Cellular sedimentation and barrier formation under centrifugal force in blood collection tubes

Abstract

We have studied and detailed cell sedimentation and gel movement in clotted and anticoagulated blood during centrifugation of BD Vacutainer™ tubes using recommended handling conditions. Using a strobe centrifuge and video camera, we showed that the dynamics of cell and gel movement are different for clotted and anticoagulated blood. In BD SST tubes, the gel must move around the clot. The gel flows continuously along the tube wall, delaying its arrival at the interface between the serum and cells. The benefits of this delay are that the serum is clarified prior to barrier formation, and few cells are entrapped in the gel, allowing for improved serum quality. In plasma tubes, cells sediment more slowly than in serum tubes due to several factors. In BD PST tubes, the gel can move readily through the anticoagulated blood to reach the plasma: cell interface. Unlike the gel moving in a continuous flow in BD SST tubes, the gel in BD PST tubes moves in discrete pieces. Because the gel reaches the interface faster and travels through the blood, more cells are trapped between the gel portions and concentrate at the interface. Most of these cells sediment through the gel during the remaining centrifugation period. Reducing the overall TAT of reporting test results is a common clinical laboratory quality measure. Frequently, reducing the processing time is a method to achieve shorter TAT. However, as demonstrated by our studies, specimen purity is dependent upon cell separation and gel movement (in a tube containing gel). This is particularly true for plasma samples as cell sedimentation takes much longer for anticoagulated blood than clotted blood. Although cell sedimentation times, and thereby, centrifugation times, can be shortened with serum tubes, clotting time is critical to obtaining a cell-free and fibrin-free serum. Use of lithium heparin tubes greatly reduces the total TAT, but shortened centrifugation times may result in a supernatant containing some cells. Some reductions in processing time of blood collection tubes can be made without compromising specimen quality depending on the type of tube collected. Gel tubes can significantly improve serum/plasma purity by separating the cells from the supernatant. The gel barrier also permits primary tube sampling without cellular contamination, thus improving laboratory efficiency.