Even in a mobilized patient, the number of stem cells circulating in the entire blood volume may be inadequate to provide engraftment; thus, processing of multiple blood volumes, often over more than 1 day, is required for some patients (Rowley et al. 2001). This is typical for patients who have been extensively pre-treated with chemotherapy. The minimum required for most patients is one large-volume leuka-pheresis (LVL), which represents approximately 201 in an adult or three to four blood volumes in a child. This volume is a typical goal for a single apheresis session, although some physicians will pherese for a total of six or more blood volumes.

There are two issues in PBSC collection that require special consideration in children. First is the issue of priming. Even using devices that minimize ex-tracorporeal volume, smaller children require priming of the apheresis machine with red cells. This prevents unacceptable dilutional anemia. Second is the issue of anticoagulation. In older patients, anticoagulation required for the apheresis procedure is accomplished using ACD. Although rapidly reversible, ACD creates a higher risk of symptomatic hypocalcemia in young patients. These patients are managed with a combination of ACD and heparin to achieve anticoagulation, or receive a calcium infusion in the apheresis return line.

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