Longitudinal Study of Proteins in Plasma and Dialysate during Continuous Ambulatory Peritoneal Dialysis (CAPD)

The aim was to evaluate plasma proteins during continuous ambulatory peritoneal dialysis (CAPD) in relation to dialysis losses, membrane permeability, renal insufficiency, and time on CAPD. Ten male patients, established on CAPD for at least 14 months, were studied every 8 weeks for 56 weeks. Blood and dialysate from the morning exchange were analysed for urea, creatinine, and 7 proteins, and used to calculate dialysate to plasma concentration ratios (DIP). These ratios were not significantly changed suggesting that permeability remained constant. However, there was a trend for β2-microglobulin, creatinine, and urea to increase progressively. After 56 weeks, β2-microglobulin had increased from 27.9 to 31.3 mglL (p < 0.05) and creatinine 1006 to 1099 μmoLIL (p < 0.05) and both correlated with time on CAPD (p < 0.001). Plasma α1-acid glycoprotein, albumin, transferrin, IgG, IgA, and complement C3 were not significantly changed, although IgA and complement C3 were each negatively correlated with time on CAPD (r = −0.70 and −0.67, respectively), creatinine (r = 0.51 and −0.54), and urea (r = −0.61 and −0.61) (p < 0.001 for all). It is concluded that increases in β2-microglobulin, creatinine, and urea are not due to loss of membrane permeability but reflect a slight increase in uraemia. Long-term decreases in immunological proteins may be caused by uraemia or progressive depletion.