Exploring inflammation in hemodialysis patients: persistent and superimposed inflammation. A longitudinal study.

Background: Inflammation is frequently elevated, and seems to be episodic in hemodialysis (HD) patients. Whether, its episodic character is due to the temporal variability, in periods free of clinical events, of the inflammatory indices or due, to the acute phase response induced by common inflammatory stimuli, has not been investigated yet in a longitudinal study. This study explores inflammation forms, characteristics and causes which are probably related to the high cardiovascular disease (CVD) morbidity in HD patients.

Methods: In 37 HD patients, high-sensitivity C-reactive protein (hs-CRP), serum amyloid A (SAA) and interleukin-6 (IL-6) were weekly measured for 16 consecutive weeks. Inflammatory clinical events, in the week before every measurement, were recorded. Repeated measures ANOVA were applied for statistical analysis.

Results: Fifty-one of 533 patient-weeks were positive for a clinical event. Mean +/- SD (range) hs-CRP was 7.01 +/- 16.06 (0.2-169) mg/l for all the weeks of the study, 38.25 +/- 39.35 (2.1-169) mg/l for the weeks with clinical events and 3.70 +/- 3.86 (0.2-26.1) mg/l for the weeks free of events. Variations for SAA and IL-6 were similar. 'Clinical events' strongly influenced acute-phase proteins and IL-6 levels. The effect of the factor 'time' (as assessed by inflammatory indices variation in weekly repeated measurements) was significant for all the 3 indices measured, independently of the factor 'clinical events'.

Conclusions: In periods free of clinical events, microinflammation characterizes HD patients and fluctuates in time. Inflammation due to common clinical events is added, periodically, to this microinflammation. The high level persistent microinflammation as well as the superimposed--due to clinical events--inflammation could be related to the CVD in these patients.