Novel use of the BD FACS SPA to automate custom monoclonal antibody panel preparations for immunophenotyping

The effective and accurate diagnosis of hematologic malignancies relies on flow cytometric immunophenotyping. Selected combinations of monoclonal antibodies (mAbs) arranged in multicolor panels allow for the accurate definition of normal and abnormal hematologic cell populations. The most time-consuming and crucial step in the staining process involves dispensing combinations of multiple mAbs into their appropriate staining tubes. This step is prone to error, requires concentration and accuracy, and is dependent on technologist experience. The Becton Dickinson BioScience (BD) FACS Sample Prep Assistant (SPA) is touted as a breakthrough in automated in vitro diagnostic sample preparation. The SPA is designed to automate BD MultiTESk and BD TriTest lyse/no-wash assays. However, because most cases in our laboratory require tedious application of unique four-color mAb cocktails for leukemia and lymphoma testing, we wondered whether the SPA would be helpful in accurately dispensing these mixtures.

The mAb panels were prepared by the SPA in two separate timed runs and on separate days. Eleven specimens (nine from patients and two from normal volunteers) were split and stained with four-color cocktails created by the SPA or manually. The percentage of positive (%P) cells and mean fluorescent intensity for each mAb pair were determined. These values were plotted against each other and correlation values were calculated. To quantitate timesaving in the laboratory, two technologists prepared individually the same mAb panels and were timed.

The correlation between the two methods was high; r(2) was 0.988 for 158 %P antigen pairs; no bias between the manual and robotic methods was detected with the Wilcoxon rank test. Bland-Altman analysis indicated no obvious relation between the difference and the mean of %P cells, suggesting that the SPA successfully dispensed antibodies for leukemia/lymphoma panels. The two methods may be interchangeable, although the limited sample size prohibits this conclusion from Bland-Altman statistics alone. In addition, one possible error was detected in the SPA-prepared panels. The SPA averaged 65 min/run, the experienced technologist 12.95 min/run, and the inexperienced technologist 54.9 min/run.

SPA dispensing time was twice the average manual dispensing time; however, SPA use was completely automated and freed the technologist to perform other tasks. SPA use permitted preemptive preparation of mAb panels and thus streamlined processing; however, the cost of the assay and the amount of reagent waste increased. It is certain that software modifications by BD could decrease the SPA reagent dispense time and decrease the cost associated with reagent waste when the SPA is used in this novel fashion.