Impact of diabetes on TB infection diagnosis

Tuberculosis (TB) remains a major global health threat and is linked to diabetes, forming a syndemic hindering WHO's End TB Strategy. Diabetes disrupts immunity, increasing TB risk and severity, potentially affecting diagnostic tests accuracy for TB infection (TBI). TBI diagnosis relies on immune response detection by skin tests or Interferon-γ release assays (IGRAs) in individuals without symptoms, radiological, and microbiological evidence of TB disease. TBI tests vary in accuracy when immunity is impaired. Literature on the impact of diabetes and glycemic control on test accuracy is inconsistent, with studies reporting higher IGRA positivity in diabetics, and others reporting reduced sensitivity or indeterminate results. There is insufficient evidence that antidiabetic drugs affect IGRA or skin test accuracy for TBI diagnosis. Interestingly, insulin or metformin therapy was associated with lower TBI prevalence, suggesting that glycaemic control may be associated with protection from TBI. Data on the impact of diabetes and comorbidities on TBI diagnostic accuracy remain limited. Overall, poor glycaemic control, advanced age, HIV-infection, chronic kidney disease, and immunosuppressive therapy can reduce test sensitivity, leading to false negative scores and underdiagnosis. Further research is needed to clarify these effects and guide WHO preventive strategies in the TB-diabetes syndemic.