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 (D/P). These ratios were not significantly changed suggesting that permeability remained constant. However, there was a trend for beta 2-microglobulin, creatinine, and urea to increase progressively. After 56 weeks, beta 2-microglobulin had increased from 27.9 to 31.3 mg/L (p less than 0.05) and creatinine 1006 to 1099 mumoL/L (p less than 0.05) and both correlated with time on CAPD (p less than 0.001). Plasma alpha 1-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 less than 0.001 for all). It is concluded that increases in beta 2-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.

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