Age-related limitations of interleukin-6 in predicting early mortality in acute ST-elevation myocardial infarction

Interleukin-6 (IL-6) is an inflammatory cytokine whose levels increase significantly during myocardial infarction (MI). It has been hypothesised that the concentrations of IL-6 at admission may be useful in prognosticating long-term outcomes. It is unclear, however, whether IL-6 could improve the prognosis of early mortality in MI. We have compared serum IL-6 levels and analysed the disease course in 158 patients with ST-elevation MI (STEMI) who either survived (n = 148) or died (n = 10) within 30 days following the admission. Patients were treated in a single university centre with primary percutaneous coronary intervention (PCI). The non-survivors (6.3%) displayed most of typical risk factors for poor outcome. In addition they had significantly higher concentrations of IL-6 at hospital admission (median values 8.5 vs. 2.0 pg/ml; p = 0.038). However, they were also significantly older than the survivors (median values 72 vs. 57 years; p = 0.0001). IL-6 levels are known to increase with age and we could confirm a significant correlation between patients' calendar age and circulating IL-6 (p = 0.009). Regression analysis revealed that IL-6 concentrations were significantly affected by patients' age but they did not independently relate to patients' outcome. Such results indicate that circulating IL-6 at admission may be of limited value in predicting early mortality in STEMI. It is important to recognize that, because of the small group of patients who died (N = 10), the results must be interpreted with caution. Therefore, we stress that these results should be viewed as preliminary and further validated in a larger set of patients.