Skin testing is still the best method of testing for latent infection by prior exposure to M. tuberculosis. Intradermal testing with 5 tuberculin units (0.1 mL) of PPD is more accurate than multiprong tine testing. Interpretation depends on the patient's risk of disease. Patients with a history of direct exposure to active cases of TB, or with impaired immunity such as HIV, should be considered to have a positive test if the area of induration is greater than 5 mm at 48 to 72 hours. Most other patients should be considered positive with induration greater than 10 mm. Very-low-risk patients (age >5 years, no history of exposure, normal immune system, low rates of TB in population) may be considered positive only with induration greater than 15 mm. These criteria are summarized in Box 18-5 (CDC, 2000). Persons vaccinated with bacille Calmette-Guerin (BCG) vaccine may still be accurately tested with PPD skin testing. For high-risk populations, a percentage tuberculin response higher than 15 on the QuantiF-ERON-TB test (QFT) performed on venous whole blood is moderately correlated with a positive skin test. Neither PPD nor QFT is recommended as routine screening in low-risk populations (CDC, 2003a).

Clinical diagnosis in endemic areas is often based on history of exposure, clinical signs, AFB smears, and chest x-ray findings. Sputum cultures can confirm the diagnosis and also

Box 18-5 Criteria for Tuberculin Positivity by Risk Group

Mole Removal

Mole Removal

Moles, warts, and other unsightly irregularities of the skin can be bothersome and even embarrassing. They can be removed naturally... Removing Warts and Moles Naturally! If you have moles, warts, and other skin irregularities that you cannot cover up affecting the way you look, you can have them removed. Doctors can be extremely expensive. Learn the natural ways you can remove these irregularities in the comfort of your own home.

Get My Free Ebook

Post a comment