Tuberculin skin test - Detailed Information

The tuberculin skin test is a delayed hypersensitivity reaction to tuberculin. It indicates infection with a variety of non-tuberculosis mycobacteria, previous infection with M. tuberculosis or BCG vaccination (with the live attenuated mycobacterial strain of M. Bovis).

  • Tuberculosis skin test:

    • It is used as an aid in the diagnosis of tuberculosis (TB) infection.

Tuberculin Dose in Adults

Dosage in Tuberculin skin test:

  • Intradermal: 5 units are given (0.1 mL)

Dosage in TST interpretation:

  • Criteria for positive TST read at 48 to 72 hours :

    • Induration ≥5 mm:

      • Patients with recent close contact with a person with known active TB,
      • HIV infection (or risk factors for HIV infection, but unknown status),
      • patients with chest x-ray consistent with prior TB,
      • patients with organ transplants and
      • immunosuppressed patients receiving prednisone at a dose of 15 mg/day or more  for one month or more
    • Induration ≥10 mm:

      • Patients with clinical conditions that increase the risk of TB infection,
      • IV drug users,
      • mycobacteriology laboratory workers,
      • recent immigrants (ie, ≤5 years) from high-prevalence countries residents and employees of high-risk congregate settings,
      • children <4 years of age, or
      • infants, children, and adolescents exposed to adults at high risk
    • Induration ≥15 mm:

      • Patients who do not fit in any of the above criteria (no risk factors for TB)
      •  A two-step test is recommended when testing will be done at regular intervals (eg, for health care workers).
      • If the first test is negative, a second TST should be done 1 to 3 weeks after the first test was read.

  • TST interpretation  in a health care setting (CDC 2005):

    • Baseline test:

      • ≥10 mm is considered positive (either first or second step)
      • 0 to 9 mm is considered negative
    • Serial testing without known exposure:

      • Increase of ≥10 mm is considered positive
    • Known exposure:

      • ≥5 mm is considered positive in patients with a baseline of 0 mm
      • ≥10 mm is considered positive in patients with negative baseline or previous screening result of >0 mm

Tuberculin Dose in Childrens

Tuberculin skin test:

  • Infants ≥6 months, Children, and Adolescents:
    • Use adult dosing.

Pregnancy Risk Factor: C

  • Studies on animal reproduction have not been done.
  • It is not contraindicated to test during pregnancy.

Breastfeeding: Tuberculin skin test

  • It is unknown if tuberculin purified proteins derivative (PPD), is present in breast milk.
  • Manufacturer advises caution when administering tuberculin testing to nursing mothers.

Tuberculin Dose in Renal Disease:

There are no dosage adjustments given in the manufacturer's labeling.

Tuberculin Dose in Liver Disease:

 There are no dosage adjustments given in the manufacturer's labeling. 

Rare side effects:

  • Cardiovascular:

    • Presyncope
    • Syncope
  • Dermatologic:

    • Erythematous Rash
    • Localized Erythema
    • Localized Vesiculation
    • Rash At Injection Site
    • Skin Rash
    • Skin Ulceration At Injection Site
    • Urticaria At Injection Site
  • Hypersensitivity:

    • Anaphylactoid Reaction
    • Anaphylaxis
    • Angioedema
    • Hypersensitivity Reaction
  • Local:

    • Injection Site Reactions
    • Discomfort At Injection Site
    • Hematoma At Injection Site
    • Injection Site Scarring
    • Local Pruritus
    • Localized Edema
    • Local Tissue Necrosis
    • Pain At Injection Site
  • Respiratory:

    • Dyspnea
    • Stridor
  • Miscellaneous:

    • Fever

Contraindication to Tuberculin skin test Include:

  • Hypersensitivity to tuberculin purified proteins derivative (PPD) and any part of the formulation
  • Previous severe reactions to tuberculin skin test
  • Active Tuberculosis, history of treatment for M. TB infection, or other disease
  • Eczema or severe burns.

Warnings and precautions

  • Viral infections
    • Major viral infections can delay skin testing.

Tuberculin skin test: Drug Interaction

Risk Factor D (Consider therapy modification)

Vaccines (Live)

May diminish the diagnostic effect of Tuberculin Tests. Management: If a parenteral live vaccine has been recently administered, a scheduled PPD skin test should not be administered for at least 4-6 weeks following the administration of the vaccine. Exceptions: Cholera Vaccine.

Monitoring Parameters:

Monitor for immediate hypersensitivity reactions for about 15 minutes following injection. 

How to perform a Tuberculin Skin Test?

  • For intradermal administration only
  • do not administer IV, IM, or SubQ.
  • Apply to the upper third of the forearm (palm up) ≥2 inches from the elbow, wrist, or other injection sites.
  • If neither arm can be used, then administer to back of the shoulder.
  • Avoid skin that is red or swollen
  • Avoid visible veins.
  • Apply using a 27-gauge needle or finer tuberculin syringe.
  • Should form wheal (6 to 10 mm in diameter) as the liquid is injected which will remain almost 10 minutes.
  • Do not apply pressure or bandage at the injection site.
  • Should wheal does not form, repeat the test immediately at another site, at least 2 inches from the first site and circle the second injection site as an indication that this is the site to be read.
  • Document date and time of injection, the person placing TST, location of the injection site, and a lot number of solutions.
  • Read the Tuberculin skin test at 48 - 72 hours following placement.
  • Test results are documented in millimeters even if classified as negative.
  • Erythema and redness of the skin are not indicative of a positive test result.

Mechanism of action of Tuberculin skin test:

  • Tuberculosis can lead to an individual becoming sensitive to antigenic components from the M. tuberculosis organism.
  • Tuberculins can be found in culture extracts that are used to test tuberculin skin preparations.
  • These culture extracts are intracutaneously injected and cause a classic delayed (cellularly) hypersensitivity reaction.
  • The peak reaction takes place after 24 hours. There is induration secondary to cell infiltration and some vesiculation or necrosis.
  • It indicates infection with a variety of non-tuberculosis mycobacteria, previous infection with M. tuberculosis or BCG vaccination (with the live attenuated mycobacterial strain of M. Bovis).

The onset of action: Delayed hypersensitivity reactions: 5 to 6 hours

Peak effect: 48 to 72 hours

Duration: Reactions subsides after a few days

International Brands of Tuberculin:

  • Aplisol
  • Tubersol

Tuberculin Brands in Pakistan:

Mantoux test PPD skin test 

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