[Tuberculin test responses of tuberculosis patients]

Abstract

Objective: To determine the response of tuberculosis patients to tuberculin skin tests.

Method: The results of skin tests used for initial assessment of tuberculosis patients in Catalonia were reviewed (Multicenter Tuberculosis Research Project). Negative skin tests were those with indurations < 5 mm; positive tests were those with indurations measuring > or = 5 mm. Individuals were classed as having or not having risk factors for developing tuberculosis and those without risk factors were classified by age, location and extension of tuberculosis.

Results: Negative skin tests were seen in 1,566 patients (23%). Negative tests were more common in patients with risk factors, significantly so in those undergoing immunosuppressant therapy (50%) or with HIV infection (61%). Negative tests were less prevalent in patients with no risk factors (13%) and, among them, in children (1%), in patients between 15 and 29 years of age (10%) or in those with non-pulmonary forms (10%). Negative tests were significantly more prevalent among patients 60 to 74 years of age (27%), those over 74 (44%), and those whose disease was pulmonary and extrapulmonary (26%) or disseminated (64%). No significant differences in induration size of positive skin tests were observed for patients with and without risk factors (including HIV infection or non-infection). A normal distribution of induration size was observed in all groups.

Conclusions: A negative tuberculin skin test for initial assessment should be interpreted in function of the presence or absence of risk factors, age, location or extension of tuberculosis. When a skin test is positive, the response will be similar whether or not an immunodepressant factor is present.