The search phrase "vacuum tubes with sodium citrate" covers two different purchases. A laboratory is looking for tubes for coagulation tests and ESR, while a clinic that performs PRP therapy is looking for tubes to prepare plasma. From the outside the products look alike: a glass or plastic body, vacuum, a citrate solution inside, often the same blue cap. In substance they are different medical devices with different registration and different requirements. Here is the difference, and why a laboratory tube must not be used for PRP.
Why there is sodium citrate in the tube
Blood outside a vessel clots within minutes. To prevent this, an anticoagulant is placed in the tube in advance. Sodium citrate reversibly binds calcium ions, without which the clotting cascade does not start. The word "reversibly" is the key: add calcium back and clotting resumes. That is why citrate is used both in the laboratory, where coagulation parameters are measured on restored clotting, and in PRP, where activation of the plasma, if the protocol calls for it, is done in the syringe.
Heparin works differently: it blocks thrombin and does not let clotting resume. That suits some laboratory tests, but not PRP. More in the article on heparin and sodium citrate.
The laboratory citrate tube: what it is for
Tubes for laboratory tests are in vitro diagnostic devices: the contents are analysed and discarded and never return to the patient. Hence the requirements: an exact citrate dose for the blood volume, a stable solution, a clean inner surface. Two typical variants:
- Blue cap, sodium citrate 3.2 % (or 3.8 %) at a 9:1 ratio. Coagulation panel: prothrombin time, INR, APTT, fibrinogen. The tube is filled exactly to the mark, otherwise the ratio shifts and the result is distorted.
- Black cap, sodium citrate at a 4:1 ratio. Erythrocyte sedimentation rate by the Westergren method.
Such a tube does not have to be sterile inside in the sense required for devices that contact patient tissue. Its citrate solution is not tested for pyrogens, there is no separating gel, and the volume is chosen for the analytical task, not for plasma yield.
The PRP tube: what is different
In PRP therapy blood is centrifuged and the resulting plasma is injected into the patient: into a joint, into the skin, into an implant site. Everything that was in the tube ends up in the body. That is why a PRP tube is registered as a class 2b medical device and its contents are held to the standard of something that enters the body:
- Sterile and pyrogen-free contents. The citrate solution and the gel are tested not only for purity but for the absence of pyrogens, otherwise a reaction after the injection is possible.
- Separating gel. After centrifugation it forms a barrier between the plasma and the cellular fraction: the physician draws plasma above the gel without touching the red and white cells.
- A body built for the centrifuge. The glass is rated for PRP centrifugation, the walls do not crack and do not shed particles.
- A citrate dose matched to 8 ml and to plasma yield rather than to coagulation parameters.
- A registration certificate whose intended use is the preparation of platelet-rich plasma. This is what an inspector asks for at a clinic.
More on device classes in the article on safety class 2b.
Side by side
| Feature | Laboratory citrate tube | ReLife PRP tube |
|---|---|---|
| Purpose | Coagulation tests, ESR | Plasma for injection into the patient |
| Registration | In vitro diagnostic device | Class 2b medical device, Registration certificate RK-MP-5№016078 |
| What happens to the contents | Analysed and discarded | Injected into the patient |
| Sterile, pyrogen-free contents | Not required | Mandatory |
| Separating gel | No | Yes |
| Volume | 1.8 ml, 2.7 ml, 4.5 ml | 8 ml |
| Cap | Blue or black | Blue |
| Price | Noticeably lower: a simpler device without class 2b testing | 800 KZT per tube |
Can a laboratory tube be used for PRP
Technically the blood will not clot in it either, and it will separate after centrifugation. But the clinic takes on three problems.
- Legal. The device is used outside the intended use in its registration certificate. At an inspection, or if a patient has a complication, the clinic answers for it, not the tube manufacturer.
- Clinical. Nobody guarantees that the solution going into a joint or the skin is pyrogen-free. Without gel, part of the red and white cells is drawn into the syringe with the plasma, and that means pain and inflammation after the injection.
- Practical. A 2.7 or 4.5 ml volume yields too little plasma, so several tubes have to be pooled, which adds handling steps and contamination risk.
The saving on the tube is a few hundred tenge per procedure. The procedure itself costs the patient an order of magnitude more, and a single complication costs more than a year of such savings.
What to check on the label when buying
- Intended use and safety class in the registration certificate. The certificate number can be checked in the Kazakhstan medical device register.
- The words "sterile" and "pyrogen-free" on the pack, and the sterilisation method.
- Separating gel, tube volume, type of anticoagulant.
- Lot number and expiry date on every tube or pouch.
- An individual sterile pouch for every tube.
The ReLife tube
ReLife PRP 8 ml vacuum tube: glass, sodium citrate, separating gel, blue cap, individual sterile pouch. Registered in Kazakhstan as a class 2b medical device (Registration certificate RK-MP-5№016078). Price 800 KZT per tube, and for clinics with regular use there is the PRP BOX of 25 tubes. Delivery across Kazakhstan and the CIS, payment on receipt.
If you are choosing between several brands of PRP tubes, see the checklist for choosing PRP tubes for your clinic.