Control of the antigen‐antibody ratio in antibody detection/compatibility tests

Abstract

An evaluation was made of the variation and importance of dropper volume delivery on pretransfusion testing in ten hospital transfusion services which annually perform a combined total of 225,000 compatibility tests on the serum of approximately 70,000 patients. The pretransfusion testing by these institutions typifies practices throughout the United States in that serum and red blood cells are used with little awareness of actual volumes used and the resultant proportion of one reactant to the other. Tests of the hospitals' dropper pipettes showed a range of serum delivery per test of 0.0465 to 0.1155 ml. Commercial reagent red blood cell vial droppers delivered (according to cell concentration) from 0.00166 to 0.00294 ml packed red blood cells (pcv). From these findings, it could be shown that the serum to cell ratio in the tests done in two transfusion services was as low as 19 to 1 and that the highest ratio of 70 to 1 was used in only one institution. In none was the serum-cell ratio the optimum of 80 to 1.

Evaluation of the gel system for ABO grouping and D typing

“…Two of the chief deficiencies of the tube agglutination method are the inherent variability of pipetting reactants 3 and the inconsistency in grading the strength of the reactions 4 . The gel assay lends itself to standardization, therefore overcoming the subjectivity of tube testing.…”

The UK National External Quality Assessment Scheme in Blood Group Serology. Compatibility testing 1979-1980: trends and performance in relation to practice in antiglobulin testing

“…The antiglobulin test is used in several major variations and there is little agreement even on important minor variables, such as red cell concentration and serum to cell concentration ratio, which define the sensitivity of the test. Compounding variations of choice, are errors that arise from the lack of precision inherent in the use of such semiquantitative procedures as assessment of cell concentration by eye and of volumes by drop counting (Greendyke et al 1979, Beattie 1980. The present surveys have identified some technical aberrations but most incompatibilities were missed by participants who appeared to be using perfectly acceptable procedures.…”

Blood Grouping Techniques

“…When two drops of serum were added to one drop of cell suspension, the ratio of serum to cells varied from 19:1 to 70:1 (Beattie, 1980). Moreover, the PCV of the red cell suspensions varied by a factor of 2.…”