A new flow cytometric method for simultaneous measurement of residual platelets and RBCs in plasma: validation and application for QC.

ABSTRACT

BACKGROUND: Guidelines for the preparation of FFP in Austria and Germany require the quantification of residual RBCs in plasma. However, currently there is no validated method for enumeration of RBC counts as low as 1 x 10(9) per L. STUDY DESIGN AND METHODS: A new flow cytometric method was developed for QC, to simultaneously determine if fresh unfrozen plasma contains residual platelets and RBCs. This method uses test tubes (TruCount, Becton Dickinson Immunocytometry Systems) that contain a known number of brightly fluorescent polystyrene beads. Plasma is pipetted into these tubes and mixed with FITC-labeled anti-CD41 and PE-conjugated anti-glycophorin A MoAbs. Acquisition can be performed on a flow cytometer after an incubation period of 15 minutes. RESULTS: Individual standard curves for platelet counts revealed excellent correlation coefficients (r>0.998). Platelet counts were validated against simultaneous measurements by using a cell counter and a hemocytometer. While the flow cytometric method slightly overestimated platelet counts of >40 x 10(9) per L by 10 percent, its precision in the critical range was very good-that is, a deviation of platelets < or = 1 x 10(9) per L from target values, which was even better than microscopic enumeration. The limit of sensitivity was <0.5 x 10(9) per L of platelets. RBC counts were also validated against simultaneous measurements made with a second cell counter. Standard curves for RBC counts also revealed excellent correlation coefficients (r>0.997). The limit of sensitivity was <0.25 x 10(9) RBCs per L. Platelet counts in plasma obtained by plateletpheresis or plasmapheresis ranged from 3 to 60 x 10(9) per L. About 25 percent of all plasma samples had platelet counts greater than the allowed upper limit of 25 x 10(9) per L, while all plasma samples contained fewer RBCs than the upper limit of 6 x 10(9) per L. CONCLUSION: This newly developed method provides a simple, quick, precise, and easily reproducible tool for simultaneous measurement of residual platelets and RBCs in fresh plasma.