Albumin Turnover in Peritoneal and Hemodialysis

Abstract

The turnover of albumin is increased in both peritoneal dialysis (PD) and hemodialysis (HD) due to increased external losses, normally leading to compensatory increases in the hepatic albumin synthesis. The normal rate of albumin synthesis is on the order of 12 g/day corresponding to an equally large albumin fractional catabolic rate of ~4% daily. Most albumin catabolism is assumed to occur in the endothelium, but there is also renal and hepatic catabolism and leakage into the gastrointestinal tract. In PD the daily losses are on the order of 5 g/day. There are also external albumin losses in HD, particularly when high-performance membranes are used, the losses per session ranging between 1 and 8 g (or more). The dialytic albumin losses cannot be detected by assessing the transcapillary escape rate of albumin from the plasma compartment to the interstitium. In PD, tracer albumin that has been injected into the peritoneal fluid is absorbed to the tissues surrounding the peritoneal cavity without much edema formation, due to the process of "volume recirculation". A small fraction of the dialysate albumin tracer (0.2-0.3 ml/minute) is directly reabsorbed to the plasma via the lymphatics. A significant portion of dialysis patients are affected by chronic inflammation, such as in the malnutrition inflammation and atherosclerosis syndrome, which is also associated with cardiovascular mortality and fluid overload. These patients usually have a reduced ability to compensate for external losses of albumin, which may result in hypoalbuminemia. Reduced plasma albumin levels in dialysis patients may thus be regarded as a sign of chronic inflammation rather than reflecting malnutrition.