805 Assessing the efficacy of the mantoux test and interferon gamma release assay in paediatric TB Diagnosis

Abstract

<h3>Aims</h3> Mantoux and Interferon Gamma Release Assay (IGRA) are the two principal tests used in the assessment of children with TB, particularly in high-risk individuals such as those who have moved to the UK from areas where TB is more prevalent. Mantoux utilises the injection of PPD tuberculin into the skin of the forearm and observing a skin reaction at the injection site over the next 48 – 72 hours. IGRA is a blood test that measures a person’s response to <i>Mycobacterium tuberculosis</i>. There are two main types of IGRA, the Quantiferon Gold test and T-spot test. In this study, a retrospective audit of paediatric TB cases was performed to compare these two tests in their ability to inform the diagnosis of pulmonary and extra-pulmonary TB in a paediatric population. <h3>Methods</h3> This study considered 77 patients with active paediatric TB who were diagnosed at a tertiary paediatric unit between January 2011 and March 2021. Data was collected on these patients using electronic records and then entered on a pro forma. These results were then analysed and the sensitivity of the Mantoux and IGRA tests were calculated and compared in pulmonary and extra-pulmonary TB. Extra-pulmonary TB in this case considers lymph node, CNS and gastrointestinal TB. <h3>Results</h3> The Mantoux test had an overall sensitivity of 90% (27/30). In pulmonary TB this sensitivity falls slightly to 88% (23/26) whilst for extra-pulmonary TB it showed a 100% (4/4) sensitivity (figure 1). The Quantiferon TB Gold test was the primary IGRA test used in this study, and it exhibited an overall sensitivity of 88% (65/74). Quantiferon was positive in 92% (59/64) of pulmonary TB patients and 63% (10/16) of extra-pulmonary TB patients. Just 2 patients were not tested for IGRA (figure 2). The levels of Quantiferon sensitivity were found to be higher in ages five and above (91%, 49/54) than in patients below the age of five (80%, 16/20). <h3>Conclusion</h3> The sensitivity rates for Mantoux and IGRA are similar to the results from previous studies.¹ However, the fact that IGRA has a higher sensitivity than Mantoux, particularly for pulmonary TB, contrasts with most previous research and aligns with the current guidelines in our trust. This audit also demonstrates the utility of combining Mantoux and IGRA tests as Quantiferon was found to be less effective in patients younger than five years old and 4/9 Quantiferon negative patients in this audit tested positive via the Mantoux test.² Finally, the difference in sensitivity for pulmonary and extra-pulmonary TB using Quantiferon TB Gold was substantial (92% vs. 63%), indicating a potential deficiency in this test for extra-pulmonary TB. <h3>References</h3> Sali M, Buonsenso D, Goletti D, D’Alfonso P, Zumbo A, Fadda G, <i>et al</i>. Accuracy of QuantiFERON-TB gold test for tuberculosis diagnosis in children. <i>PLoS ONE</i> 2015;<b>10</b>(10). Nolt D, Starke JR. Tuberculosis infection in children and adolescents: testing and treatment. <i>Pediatrics</i> 2021;<b>148</b>(6).