How to choose a PRP centrifuge
Nearly all published guidance on centrifuge selection comes from the people selling the centrifuge, and it tends to lead with whichever specification flatters the machine. Three things actually determine whether a given unit can run the protocols you intend to use.
Select on relative centrifugal force, not RPM. RCF is the force the sample actually experiences, and it is the figure a spin protocol specifies. Because RCF depends on rotor radius as well as speed, two machines set to the same RPM do not deliver the same force.
Alignment chart: radius, speed, relative centrifugal force
Second-spin band. Concentrates platelets from plasma already separated.
Plate I. The three scales are placed so that a straightedge laid across rotor radius and rotor speed crosses the third axis at the resulting force, following RCF = 1.118 × 10−5 · r · N², r in centimetres. Shaded regions mark the bands most protocols sit in. This is the chart, not a picture of one.
Force, not speed
RPM is a property of the motor. RCF is a property of the sample. A protocol paper specifies the second, a spec sheet advertises the first, and the two are related only through the radius of the rotor doing the spinning.1
The consequence shows up as a yield problem. Two clinics believe they are running the same published protocol, both set their machines to the same RPM, and get different platelet concentrations. Neither has done anything wrong at the bench. They own rotors of different radius, so the same speed delivered materially different force.
Drag Plate I with a 6 cm rotor, then again at 16 cm without touching the speed. The force roughly triples. That is the entire argument, and it is why rotor radius belongs on the purchase order rather than in a manual nobody opens.
It gets worse before it gets better. There is no single RCF inside a tube at all.2 Force grows with distance from the axis, so the sample at the bottom of the tube experiences more of it than the sample at the top. When a paper or a spec sheet says 400 g, the honest question is: measured where?
What settles it
Ask for the RCF range at the rotor radius shipped with the unit, and ask which radius the figure was taken at. Not the maximum anywhere in the product line. Those are different numbers, and only one of them describes the machine arriving at the clinic.
What a protocol has to specify
In 2021 a systematic review gathered every PRF centrifugation protocol it could find in the literature. It found 121 eligible studies, 29 different protocols, and 16 different machines. Fixed-angle rotors ranged from 33 to 45 degrees. Radius-max ranged from 85 to 130 mm. Speeds were reported anywhere from 700 to 3,500 RPM, and forces from 44 to 1,000 g. Its conclusion was that protocol reporting is not standardised at all.3
That is the whole problem stated in one paragraph, by someone who counted. A protocol published as 3,000 RPM for 10 minutes is not a protocol. It is a fragment of one, and it cannot be reproduced by anybody who does not happen to own the same machine.
The same review proposed a fix, an acronym for the six things a protocol must state before anyone else can run it. Very little of the equipment marketing you will read has ever heard of it.
AR2T3, and the range found across the literature
| Parameter | Reported range, 121 studies | |
|---|---|---|
| A | Angle of the rotor | 33° to 45°, fixed-angle |
| R | Radius-max, axis to tube bottom | 85 to 130 mm |
| R | RPM, and the RCF it produces | 700–3,500 rpm · 44–1,000 g |
| T | Time of centrifugation | varied |
| T | Tube size | varied |
| T | Tube characteristics | glass, plastic, titanium |
Two of the six are properties of the machine you are buying, and cannot be changed afterwards: the rotor angle and the radius. That is why they belong in the purchasing decision rather than in the operating manual.
One spin or two
The first spin separates plasma from red cells. A second spin concentrates the platelets already suspended in that plasma. Concentration factor comes almost entirely from the second spin, and so does the risk of damaging the platelets you went to the trouble of collecting.4
Named protocols, as actually reported in the source literature
| Protocol | Reported force | Time | Note |
|---|---|---|---|
| L‑PRF, original | 408 g at the clot 653 g max · 326 g min | 12 min | Radius to clot stated as 50 mm. The three figures are the same spin.5 |
| i‑PRF, low-speed concept | 44 to 177 g | 3–8 min | Lower force raised platelet, leukocyte and growth-factor counts against a 710 g comparator.6 |
| PRF, across the literature | 44 to 1,000 g | varied | 29 distinct protocols, 16 machines, no standard.3 |
Note what the low-speed work implies. Harder is not better. Above a certain force you are not concentrating platelets, you are sedimenting and damaging them, and the literature keeps finding that the sweet spot is lower than the equipment can reach.
Note also the L‑PRF row. Solid PRF protocols specify a horizontal rotor, and that one line rules out a large share of the compact benchtop units marketed for PRP work. Better to know it before the purchase order than after.7
Fixed-angle or swing-out
A fixed-angle rotor holds the tubes at a set inclination. Across the reviewed literature that angle runs from 33 to 45 degrees, and it is fixed in the sense that matters most: you cannot change it after the machine is on the bench.3 It is compact, it reaches higher speeds, and the layers settle against the tube wall on a slant.
The slant is the working problem. The buffy coat forms as a diagonal band rather than a flat one, and drawing it cleanly without pulling red cells takes a steadier hand and more repetition to learn. Two technicians will not necessarily produce the same draw from the same tube.
A swing-out rotor lets the tubes rotate to horizontal under load, so the layers stratify flat and perpendicular to the tube. The draw is easier and, more usefully, more repeatable across staff. The tradeoff is footprint and top speed.
Which one
If solid PRF is in scope, the decision is already made. If the clinic runs liquid PRP only and one experienced person performs every draw, a fixed-angle unit is workable. If several people will run the same protocol and the output has to be identical regardless of who is at the bench, buy the swing-out and give up the counter space.
Six questions for the demo
Take these to the vendor. A representative who cannot answer the first three from memory is selling a box rather than an instrument.
What is the RCF range at the rotor radius shipped with this unit, and at which radius is that figure measured?
Not the maximum across the product line. This unit, this rotor, and state whether the figure is RCF-max, RCF-min, or an average. All three are different numbers for the same spin.Does the panel set and report RCF, or only RPM?
An RPM-only panel means a hand conversion at every protocol change, which is a staff error waiting for a busy morning.Fixed-angle or swing-out, what angle, and what is radius-max in millimetres?
Angle and radius are two of the six parameters a protocol needs (Table 1), and neither can be changed after purchase. If the rep has to go and look them up, that is itself an answer.Which kits and tube geometries is this rotor validated against?
Bore and tube dimensions have to match. This is where a cheap unit quietly becomes an expensive one.What does a procedure cost in disposables?
The unit price is the small number. The kit price multiplied by annual volume is the real one.How long is a full cycle, including load and unload?
Throughput is a room-scheduling constraint, not a line on a spec sheet.
Questions
Does a more expensive centrifuge produce better PRP?
Not by itself. Yield is set by the spin protocol, the tube and anticoagulant, and the draw. A more expensive unit buys programmability, throughput, and repeatability, which begin to matter once more than one person runs the protocol and the output has to be the same every time.
Should I buy a fixed-angle or swing-out rotor?
Fixed-angle rotors are compact and reach higher speeds, but the layers settle against the tube wall on a slant, which makes a clean draw harder. Swing-out rotors bring the tube horizontal so the layers stratify flat. Solid PRF protocols specify a horizontal rotor, so if PRF is in scope the question is settled before it is asked.
Can I run a published PRP protocol on any centrifuge?
Only if the machine can reach the specified g-force. A protocol specifies RCF, and converting RCF to RPM requires the radius of your particular rotor. Two machines at the same RPM apply different force when their rotor radii differ. Plate I will tell you in a few seconds whether a given machine can reach a given band.
The three specifications that decide whether a protocol is runnable at all on the machine you are about to buy.
References
Figures in Tables 1 and 2 are taken from these sources and are reproduced as reported, not as recommendations.
- Herrera-Vizcaino C. Systematic review of platelet-rich fibrin (PRF) centrifugation protocols in oral and maxillofacial surgery and the introduction of AR2T3: an easy to remember acronym to correctly report vertical and horizontal PRF centrifugation. Frontiers of Oral and Maxillofacial Medicine, 2021. doi:10.21037/fomm-21-40 Source for the AR2T3 parameters, the 121-study count, the 33°–45° rotor-angle range, the 85–130 mm radius range, and the 44–1,000 g force range.
- Miron RJ, Chai J, Zheng S, et al. Impact of g force and timing on the characteristics of platelet-rich fibrin matrices. Scientific Reports, 2021. doi:10.1038/s41598-021-85736-y Source for the original L‑PRF protocol figures, including the distinction between RCF at the clot, RCF-max, and RCF-min.
- Choukroun J, Ghanaati S. Reduction of relative centrifugation force within injectable platelet-rich-fibrin (PRF) concentrates advances patients' own inflammatory cells, platelets and growth factors: the first introduction to the low speed centrifugation concept. European Journal of Trauma and Emergency Surgery, 2018. doi:10.1007/s00068-017-0767-9 Source for the low-speed centrifugation concept and the 710 g, 177 g, and 44 g protocol comparison.
Where our reading of a source is contested, or where you believe a figure here is wrong, we would rather know. Corrections are made in place and the revision date at the head of this bulletin changes when they are.