Diagram: butterfly blood collection set with holder, next to it a discard tube and a PRP tube filled to the fill mark

Blood collection for PRP: tourniquet, filling and inverting PRP tubes correctly

Blood collection · Pre-analytics for PRP and PRF

By the time the centrifuge starts, part of the work is already done, or has already gone wrong. How long the tourniquet stayed on, whether the PRP tube is full and how it was mixed all help decide whether the protocol works the way it is meant to. The key steps are quick to learn and easy to set down as a team routine.

Reading time approx. 8 minutes · Updated: October 2026

Why the blood draw matters

Vi PRP-PRO contains 0.8 ml of sodium citrate for about 9 ml of blood. That ratio is only right if the tube fills as far as intended. If it stays half empty, each millilitre of blood meets more citrate than planned. With Density for PRF without anticoagulant, something else counts: clotting begins at the moment of collection, so the time until the centrifuge starts matters most.

The rules for clean blood collection come from laboratory medicine, where a mistake means a wrong result. The European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) and the Latin American confederation COLABIOCLI have described them step by step.[1] Many of these principles can be transferred to blood collection for PRP, especially with vacuum tubes containing an anticoagulant. The instructions for use of the respective PRP system and the work instructions of your facility remain authoritative.

Before the puncture: patient, label, materials

Identify first. Ask the patient to state their name and date of birth rather than reading the name out, and check the details against your records.[1] When the preparation goes back to the same person, this is not a formality. That is why you work with only one patient at a time.

Label at the patient. Tubes are labelled or identified in the presence of the patient. Whether this happens before or straight after collection is decided by each facility on the basis of a risk analysis.[1] What matters is that no unlabelled tube leaves the room.

Everything within reach. Blood collection set with holder, PRP or PRF tubes, a discard tube if needed, tourniquet, skin disinfectant, swabs and plaster. Keep the sharps container within arm’s reach.[1] A tube rack keeps the filled tubes upright until they go into the rotor.

For PRF, set everything up beforehand. The Density manufacturer documentation specifies that centrifugation starts within 60 seconds of collection. Rotor, counterweight and programme are therefore set before you puncture. More on this in our article Vi PRP-PRO or Density.

Which set? Butterfly with holder

With vacuum PRP tubes, blood is led into the tube via a holder. A butterfly set with wings and tubing is easy to guide and secure, even with narrow veins. Its tubing has one peculiarity, though: it is filled with air at the moment of puncture. What that means for the first tube is explained further down.

VACUETTE® EVOPROTECTVACUETTE® SAFETYBD Vacutainer® Safety-Lok™
Needle21G, 0.8 × 19 mm21G, 0.8 × 19 mm21G, 0.8 × 19 mm
Tubing30 cm19 cm17.8 cm
Holderpre-attachedpre-attachednot included
Pack1 or 30 pcs35 pcs1 or 50 pcs
Special featurelongest tubing, more distance to the tube changecompact, short tubingsupplied without holder

The overview compares the sets with one another. It is not a compatibility confirmation by the manufacturers: whether set, holder and tube are used together is to be checked against the current instructions for use of each product.

The blood draw step by step

  1. Apply the tourniquet briefly, not too tight

    Place the tourniquet about one hand width above the puncture site, tight enough to stop venous return but not arterial inflow.[1] The fist stays open, no pumping.[1]

  2. Disinfect and let dry

    Disinfect the skin according to your hygiene plan, wipe in one stroke and let it dry. Do not touch the site again afterwards.[1]

  3. Puncture, with a butterfly discard first

    If the PRP tube is the first or only tube and depends on its intended fill volume, as tubes with a pre-filled anticoagulant do, a discard tube without additive goes into the holder of a butterfly set first.[1][2]

  4. Release the tourniquet as soon as blood flows

    The tourniquet comes off as soon as blood runs into the first tube, after one minute at the latest.[1][2] Longer stasis changes the composition of the sample.[3]

  5. Let the tube fill completely

    Hold the tube in the holder with your thumb until the vacuum is exhausted and no more blood flows in.[2] Do not remove it early.

  6. Invert straight away

    Invert gently immediately after filling, 7 times for Vi PRP-PRO according to its instructions for use. Inverting means turning the tube slowly upside down and back. Avoid vigorous shaking.[1] For Density, its manufacturer documentation applies.

  7. Secure the needle, care for the site

    Activate the safety mechanism and dispose of the needle in the sharps container immediately.[1][4] Apply a swab, keep the arm straight and do not bend it.[1]

  8. Promptly to the centrifuge

    Tubes upright in the tube rack, then straight into the rotor, loaded symmetrically. From here the protocol of the tube applies, for Vi PRP-PRO 1200 × g for 7 minutes.

Several tubes from one puncture? If you also fill laboratory tubes, the defined order of draw applies: blood culture, citrate, serum, heparin, EDTA, glycolysis inhibitor.[1] Citrate tubes such as Vi PRP-PRO therefore come early, so no additives from other tubes get into them.

Why the first butterfly tube does not count

The tubing of a butterfly set is filled with air before the puncture. When the first tube is in the holder, the vacuum draws this air first. Less vacuum is left for the blood, and the tube is underfilled. In a tube with a pre-filled anticoagulant, the ratio is then no longer right.[1]

Air in the tubingtarget fillunderfilledPRP tubeas the first tube
Without a discard tubeThe air in the tubing takes up part of the vacuum. The first tube does not reach its intended fill.
Tubing filled with bloodtarget fill1  Discardno additive2  PRP tubefull draw
With a discard tubeA tube without additive takes up the air. The PRP tube that follows fills to its intended level.

Schematic illustration.

The recommendation of European laboratory medicine is clear: if a citrate coagulation tube is the first or only tube on a butterfly set, a discard tube is collected beforehand. With a straight needle this is not necessary.[1] The instructions for use of the VACUETTE® EVOPROTECT butterfly set also provide for a discard tube without additive when the test is sensitive to underfilling.[2] For PRP tubes, the instructions for use of the respective tube apply.

Five mistakes the tube does not forgive

  1. Tourniquet on too long, fist pumped

    Stasis of more than one minute and pumping the fist change the sample before the first drop.[1][3] Release the tourniquet as soon as blood flows.

  2. Tube removed too early

    A tube that has not filled completely has a different mixing ratio. For diagnostic vacuum tubes, the EFLM strongly advises against filling below 90 % of the intended volume.[1] For PRP tubes, the target fill specified by the respective manufacturer is authoritative.

  3. Discard tube forgotten

    On a butterfly set without a discard tube, the first tube does not fill completely. A tube without additive costs a few seconds.

  4. Shaken, or not mixed at all

    Without mixing, the citrate does not spread through the blood. Vigorous shaking, on the other hand, can damage blood cells and cause haemolysis.[1] The answer lies in between: invert gently and immediately, as often as the instructions for use specify.

  5. Not assigned at the patient, several patients in parallel

    An unlabelled tube in the rack is a mix-up risk. Assigning tubes in the presence of the patient and one patient after another reduce it considerably.[1]

How such mistakes can show up after centrifugation, for example as reddish plasma or strands in the tube, is described in the article Troubleshooting PRP and PRF.

Checklist for the treatment room

To print out and adapt to your own work instructions:

Before

  • Patient actively identified, name and date of birth checked
  • Tube expiry dates checked
  • Set with holder, discard tube, tourniquet, disinfectant, swabs and sharps container ready
  • For PRF: centrifuge prepared with rotor, counterweight and programme

During collection

  • Tourniquet one hand width above the site, fist open
  • Disinfectant dry, site not touched again
  • With a butterfly: discard tube without additive first
  • Tourniquet released as soon as blood flows, after 1 minute at the latest
  • Tube filled completely, inverted gently straight away (Vi PRP-PRO: 7 times)

After

  • Safety mechanism activated, needle in the sharps container
  • Swab applied, arm straight
  • All tubes labelled or assigned in the presence of the patient
  • Tubes upright in the rack, promptly to the centrifuge

Frequently asked questions

Do I need a discard tube for every blood draw?

No. The recommendation applies to butterfly sets when a citrate tube is the first or only tube. With a straight needle, no discard tube is needed.[1]

Which tube do I use as the discard tube?

A tube without additive that fits your holder.[2] It takes up the air from the tubing, and its contents are discarded.

What if the PRP tube does not fill completely?

Find the cause first: often the discard tube is missing, the needle is resting against the vein wall, or the vacuum is no longer complete, for example after the expiry date. For diagnostic vacuum tubes, the EFLM advises against filling below 90 %.[1] Whether an underfilled PRP tube can be used is governed by the information from the tube manufacturer.

How often must a PRP tube be inverted?

As often as the instructions for use of the tube specify. For Vi PRP-PRO it is 7 gentle inversions immediately after collection. In general: invert gently, do not shake.[1]

How long may the tourniquet stay on?

Up to one minute in total. It is released as soon as blood flows into the first tube.[1]

What needle size do the sets have?

All three blood collection sets at prplab have a 21G needle measuring 0.8 × 19 mm. They differ in tubing length, holder and pack size.

The products

Sources

  1. Simundic AM, Bölenius K, Cadamuro J, et al. Joint EFLM-COLABIOCLI Recommendation for venous blood sampling. Clin Chem Lab Med. 2018;56(12):2015–2038. doi:10.1515/cclm-2018-0602
  2. Greiner Bio-One: instructions for use VACUETTE® EVOPROTECT safety blood collection set, 980274 Rev02, 06-2025. gbo.com
  3. Lippi G, Salvagno GL, Montagnana M, Brocco G, Guidi GC. Influence of short-term venous stasis on clinical chemistry testing. Clin Chem Lab Med. 2005;43(8):869–875. doi:10.1515/CCLM.2005.146
  4. Council Directive 2010/32/EU implementing the Framework Agreement on prevention from sharp injuries in the hospital and healthcare sector. eur-lex.europa.eu/eli/dir/2010/32/oj

Product information: instructions for use Vi PRP-PRO (D-BIOTECH S.R.L.S., Catania), product documentation Density (Xenoderm Srl). VACUETTE® is a trademark of Greiner Bio-One GmbH; BD Vacutainer® and Safety-Lok™ are trademarks of Becton, Dickinson and Company.

Note for professional users: This article summarises recognised recommendations on venous blood collection and manufacturers' information. It does not replace the instructions for use of the blood collection set and the tubes, nor the hygiene plan and work instructions of your facility. Blood collection is performed by qualified professionals.

Exclusively for medical professionals.

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