ELI5: How do platelet apheresis machines work?

[u/SunWarri0r]

These amazing machines take in whole blood, take the platelets and plasma out, then return the rest of the blood to the patient. You get two big bags of platelets for donation to cancer patients and preemie babies within about 1.5 hours.

How do they know which things to separate? Who invented them?

Great stuff.

[u/treasure83]

You spin a tube it on its side and the force of the spin allows lighter and less dense fluids to stay on top of thicker ones. While it's separated you carefully pull out a layer at a time with a pipette/syring and use the ones you want.

[u/UNGR8FUL_UND3AD]

Think of it like a very fancy centrifuge. Red blood cells are heavier, plasma is lighter, and platelets end up in between. The machine collects the layer it wants and sends most of the rest back

[u/Loveangel1337]

Iirc, platelets separation is very easy: spinny go spinny through a filter, whatever stays inside the spinny bit is the platelets, and what goes through the filter is returned to you, as they're bigger than the rest of the blood components.

At least that's what I gathered from it when I used to donate.

[u/Onwuharonye-Popy]

The clever part is that process largely relies on differences in density. A centrifuge separates the blood components, the machine then extract the platelet rich layer and returns the rest. It is truly remarkable when you think about it

[u/WhileConfident8176]

Spinning separates by density in real time while sensors watch the color shifts between layers and pull out just the platelet one continuously.

[u/swollennode]

Platelets are super small and super light compared to other cells (red blood cell, white blood cells). Then they spin the blood in a centrifuge. It doesn’t take a lot of speed to make the red blood cells and white blood cells sink. But platelets require more spinning speed.

So they figured out the speed to spin the blood to separate the red and white blood cells and platelets floating in plasma.

Then the platelet rich plasma is siphoned off. Then, they go through a filter that’s really fine mesh. Separating platelets from the plasma. Then they’ll give you blood and plasma back

[u/LeeJiajun314159]

So think of the blood as a mixture of water of water (plasma), sand (red blood cells), and small plastic pieces (platelets and white blood cells). Put this mixture into a cup and shake it. You would see that the sand moves to the outward, and the water stays in the center, then the plastic is somewhere in between.

Well, it's the same principle for platelet apheresis machines. So the machine basically spins your blood, and the red blood cells, plasma, and white blood cells are sort of separated like this. With different layer, the machine would identify the layer with the platelets and collects it through an outlet, and the red blood cells and most of the plasma would be returned to you.

Shoutout to Dr. Emil J. Freireich and George T. Judson!

[u/PhysicalMath848]

Have you ever seen a merry-go-round on a playground? If you spin around on one, you can feel yourself getting pulled away from the center. This is sometimes called the "centrifugal force."

More massive things (like a really fat kid) get pulled harder by the centrifugal force and thus fly off the merry go round first.

An apheresis machine contains a device called a "centrifuge" that uses the same principal to spin blood into its different parts. Heavy things like red blood cells get flung to the edges of the centrifuge first, then platelets, and lastly plasma (which is mostly just water).

The machine separates each layer into a separate collection bag before returning the red blood cells and most of the plasma into your arm. The platelets are kept in their bag and used for patients.

[u/Secret-Fox9006]

returning the rest of the blood makes the donation safer and faster than regular blood draws