A Stronger Gel Barrier
In horizontal centrifugation, the thickest & most stable gel layer is achieved. In fixed angle centrifugation, the gel barrier layer is formed at a 45-degree angle to the tube and the same volume of gel must seal 40% more surface area than when spun in a horizontal centrifuge.

Post centrifugation, gravity and transportation to the lab encourage the layer to reposition and can break the seal. Remixing of the layers allows the blood to continue to metabolize, negating the positive effects of blood separation within 2 hours from draw and reducing specimen integrity.

Tubes centrifuged in a horizontal centrifuge experience a larger radius, resulting in a higher RCF and more efficient forces. Higher g-forces produce a better seal with the tube wall due to better gel packing. The time required for complete centrifugation is only 2/3 of the time required in a fixed-angle centrifuge.

“When using a fixed-angle centrifuge, and if serum is stored on the gel, visual inspection of the tube is necessary to check for completeness of the barrier due to the fact that the gel has formed at a 45-degree angle and may not provide an adequate seal. Tube manufacturer guidelines for both speed and time should be consulted based on the type of centrifuge used.”

“Barrier formation is more predictable with swing-bucket centrifuges.”

“Tubes should not be re-centrifuged once the barrier has formed. Barriers are more stable when tubes are spun in centrifuges with horizontal (swinging bucket) heads than those with fixed angle heads.”

“Barriers are more stable when tubes are spun in centrifuges with horizontal swing-out rotors rather than those with fixed angle heads.”

NOTE: It is not recommended to re-centrifuge tubes once the barrier has been formed.