Risk of late human immunodeficiency virus type 1 seroconversion in United States soldiers whose initial screening tests were reactive

solution (LISS) and are highly undesirable, because they lead to additional studies that are costly, that waste technologists' time and attention, and that impose unnecessary delays on transfusion. When we became aware of the magnitude of this problem 4 years ago (1 unwanted positive reaction to every 3 clinically significant antibodies in a LISS-IAT, even after the reagents were warmed before mixing2). we decided to use EDTA plasma, instead of serum. We were concerned about the risk of missing those Kidd system antibodies that are detectable in the IAT only by their ability to bind complement, but a review of the literature showed that the phenomenon is very rare with LISS-based techniques. Furthermore, among 11 sera with anti-&' that we had found in the preceding 3 years, the addition of EDTA prevented the IAT reaction in none. We were also concerned about the possibility that group B plasma might fail to detect 4 B units (mislabeled as B) in the IAT of the compatibility test, because of the nonactivation of complement. Each of 20 selected 4 B red cells samples were tested (immediate-spin plus LISS-IAT) with 20 group B serum or plasma samples (a total of 400 double tests). ABO incompatibility was missed in 30 percent of the tests, but there were no differences between serum and plasma. During the last 4 years, in which nearly 100,OOO units of blood have been transfused at our institution, suspected hemolytic reactions were investigated with both semm and plasma. No clinically significant antibody reacting only in serum was found. At the same time, the number of unwanted positive reactions in routine compatibility tests has been reduced by a factor of 10. In addition, and perhaps more important than the increase in specificity of the compatibility test, EDTA samples have been shown to have other advantages. First, only one tube of the patient's blood is needed for all laboratory steps in compatibility testing, which reduces the risk of clerical errors. Second, there are no problems with heparinized samples, as they have been the frequent cause of delays in pretransfusion testing with the increasing use of heparinized catheters in the wards. Third, there is no risk of missing ABO incompatibility because of steric hindrance by activated complement: as is possible when the type and screen is used instead of the complete compatibility test. Fourth, in combination with immediate-spin and LISS-IAT, the use of EDTA samples allows us to provide blood for urgent transfusions, after full compatibility testing, in about 30 minutes. This increases the confidence of surgeons and anesthesiologists in the commitment of the transfusion service and increases overall transfusion safety by reducing requests for noncrossmatched blood. A controlled comparison of plasma and serum that considers all potential advantages and disadvantages, not simply the immunologic ones, would be difficult to perform. The above data do not come from such a study but from an analysis of daily practice. However, we believe that they suggest some advantages of plasma over serum and show that the risk of missing clinically significant complement-binding antibodies is very low. ARTURO ~EREIRA, MD INAKI ALCORTA, MD Service of Hernotherapy and Hemostasis Hospital Clinic0 Villarroel I70 08036 Barcelona Spain