The variability and accurate assessment of microinflammation in haemodialysis patients

Systemic microinflammation is correlated with atherosclerosis. It needs a reliable assessment. This study explores the temporal variations of three inflammatory indexes [C-reactive protein (CRP), serum amyloid A (SAA) and interleukin-6 (IL-6)] in a period free of clinical events and tests the reliability of their multiple measurements for the assessment of microinflammation in haemodialysis (HD) patients, a population at high risk of atherosclerotic cardiovascular disease.

For 4 months, serum CRP, SAA and IL-6 were measured in 29 HD patients during the weeks they were free of inflammatory clinical events (> or =12 measurements for each index in every patient). The components of the variance as well as the reliability of two to five measurements for each index, aimed at assessing microinflammation precisely, were computed.

The median (interquartile range) of CRP was 2.3 (0.9-4.9) mg/l, of SAA 3.7 (2.1-9.3) mg/l and of IL-6 4.4 (2.2-7.7) pg/ml. Patients were approximately equally distributed between three groups of low, intermediate and high variability for each index. The contribution of intraindividual (biological) variation to the total of variance was 71.3%, 69.3% and 86.7% for CRP, SAA and IL-6, respectively (higher than in all other similar studies in healthy populations). Using two measurements, the estimated reliability was 57-68% for CRP in two-thirds of the patients (comparable with that found in healthy subjects) and 57% for SAA and IL-6 in only one-third of the patients. Increasing the number of measurements up to five did not change the reliability.

Individual factors significantly influence the levels of inflammatory indexes in HD patients in periods free of inflammatory clinical events. The mean of two weekly CRP measurements, but not of SAA or IL-6, seems to assess microinflammation in most patients with a sufficient reliability.