG given repeatedly or in last year)
• BCG in infancy does not cause positive TST in
  adults
• CDC advises clinicians to ignore BCG history when
  interpreting TST results

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Review Questions

• Complete this sentence
• TST technicians use the method of TST
• What are the 3 main steps of the Mantoux method?
• List 6 supplies needed to perform TST

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Review Questions (2)

• Which of the following is FALSE about tuberculin?
• It should be stored at temperatures between
  35-46?F (2-8?C)
• It should be protected from light when not being
  used
• Open vials should be discarded after 30 days
• It is unsafe for pregnant women

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Review Questions (3)

• What are 4 examples of "universal precautions"?
• True or false A TST reaction of gt 5 mm is
  considered "positive" in a person who is a recent
  contact to an active case of TB
• What is a situation in which a "false-negative
  reaction" can occur?
• True or false A person who has a history of BCG
  vaccination should not receive TST