The pH, conductivity and osmolality of low ionic strength solutions used within the U.K. for the antiglobulin test

Low ionic strength solutions (LISS) for use in the antiglobulin test were obtained from 356 U.K. laboratories. Of the 324 laboratories using LISS to suspend the test red cells and who returned details of their LISS technique, 15 used unequal proportions of red cell suspension and serum despite the LISS being formulated for use with equal proportions. Of the 22 laboratories mixing LISS with serum and red cells suspended in a normal ionic strength medium, four used a LISS preparation formulated for a LISS-suspension technique and three used a commercially available LISS-addition preparation using proportions of red cells, serum and LISS not recommended by the manufacturer. The mean (standard deviation) pH, conductivity and osmolality of the 334 LISS preparations for LISS-suspension was 6.9 (0.2), 4.1 (0.4) mS/cm and 298 (15) mmole/kg, respectively. It is suggested that attention should be paid to the osmolality and, particularly, conductivity during the preparation of LISS because values were observed that were clearly outside the acceptable range cited in the Guidelines for the Blood Transfusion Services in the United Kingdom, i.e. pH 6.7 +/- 0.2, conductivity 3.7 +/- 0.3 mS/cm and osmolality 295 +/- 5 mmole/kg.