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.

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  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

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