Pre-lecture questions:
1.) Which one of the following is true regarding tuberculin skin testing? A. The injection is intramuscular B. The injection is subcutaneous C. The injection in intradermal D. The injection is intravenous 2.) The injection material is comprised of which one of the following? A. A live attenuated virus B. Purified protein derivatives of the mycobacterial cell wall C. Live attenuated strains of Bacillus-Calmette-Guerin D. Killed strains of Mycobacterim bovis
3.) At which anatomic site should the test be placed? A. Forearm B. Deltoid region C. Abdominal wall D. Gluteal region
4.) How long after the injection should the skin test be read? A. One hour B. Twelve hours C. Twenty four hours D. Forty-eight hours
5.) How should erythema (redness) at the test site be interpreted ? A. Indicative of active tuberculous infection B. Indicative of latent tuberculous infection C. Indicative of an allergy to the testing material D. There is no significance to erythema at the test site
The Tuberculin Skin Test (Mantoux) The tuberculin skin test is a diagnostic tool for the detection of tuberculous infection. The test, referred to as the Mantoux Test, consists of the intradermal injection of a 0.1 milliliter injection of a standardized solution of components of the cell wall of the etiologic agent of tuberculosis, Mycobacterium tuberculosis. The dose of testing material administered in the standard test is 5 Tuberculin Units (5TU). This is considered to be an intermediate strength test. Full strength (250 TU) is occasionally administered when there is doubt about the ability of a patient to mount a response to the 5 TU test.
The Mantoux is administered to persons considered to be at risk for having tuberculous infection. In populations at low risk for Mycobacterium tuberculosis infection, positive tests are likely to be the result of cross reactions with other environmental mycobacteria. The Mantoux does not distinguish infection from active disease. In fact, ten percent of persons with active disease may be non-reactors due to other underlying conditions such as malnutrition, malignancy and alcohol use. HIV infected persons lose tuberculin reactivity as their immune suppression progresses. Test Administration The Mantoux Test is administered as follows: Supplies: One, 1 cc Tuberculin Syringe with 0.1 cc gradations Alcohol swabs One, 5cc vial of Purified Protein Derivative (PPD) One, flexible millimeter ruler 1. Unsheath needle on tuberculin syringe. 2. Draw air into the syringe. 3. Remove protective cape from vial of PPD and swab top with alcohol wipe. 4. Insert tuberculin syringe into vial of PPD and inject air. 5. Withdraw PPD solution into the syringe to a level just beyond the 0.1 cc mark on the syringe. 6. Identify a site for the injection on the anterior surface of the forearm in an area where there are no obvious blood vessels. 7. Using an alcohol wipe, decontaminate the area. 8. Hold the tuberculin syringe in a level position in your dominant hand with the thumb above and the second, third and fourth fingers beneath the barrel of the syringe. The bevel of the needle should be facing up. 9. Place the fingers of the non-dominant hand under the forearm to be tested and the thumb near the test site, being careful not to contaminate the site. With the thumb, pull back on the skin near the test site to create a smooth flat surface for injection. 10. Approach the test site with the syringe nearly parallel to the skin surface. 11. Insert the needle to a point beyond the opening of the beveled opening on the needle. 12. Gently, draw back on the plunger of the syringe to be sure there is no blood return. 13. Inject the test material, slowly raising a white 5-10 millimeter wheal on the skin surface. 14. If there is no wheal, raised or if there is significant leakage of test material out of the puncture site another test should be placed immediately at an adjacent site. 15. The wheal will resolve in a few hours. 16. The test should be interpreted in 48-72 hours. Immunologic Basis for the Mantoux The basis for the Mantoux Test is T-cell responsiveness to mycobacterial antigens. A cutaneous, delayed type hypersensitivity reaction develops at the site of the intradermal injection 48-72 hours following injection. A positive reaction is characterized by a firm, irregular area of induration (swelling) at the injection site. The site may also become erythematous and pruritic. These reactions are not relevant to the interpretation of the test. Erythema is often mistakenly interpreted as part of the reaction. Erythema at the test site is not indicative of tuberculous infection and often occurs when there is no reaction to the Mantoux.
Measuring the Tuberculin Reaction Forty-eight to seventy two hours after placement the Mantoux should be interpreted. The site should be examined in a well lit room and viewed perpendicular to the axis of the forearm. When interpreting the Mantoux, the site of injection should be palpated to assess for induration. If induration is present, the margins of the indurated area should be indentifed and marked with a pen. Identifying the margins is the most important step in the interpretation process and requires great care and some experience. The skin surface should be stroked with a fingertip in the direction of the indurated area in order to identify a change in the texture and conformation of the skin which demarcates the edge of the ractive site. This process should be repeated from several directions to identify the margins of the induration. The greatest diameter of the indurated site should be measured and recorded in the patient's chart. Tuberculin reactions should never be recorded as positive or negative - the size of the reaction should always be noted in the patients record. Interperating the Test Results
The following criteria should be applied to tuberculin reactions to determine whether preventive therapy is required:
0 - 5 millimeters induration: no prophylaxis 5 - 10 millimeters induration: Prophylaxis indicated in the following situations a. Household contacts of a known case of tuberculosis b. HIV infected persons c. Persons with a radiographic evidence of old tuberculosis with a history of never having been treated or prophylaxed 10 - 15 millimeters of induration: prophylaxis is indicated in the following situations a. patients with underlying medical conditions such as diabetes mellitus, renal failure, gasterctomy, loss of > 10% of ideal body weight, malignancies, health care workers Ø 15 millimeters: prophylaxis is indicated in the following situations: b. for reactions of this size in persons with no known risk factor for tuberculosis
Persons with a greater than 10 millimeter increase in their tuberculin reaction within the past two years are considered to be have converted their skin test (i.e., become newly infected with Mycobacterium tuberculosis). Newly infected persons, children, immunocompromised persons and persons with underlying medical conditions are at the greatest risk for developing active tuberculosis and therefore require preventive therapy.
A review of symptoms and a chest x-ray film should be obtained on all tuberculin reactors to assess for evidence of active disease. Those who are symptomatic or with abnormal x-ray films should undergo more thorough evaluation including sputum culture for Mycobacterium tuberculosis. Infection with Mycobacterium tuberculosis confers a lifetime risk of approximately 10% of developing active disease. The greatest risk is within the first two years after infection. Immunocompromised persons, particularly HIV infected persons, and those with underlying medical conditions are at particular risk because of their loss of the T-cell immunity necessary to maintain infection a latent state. Children are at increased risk for extrapulmonary and disseminated disease. Immunocompromised persons and children may receive preventive therapy immediately following a significant exposure situation in order to prevent early progression to disease.
Isoniazid prophylaxis (300mg orally, daily for six months) for Mycobacterium tuberculosis infection reduces the risk of progression to active disease by approximately 85% for persons who complete six months of therapy. HIV infected person should receive prophylaxis for a year. Children under the age of twelve require nine months of prophylaxis. Persons who have active tuberculous disease, rather than infection, require a minimum of two drugs for treatment and usually initiate therapy with four drugs. Persons over the age of 35 are at increased risk of hepatotoxicity from isoniazid and should be followed regularly (every 4-6 weeks) with clinical examinations, symptom review and liver function tests to search for evidence of adverse effects. Symptoms suggestive of hepatitis (nausea, fatigue, dark urine, right upper quadrant abdominal discomfort) or an increase in the serum transaminase levels to > five times normal should result in immediate discontinuation of treatment.
Post-lecture questions: 1.) Which one of the following is true regarding tuberculin skin testing? A. The injection is intramuscular B. The injection is subcutaneous C. The injection in intradermal D. The injection is intravenous 2.) The injection material is comprised of which one of the following? A. A live attenuated virus B. Purified protein derivatives of the mycobacterial cell wall C. Live attenuated strains of Bacillus-Calmette-Guerin D. Killed strains of Mycobacterim bovis
3.) At which anatomic site should the test be placed? A. Anterior forearm B. Deltoid region C. Abdominal wall D. Gluteal region
Correct Answers:
1.) C. 2.) B. 3.) A. 4.) D. 5.) D.