Antibody detection errors due to acidic or unbuffered saline

Isotonic saline solutions, buffered with potassium phosphate or sodium phosphate salts, were evaluated in parallel with unbuffered saline to determine if they improved antibody detection by solid phase red cell adherence or hemagglutination methods. Saline buffered to a pH of 7.0 to 7.5, when used to suspend red cells or to wash sensitized red cells in preparation for the antiglobulin test, produced the best positive solid phase and hemagglutination results. The pH range of commercially prepared blood bank saline (unbuffered) was found to be 5.8 to 6.8, far lower than the desired pH for optimum antibody detection. In the case of solid phase assays employing intact, immobilized reagent red cells, saline with a pH of 7.0 to 7.5 also eliminated falsely positive results due to the dissociation of red cell monolayers from the solid support surface that occurred in the presence of unbuffered or acidic saline. These findings indicate that unbuffered isotonic saline should not be used in solid phase- or hemagglutination-based antibody detection tests. It is recommended that phosphate-buffered saline at a pH of 7.0 to 7.5 be employed.