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Glossary

Stokes' law

Stokes' law describes how fast a particle sediments through a fluid under force. In blood separation it governs why erythrocytes, leukocytes, and platelets settle at different rates, and therefore why centrifugation separates them at all.

Figure

The density gap

DENSITY · KG PER CUBIC METRE Plasma 1,025 Platelets 1,040 to 1,060 Leukocytes 1,050 to 1,085 Erythrocytes 1,090 to 1,100 Denser fractions sediment faster. That gap is the entire basis of separation.

Figure. Sedimentation speed depends on the density difference between a cell and the surrounding plasma. This is why a more expensive centrifuge does not change the sedimentation rate of a platelet.

In practice

The practical consequence is that platelet yield is bounded by physics rather than by machine price. A more expensive centrifuge does not change the sedimentation rate of a platelet.

See also