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Maximum donation volumes per session in donor plasmapheresis: reply to Ralf Karger & Volker Kretschmer

Our thanks to Dr Karger and Professor Kretschmer [1] for their valuable comments which, however, contain some points that need clarifying. According to current German national guidelines (GG), donors weighing not less than 50 kg may donate a maximum of 750 ml of plasma (including citrate anticoagulant) per plasmapheresis session [2]. This regulation is not based on the results of our study [3], but is rather the expression of experience gained over a substantial period of time. According to the GG in force between 1996 and 2005 [4], donors were permitted to donate 650 ml of plasma per session (excluding anticoagulant) regardless of body weight, which had to be not less than 50 kg. Most German plasma centres generally considered these 650 ml excluding anticoagulant to equate to 750 ml of plasma including anticoagulant. On the basis of questionable validation studies several plasma centres even came to equate 650 ml of plasma excluding anticoagulant with as much as 815 ml of plasma including citrate. It was to eliminate the confusion about differences between plasma volumes with and without anticoagulant therefore that led more recent GG to limit the amount of plasma collected per session expressly to 750 ml including anticoagulant. Since 1996 at least 8 million plasmapheresis sessions have been performed in Germany without evidence of any increased frequency of circulatory adverse events among donors weighing 50–59 kg. Our prospective findings support this, indicating that neither body weight nor the amounts of plasma donated per kilogram of body weight per session were associated with ceasing from donating for medical reasons, no matter whether related or unrelated to the plasma donations themselves. We did however find an association between dropouts related to medical disorders, low IgG, total serum protein (TSP) or haemoglobin (Hb) levels, and female gender. Our study included 38 females weighing < 56 kg and 117 females weighing 56–60 kg who subsequently donated a total of 2125 and 9747 plasma units, respectively. We observed no severe circulatory adverse events in these donors, but 45 females in all dropped out because of low IgG, TSP, or Hb. Karger and Kretschmer have performed two excellent studies on blood volume regulations in plasmapheresis donors [5,6]. One retrospective analysis included 874 males and 330 females who donated a total of 40 133 plasma units over more than 7 years, which revealed no association between the maximum extracorporeal blood volume during plasmapheresis and circulatory adverse events. The second study of 60 donors showed that up to a maximum of 20%, the extracorporeal volume during plasmapheresis did not reliably predict the degree of hypovolaemic stress. It is difficult to understand why individuals included in these studies should have been donating 650 ml of plasma per session including anticoagulant, which is uncommon in Germany. Therefore, the statement of Karger and Kretschmer that donations of 750 ml of plasma including anticoagulant in donors weighing 50–56 kg clearly increase the risk of symptomatic hypovolaemia is speculative and not based on the evidence. Moreover, the calculations of maximum extracorporeal volumes used in both studies were based on transcapillary refilling rate results derived from small studies and bleeding experiments that cannot be compared with fractionated withdrawal and retransfusion of blood by plasmapheresis. We do, however, agree with Karger and Kretschmer that donor plasmapheresis in accordance with GG and other intensified plasmapheresis guidelines should be studied more extensively with regard to circulatory response and to volume shifts during and after the procedures. But parameters such as transcapillary refilling rate need to be actually determined and not just derived from the literature. Since most, but not all, plasma donors in Germany receive volume replacement at the end of each session the influence of fluid replacement on circulation and volume shifts also remains to be determined.