Thyroid function levels and risk of bloodstream infections in a general population

What is it about?

The objective of this study was to investigate the relationship between thyroid-stimulating hormone (TSH) levels within the normal range and the risk of bloodstream infections (BSI) and BSI-related mortality in the general population. We aimed to provide clarity on previous conflicting findings regarding the association between thyroid function and infection risk, which often arose from studies conducted in intensive care units where nonthyroidal illness syndrome (NTIS) may be present. The study followed a prospective design, meaning that participants were followed over time to observe any occurrences of BSIs and BSI-related deaths. The participants included 34,619 individuals who had their TSH levels measured during the HUNT2 study conducted between 1995 and 1997. The main measurements used in the study were hazard ratios (HRs) with a 95% confidence interval (CI) using Cox regression. These ratios were used to assess the association between TSH levels and the risk of BSIs and BSI-related mortality up until 2011. The results of the study showed that, during a median follow-up period of 14.5 years, 1179 participants experienced at least one episode of BSI, and 208 individuals died within 30 days after a BSI. TSH levels within the normal reference range (0.5-4.5 mU/L) were not found to be associated with the risk of a first-time BSI, with an HR of 0.97 (95% CI: 0.90-1.04) per mU/L. However, when the analysis was stratified by age, a weak inverse association between TSH levels and BSI risk was observed only in individuals below 65 years of age (HR: 0.88; 95% CI: 0.78-1.00 per mU/L). The study also found that individuals with any baseline thyroid disease had a 30% increased risk of BSI, while those with hyperthyroidism had a 57% increased risk, and those with hypothyroidism had a 20% increased risk. However, it is important to note that these associations may be influenced by other factors related to overall health. Regarding BSI-related mortality, the study did not find a clear association with TSH levels. However, the imprecision of the hazard ratios in this analysis was due to the small number of BSI-related deaths. In conclusion, this study provided some evidence of a weak inverse association between TSH levels and the risk of BSI in individuals below 65 years of age. The increased risk observed in individuals with thyroid disease is likely explained by other factors related to concurrent ill health.

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Why is it important?

Increased knowledge about modifiable causes of BSI is important for this potentially deadly disease, and where survivors often experience sequalae

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