Indications, Interpretation and Clinical Consequences of Tuberculin Skin Tests in Resource Limited Settings

Abstract

Objective: to evaluate the policy of TST testing in Suriname. As there is no gold standard to diagnose latent tuberculosis infection (LTBI), the tuberculin skin test (TST) is used to diagnose LTBI. However, internationally, the cut-off values of the TST are not uniform and depend on local tuberculosis (TB) epidemiology and guidelines for test initiation. In Suriname, where currently several indications exist for TSTs, cut-off values are set at 5 mm or 10 mm, depending on the age and/or medical history of the patient. LTBI classification is performed by pulmonologists primarily based on the American Thoracic Society targeted TB testing guidelines. Method: retrospective analysis of outpatient TST data between 2011 and 2019 from Suriname’s sole pulmonary medicine clinic. Result: 1373 patients were evaluated. 590 patients were from the screening group of whom 253 had a positive TST result, 46 of whom were classified as LTBI. In the contact tracing group of 649 patients, 616 had a positive TST, 352 of whom were classified as LTBI. In the medical condition group of 134 patients, 96 had a positive TST, 38 of whom were classified as LTBI. Eventually, positive TST results were found for 965 tested patients: 436 patients were classified as LTBI and 529 non-LTBI patients were not prescribed chemoprophylaxis. None of the non-LTBI TST-positive patients were diagnosed with active TB, including 174 patients with a TST result of 15 mm or greater and in need of IPT, but not prescribed by judgement of the pulmonologist or because of loss to follow-up. Conclusion: the overrepresentation of positive TST results in Suriname is attributable to stringent cut-off values, especially among patients who do not disclose TB risk factors. In our opinion the TST cut-off value for such patients in Suriname and other similar settings could be set at 15 mm. We also promote that for all patients with a TST result of 15 mm or greater, offering IPT should be considered (after excluding active TB).