The tuberculin skin Test in confirmed pulmonary tuberculosis in the state of Qatar : where we stand

Abstract EN

Objective : This is the first paper to evaluate the potency of the tuberculin skin test (TST) results in confirmed pulmonary tuberculosis in the developing country of Qatar.

Method : Data was collected retrospectively from the tuberculosis (TB) ? treatment unit from 1998 to 2004.

All charts reflected active tuberculosis based on positive sputum smear or culture with documented TST, all of which were reviewed.

The standard TST was done by injecting 0.1 ml of 5 international units subcutaneous RT 23 purified protein derivative (PPD) on volar the surface of the right arm.

Results : There were 306 patients with confirmed active pulmonary tuberculosis, of which 58 % were smear positive and 42 % were smear negative but culture positive.

Expatriates accounted for 81 % (247) and male for 74 % (225) of the patients.

The mean TST was 18.5 mm with standard deviation of 7.54 mm.

TST was less than 5 mm in 8.2 % (25), 5-10 mm in 1,6 % (5), 10-1 5 mm in 11.1 % (34) and more than 1 5 mm in 79.1 %(242).

False negative (reaction less than 10 mm) was significantly higher in Qatar nationals (17 % vs 8 % in expatriates) and those with associated diseases (16.3 % vs 7 % without associated diseases).

Conclusion : Although 9.8 % of confirmed pulmonary tuberculosis had false negative TST, these methods remain a potent aide for epidemiological and diagnostic purposes, and periodic assessment is highly recommended.

In our community, with BCG vaccination, a reaction of more than 10mm should be considered positive.