Prediction of reduction in predialysis concentrations due to interdialysis weight gain

There is little quantitative information about the influence of weight change before and during hemodialysis on the concentration of proteins, lipoproteins, lipids, enzymes and other dialysis-resistant compounds in blood. We studied the concentration of 12 such compounds before and at the end of high-flux hemodialyses, 1.5 h after the start and 1, 2 and 3 h postdialysis and have developed formulae for roughly predicting the near steady-state 2-3 h postdialysis concentration. For hemoglobin, albumin, total protein and total cholesterol, the relationship of mean change in concentration to weight loss in groups was linear, and the % increase in concentration correlation correlated with % weight reduction (r = 0.64-0.81 and p = 0.002-0.0002). Correlations with ultrafiltration rate were comparable. By 3 h postdialysis values were relatively stable; the average fall in concentration for theses 4 compounds was 25% from end dialysis. The simplest formula we found which roughly predicts the % increase in concentration from predialysis to 3 h postdialysis is to multiply the % loss in body weight in kg during dialysis by 3.3. More accurate formulae were developed using combined and specific regression equations relating % weight loss during dialysis to % concentration rise. Mean values for alkaline phosphatase, triglycerides, lipoprotein (a), high-density lipoprotein cholesterol, calcium, apolipoprotein B, bilirubin and aspartate aminotransferase also rose appreciably during dialysis with significant increases for the first five. With major interdialytic weight gain, the reduction in predialysis concentrations of hemoglobin and cholesterol may be enough to inappropriately modify treatment decisions about anemia (e.g. erythropoietin) or hypercholesterolemia, and to cause false concern about the concentration of albumin for nutrition and prognosis. Major weight gain may also contribute to concentration changes in numerous other compounds resistant to dialysis.