count in patients with thrombocytopenia [36, 39, 53]. The preservation medium and the size and composition of the storage container make it possible to routinely store platelet concentrates produced by apheresis in a volume of about 200 mL for 5 days [54].
6.3 Erythrocytapheresis
Chronic shortages of certain types of red cells stimulated interest in the use of apheresis to collect the equivalent of two units of red cells from some donors, especially group O. Several instruments are now available for red cell apheresis [30, 31, 36, 38, 39, 55–60] (Table 6.1). After removing RBCs, saline may be infused to the donor to maintain blood volume. The RBCs can be stored in an additive solution for the usual 42 days [30, 36, 39, 59]. The red cell products obtained by apheresis are much more standardized than red cells prepared from whole blood, but otherwise red cells obtained by apheresis have the same characteristics as those produced from whole blood (Table 6.2). The advantages provided by red cell apheresis are to obtain two units of red cells from one donation to allow for fewer donor visits, possible increases in red cell availability, and potentially fewer donor exposures if both units of red cells from one donor are transfused to one patient.
Donors for two‐unit red cell apheresis must meet weight and hemoglobin standards specified for each instrument. Because two units of red cells are removed, they may donate only every 4 months. This is adequate for red cell recovery but may not allow complete regeneration of iron stores [61]. Apheresis for two‐unit red cell collection is taking its place in the mixture of blood component production activities (Table 6.2). Although reactions following RBC collection by apheresis are more common than whole blood donation, almost all reactions were minor and for donors younger than 20 years, reactions are equally common after two RBC collections or a whole blood collection. Thus, two RBC collections are as safe as a whole blood collection [62].
Table 6.2 Comparison of red cell units prepared from whole blood with red cell units prepared by double‐unit red cell apheresis.
| Whole blood | Alyxa | Trima | MCSb | |
|---|---|---|---|---|
| Product volume (mL) | 310 | 301 | 347 | 312 |
| RBC volume (mL) | 190 | 177 | NA | 182 |
| Total hemoglobin (g) | 55 | 57.8 | 60.7 | — |
| Hematocrit (%) | 60 | 58 | 55 | 58 |
| Collection time (min) | 8 | 28 | NA | 50 |
NA, not available; RBC, red blood cell.
a Source: Louie J, Greco BJ, Martinez S. Quality and characteristics of red cells collected on a new automated portable component collection system. Transfusion 2003; 43(Suppl):135A (abstract).
b Source: Smith JW, Gilcher RO. Red blood cells, plasma, and other new apheresis‐derived blood products: improving product quality and donor utilization. Transfus Med Rev 1999; 13:118–123.
6.4 Leukapheresis for the collection of granulocytes
Leukapheresis from an unstimulated donor produced only a marginally adequate dose of granulocytes for therapeutic benefit and never gained widespread use. The resulting blood component is a suspension of granulocytes in plasma prepared by cytapheresis. Early on, patients with chronic myelogenous leukemia (CML) were used as granulocyte donors. However, there were the obvious problems of the use of abnormal or malignant cells, as well as the limited number of patients with CML available to donate. The two additional strategies used to increase the granulocyte yield are the addition of the blood sedimentation agent hydroxyethyl starch (HES) to improve granulocyte separation within the centrifuge and the treatment of donors with corticosteroids, and more recently with G‐CSF, to increase the level of circulating granulocytes.
Leukapheresis procedures in general are usually more complex and lengthier than plateletpheresis. The leukapheresis procedure takes 2–3 hours, compared with about 1 1/2 hours for plateletpheresis, to improve the granulocyte yield. Usually 6,500–8,000 mL of the donor’s blood is processed through the instrument, with removal of about 50% of the granulocytes, resulting in a granulocyte concentrate with a volume of about 200 mL. Because granulocytes do not completely separate from the red cells, granulocyte concentrates usually contain a substantial number of red cells (hematocrit 10% or about 20 mL of red cells); therefore, red cell crossmatching is necessary.
A granulocyte concentrate must contain at least 1 × 1010 granulocytes in at least 75% of the units tested [47]. Neither the American Association of Blood Banks (AABB) Standards nor US Food and Drug Administration regulations specify the number of units that must be tested for quality‐control purposes, but because only a few granulocyte concentrates are prepared by most blood banks, it is customary to test all concentrates.
Hydroxyethyl starch in leukapheresis
The separation between granulocytes from the upper layer of red cells is poor because the density of granulocytes is similar to that of some red cells. Although several agents can be used to sediment red cells in vitro, HES is used because it is licensed in the United States for in vivo use and is not associated with unacceptable reactions or alteration of coagulation tests. The granulocyte yield is doubled when HES is added to the leukapheresis system by constant infusion [63–65]. Several studies of the effects of HES established that the nature and incidence of reactions are acceptable for use on normal donors, the potential for blood volume overload when administered to normal donors can be easily managed during the procedure, there is no adverse effect on laboratory values or platelet or granulocyte function, and there are no adverse long‐term effects. Pentastarch has a shorter in vivo half‐life than HES and can also be used in leukapheresis [66, 67].
Stimulation of donors with corticosteroid or G‐CSF prior to leukapheresis
Another approach to increase the granulocyte yield is to increase the donor’s circulating granulocyte count. Corticosteroids have been the drug of choice, and dexamethasone was selected because it could be given either orally several hours before leukapheresis or parenterally at the beginning of the procedure. Dexamethasone 60 mg can be given orally the evening before, or hydrocortisone 4 mg/m2 can be given intravenously 6–12 hours before leukapheresis. This is a very effective method to increase the granulocyte yield, even more than is accomplished by adding HES to the separation system [64]. It has been suggested that corticosteroids may cause cataracts in