PURPOSE: Tuberculin skin test (TST) represents a valuable tool in tuberculosis (TB) control. In contries with obligatory BCG vaccination such as the Czech Republic, the results are influenced by BCG. Other factors modifying the value of TST might be an immunological status, age and comorbid illnesses. The aim of our study was to analyze the results of TST in a large number of TB patients in the Czech Republic.
METHODS: We evaluated the values of TST in 1172 consecutive patients with bacteriologically confirmed TB in the years 2003-2004. Data concerning TST and comorbidities were obtained from the National Register of Tuberculosis. Age and comorbidities were compared with TST results. •2 test with Yates correction was used for statistical analysis between the groups.
RESULTS: TST was positive in 842 patients (72 %), 330 patients with TB had negative TST (28%). The average age in the whole group was 56 years. The average value of TST for all patients was 11.6 mm, the median 12 mm. In patients younger than 30 years the average value of TST was 15 mm, 14 % of this age group was negative. In the age group 70 years and older the average value of TST was 17 mm, 42% of this group was negative. The difference between the percentages of TST negative patients is significant. 133 patients with chronic liver disease had significantly lower values of TST compared to age-matched controls with TB. The same was true for 163 patiets with diabetes mellitus and 76 patients with malignancy.
CONCLUSION: The results of TST in a large group of TB patients are dependent on the age and comorbid ilnesses. TST should be used as a reliable tool for evaluation of latent tb infection in a vaccinated population preferentially in younger adults with no comorbidities.
CLINICAL IMPLICATIONS: In vaccinated population the TST in TB patients is age dependent and influenced by commorbid illnesses.
DISCLOSURE: Jiri Homolka, None.