Interleukin-6 is an independent predictor of mortality in patients starting dialysis treatment

Background. The mortality rate is high among end-stage renal disease (ESRD) patients, and recent evidence suggests that this may be linked to inflammation. The activity of interleukin-6 (IL-6) and its soluble receptor (sIL-6R) are markedly up-regulated in ESRD patients, and plasma IL-6 levels predict outcome in haemodialysis (HD) patients. However, it has not been established whether elevated plasma IL-6 also predicts outcome in ESRD patients treated by peritoneal dialysis (PD), and how it relates to the data on HD patients. The predictive power of sIL-6R levels on outcome is also unknown in this patient population. Methods. To determine whether or not plasma IL-6 and sIL-6R predict patient survival, we studied 173 ESRD patients (62% males, 53+/-1 years of age) near the initiation of dialysis treatment (99 PD, 74 HD patients). The patients were followed for a mean period of 3.1+/-0.1 years (range 0.1-7.1 years) and were stratified at the start of dialysis treatment according to age, gender, presence of cardiovascular disease, malnutrition (determined by subjective global assessment), diabetes mellitus, and IL-6 and sIL-6R plasma levels. Results. A significantly different (P<0.0001) mortality rate was observed in different groups when patients were divided into quartiles according to IL-6 levels. Furthermore, the same differences were observed, less notably however, for sIL-6R (P<0.05). When patients were stratified according to IL-6 quartiles and analysed separately according to the different initial treatment groups, a similar profile of survival was observed for PD (P<0.01) and HD (P<0.05) patients. In a Cox proportional hazard model adjusting for the impact of age, malnutrition, diabetes mellitus and male gender, log IL-6 values were independently associated with poor outcome (P<0.05). Conclusions. The present study demonstrates that the strong predictive value of elevated IL-6 levels for poor outcome in ESRD patients is similar in both HD and PD patients starting treatment.