Current guidelines for what constitutes a positive TB skin test among corticosteroid pill users may not be capturing all those who are infected, said Dr. Nicholas Vozoris, a respirologist in the Tuberculosis Program at St. Michael's Hospital. Previous research has shown that people who take corticosteroid pills, such as Prednisone, and have inhaled the TB bacteria, have an eight times higher risk of the bacteria becoming active than people who are not taking the drugs. Dr. Vozoris said that would suggest they should be screened more often for TB infection.
However, an examination of more than 7,300 people in the U.S. National Health and Nutrition Examination Survey found this was not the case. The survey, a series of studies designed to assess the health and nutritional status of adults and children in the United States, is unique in that it combines interviews and physical examinations. The findings were published today in the European Respiratory Journal
He found that although taking corticosteroid pills was a risk factor for turning latent TB into active TB, those patients were screened less often for TB than others. They were also less likely to be prescribed TB-fighting drugs prophylactically. Dr. Vozoris said that for the general population, producing a bump at least 10 millimetres in diameter following a TB skin test likely means that one has inhaled the TB bacteria. Current guidelines recommend that the bump be only five millimetres long if the patient is taking corticosteroid pills, but Dr. Vozoris said there is no evidence to support that is the correct cut-off. The study results show that 3.5-mm might be a more appropriate cut-off. Corticosteroid pills are commonly prescribed for people with asthma, chronic obstructive pulmonary disease, inflammatory bowel disease, inflammatory arthritis and cancer. They work by decreasing inflammation, but they also suppress the immune system. The Respirology Division of St. Michael's Hospital has a Tuberculosis Program dedicated exclusively to caring for patients with TB disease and infection. The program's clinic has 1,900 patient visits a year, making it one of the largest TB clinics in Canada.