A 36-year-old woman who lives in the southern United States comes to the physician for a tuberculin skin test. She will be volunteering in her daughter's school cafeteria, and the school district requires tuberculin testing by law. She says that she feels "perfectly fine" and has never been tested for tuberculosis. The patient has no ill contacts and no underlying medical conditions. She was born in the United States, is not a health care worker, and has never been incarcerated. Two days after intradermal injection of the Mycobacterium tuberculosis purified protein derivative, there is a 12-mm induration. What is the best next step in management of this patient?

Question

A 36-year-old woman who lives in the southern United States comes to the physician for a tuberculin skin test.  She will be volunteering in her daughter's school cafeteria, and the school district requires tuberculin testing by law.  She says that she feels "perfectly fine" and has never been tested for tuberculosis.  The patient has no ill contacts and no underlying medical conditions.  She was born in the United States, is not a health care worker, and has never been incarcerated.  Two days after intradermal injection of the Mycobacterium tuberculosis purified protein derivative, there is a 12-mm induration.  What is the best next step in management of this patient?

Quizplus · Accepted Answer

Explanation: 11ec25c8_d0ee_a43e_bc81_d1094d993979_MD0003_00 Tuberculin skin testing (TST) is used to identify asymptomatic patients with prior exposure to Mycobacterium tuberculosis and latent tuberculosis (TB) infection. It consists of an intradermal injection of purified protein derivative (PPD) from M tuberculosis on the inner surface of the forearm (Mantoux technique). The response is assessed by the delayed hypersensitivity response measured by the size of induration (not erythema) 48-72 hours after PPD administration. The TST reaction size is interpreted in the context of patient risk factors and pretest probability to determine a positive or negative response. This patient is completely asymptomatic, has no history of TB exposure, and has no comorbid medical conditions that increase the risk of reactivation. She is a healthy person with low likelihood of TB infection. In such patients, United States guidelines use a cutoff value of ≥15 mm as a positive TST result; therefore, the 12-mm induration in this patient (<15 mm) is considered a negative TST result (Canadian guidelines use a cutoff value of 10 mm). The reason for the higher cutoff in such patients is the high likelihood of exposure to nontuberculous mycobacteria in several parts of the southern United States, which would increase the false-positive response if lower cutoff values are used. In such patients who are unlikely to be infected, testing for latent TB is not generally recommended but may be required by law (as in this case): In case of a negative result (eg, TST <15 mm), no further management is recommended. In case of a positive result, repeat testing (eg, repeat TST or interferon-γ release assay [IGRA]) should be considered to exclude a false-positive. IGRA can be used instead of TST for either initial or repeat testing but may not always be available (eg, cost). (Choice A) A complete clinical evaluation, including detailed history, physical examination, and chest x-ray, should be obtained in patients with a positive tuberculin skin test to rule out active TB. Patients with a positive response and no signs of active TB infection (negative x-ray) should be treated for latent TB infection. Given her low pretest probability of TB, this patient's TST result <15 mm is considered negative. (Choices B and C) There are several acceptable treatment regimens for patients with latent TB infection. Treatment with 9 months of isoniazid (INH) with pyridoxine supplementation or 3 months of once-weekly INH and rifapentine given by direct observed therapy are the preferred options. INH for 6 months and rifampin for 4 months are acceptable regimens. This patient had a negative response, does not have latent TB infection, and should not be treated. treatment regimens (Choice D) A treatment option for active pulmonary TB is the combination of 4 drugs (isoniazid, rifampin, ethambutol, and pyrazinamide) for 8 weeks (2 months). This is then followed by a continuation phase of combined therapy with isoniazid and rifampin for an additional 4 months (total of 6 months). This patient does not have active TB. Educational objective: Tuberculin skin testing is used to identify patients with latent tuberculosis (TB) infection and a high risk of reactivation TB. In the United States, an induration size of <15 mm is considered negative (ie, ≥15 mm is considered positive) in healthy patients with a low likelihood of TB infection.

A 36-Year-Old Woman Who Lives in the Southern United States