The effect of fish oil on two-step tuberculin test in hospitalized patients: A randomized controlled trial

Background: According to national tuberculosis control guide, two-step tuberculin skin test (TST) should be done in the elderly, if the initial test is negative. However, it raises questions about the usefulness of this approach. Objective: This study aimed to explore the effects of fish oil supplements on the two-step tuberculin test in hospitalized patients. Methods: In this randomized controlled clinical trial, 128 patients randomly allocated to control group (receiving placebo, n=64) and treatment group (receiving fish oil supplements, n=64) during 2016. Fish oil supplement group was treated with 2 g daily for 4 consecutive days. The outcome was considered a change in 2 sequential TST induration sizes. Significant increase in the size of the secondary induration compared to primary was considered 6 mm or more. Findings: There was significant difference between primary and secondary indurations of two groups (higher in treatment group) (P=0.04). According to the results of analysis of variance and correlation tests, two effective factors were identified: initial induration and residence location (P=0.014 and P=0.002, respectively). In both groups, no clinically significant increase in the size of induration was observed. Conclusion: It seems that the number of cases considered as infected with tuberculosis does not increase with two- rather than one-step tuberculin skin test. Also, the short-term administration of fish oil supplements does not change this result.