Variability of effluent cancer antigen 125 and interleukin-6 determination in peritoneal dialysis patients.

BACKGROUND Cancer antigen (CA) 125 is a glycoprotein that provides data on the state of the peritoneal membrane in peritoneal dialysis (PD). Interleukin-6 (IL-6) acts as a mediator in acute-phase responses. The study evaluated the usefulness of CA125 and IL-6 in random effluent samples, by assessing their variability in individual patients during clinical practice at the outpatient department. METHODS This longitudinal prospective study was conducted from 2007 till 2009. Participants included 52 stable PD patients aged ≥ 18 years. Effluent samples were obtained during regular outpatient visits and appearance rates (ARs) were calculated. Inter- and intra-individual variability was determined by the coefficient of variation (CV). A linear mixed model was used to analyse time courses. Furthermore, release patterns of these effluent markers were studied. RESULTS CA125-AR of short-term patients (≤ 24 months) ranged from 39.2 to 766.7 U/min and IL-6-AR from 15.5 to 220.0 pg/min. Long-term patients (≥ 25 months) had a CA125-AR of 7.3-1534.0 U/min and IL-6-AR of 6.9-956.4 pg/min. Overall, CV(intra) was 15% in effluent CA125-AR and 28% in IL-6-AR. Intermediate sampling during a 4-h dwell showed a linear increase of CA125 and IL-6 effluent concentrations. The trend of CA125-AR was different (P = 0.001) between short- and long-term patients. A negative relationship was found between CA125 (r = -0.44, P = 0.02) and PD duration. CONCLUSIONS The clinical relevance of effluent CA125 determinations from an unstandardized dwell during every outpatient visit is reasonable, as judged from the CV(intra). The inferior CV(intra) values of ARs as compared to effluent values indicate that ARs should only be calculated under standardized conditions. A single IL-6 measurement, as a predictor of outcome, should be interpreted cautiously.