A study on validity of reading Mantoux test at 24 hours

Abstract

Background: Tuberculosis (TB) is a chronic infectious disease caused by mycobacterium tuberculosis and one of the major disease affecting children throughout the world. Prevalence of active disease in adults in India is 18 per 1000 population. The aim of the current study was to see whether reading Mantoux test at 24 hours can predict Mantoux positivity at 48 hours.Methods: A Prospective observational study was conducted in Tertiary care hospital which caters for people in and around Madurai, Tamil Nadu, India. Total 6560 children in the age group of 6 months to 12 years with suspicion of Tuberculosis. (Positive contact history or Low weight for age or persistent fever for more than 2 weeks or cough for more than two weeks or significant lymphadenopathy) were given Mantoux test. Of these 5904 (90%) children turned up for 24hours and 48 hours reading. Transverse diameter of the induration was measured. More than 10mm was considered as Mantoux positivity. The size of induration at 24 hours and 48 hours were compared.Results: Out of 5904 children, 206 (3.48%) children had Mantoux positivity at 48 hours. Of these 206 children, 131 (63.6%) children had more than 10 mm at 24 hours. Remaining 75 (36.4) showed less than 10 mm at 24 hours, but become more than >10 mm at 48 hours. Overall tuberculin positivity is 3.5%.Conclusions: Positivity of tuberculin test must be confirmed at 48 hours only. There is no standard reading at 24 hours which can be presumed to become positive at 48 hours.