BACKGROUND:Peripheral blood progenitor cell (PBPC) collection has become the main source of hematopoietic cells for high-dose chemotherapy with stem cell rescue and, in some protocols, for allogeneic hematopoietic transplantation. This procedure is complicated in the smallest children because of difficulties related to their weight, and there is little published experience. We have conducted a prospective study to analyze the incidence of adverse events during PBPC collection in the smallest children (< or = 10 kg). METHODS:From January 2000 to November 2005, 257 leukapheresis were performed in our unit, and 13 of them (5%) in 12 children weighing up to 10 kg (median 9 kg, range 5.8-10.9 kg). RESULTS:Most cases had hypovolemic signs during the procedure (usually tachycardia); six cases had hypotension, five of them with pallor and diaphoresis, and, of those, two also had nausea. In all these cases infusion of saline or plasma volume expanders resolved the clinical findings. In two cases the nausea related to hypocalcemia was resolved after calcium gluconate infusion. Changes in platelet counts were also remarkable, with a median platelet loss of 52%. DISCUSSION:Leukapheresis with continuous-flow cell separators has frequent complications related to volume shift in the smallest children. These adverse events are mild and easily resolved with standard measures for hypovolemia, as plasma expander or normal saline infusions. However, we recommend that the procedure should only be performed by teams with extensive experience in the field.