Quick facts
- A serum separator tube holds a clot activator and a gel that migrates during centrifugation to separate serum from the clot. The serum is then pipetted or sampled above the barrier.
- The order of draw is the sequence in which tubes are filled from one venipuncture. It exists to stop additives from one tube carrying over into the next, and it is set by CLSI, which publishes the same sequence in both countries.
- Canada and the United States share the same order of draw, so the draw itself does not change at the border. What changes is specimen transport law and the market pathway for the tube itself.
- A detail that clinics routinely miss: CLSI's order of draw guidance states that plastic serum tubes containing a clot activator may cause interference in coagulation testing, and only blood culture tubes, glass nonadditive serum tubes, or plastic serum tubes without a clot activator may be collected before the coagulation tube.
- In the United States a blood specimen collection device is a Class II device under 21 CFR 862.1675, and the regulation names serum separators among the products in that generic type.
A serum separator tube is a blood collection tube containing a clot activator and a separating gel, and it is the tube most routine chemistry panels arrive in. Because the tube is familiar, the rules around it are treated as familiar too. Two laboratories running the same analyser, one in Ontario and one in Ohio, fill the same tubes in the same order, but package and ship the specimen under two different transport regimes. The order of draw is shared; the paperwork is not.
What is a serum separator tube, and what does the gel actually do?
The tube does two jobs at once.
The clot activator shortens the time the blood needs to clot, so the serum can be separated sooner. Without it, the sample sits longer before centrifugation.
The gel is a thixotropic material with a density between serum and clot. During centrifugation it migrates to form a barrier, holding serum above and cells below. That barrier is what lets a laboratory sample serum without disturbing the clot, and it is why the tube must be spun at the specified speed for the specified time. Spin it under-specified and the barrier is incomplete; over-spin a gel tube repeatedly and the barrier can fail.
The important consequence sits upstream of the laboratory. The serum yield and the quality of the barrier depend on how the tube was filled, mixed and stored before it reached the bench. Those are preanalytical steps taken at the clinic, and no downstream instrument can correct them.
What is the order of draw, and where does the serum tube sit?
The CLSI order of draw guidance states the sequence, and the sequence is the same for specimens collected by syringe, by tube holder, or into tubes pre-evacuated at the time of collection.
`` Blood culture tube or bottle → Sodium citrate (light blue) → Serum tubes (red, red-mottled and gold) → Heparin (dark green, light green, green-mottled) → EDTA (lavender, pearl, pink) → Sodium fluoride / potassium oxalate (grey) ``
The serum tube sits third, after coagulation. That position is deliberate, and the CLSI page explains why in the sentence most readers skip past: "Plastic serum tubes containing a clot activator may cause interference in coagulation testing. Only blood culture tubes, glass nonadditive serum tubes, or plastic serum tubes without a clot activator may be collected before the coagulation tube."
That sentence changes a bench habit. If a coagulation tube is drawn at the same visit and the tube before it is a plastic serum tube with a clot activator, the order itself can affect the coagulation result. A laboratory cannot fix it afterwards.
| Step | Tube family | Principal use | Carryover risk if order is wrong |
|---|---|---|---|
| 1 | Blood culture | Microbiology | Contamination from non-sterile tubes |
| 2 | Sodium citrate | Coagulation | Clot activator interferes with coagulation testing |
| 3 | Serum, including SST | Chemistry and serology | Additive carryover into later tubes |
| 4 | Heparin | Some chemistry and special assays | Heparin interferes with several assays |
| 5 | EDTA | Haematology, some molecular work | Chelates calcium, affects coagulation |
| 6 | Fluoride / oxalate | Glucose | Glycolysis inhibition must not leak earlier |
The practical instruction for a draw station is short: put the coagulation tube after the culture and before the serum tube, and do not substitute a plastic clot-activator serum tube into the pre-coagulation position.
Is the way a serum specimen travels different in Canada and the US?
Yes, and this is the sharpest difference between two otherwise identical workflows.
Once a specimen leaves the collection site, it becomes a dangerous good, and each country writes its own rulebook.
Canada. Section 5.16(1) of the Transportation of Dangerous Goods Regulations (SOR/2001-286) provides that a person must not offer for transport, handle or transport dangerous goods included in Category A or Category B of Class 6.2, Infectious Substances, unless the goods are in a means of containment manufactured, selected and used in accordance with CAN/CGSB-43.125. For a Category B shipment the relevant type is Type P650, and the Canadian General Standards Board publishes the packaging standard the regulation points to.
United States. Under 49 CFR 173.199, the same Category B shipment must be in a triple packaging of a primary receptacle, a secondary packaging and a rigid outer packaging. The package must pass a drop test at a height of at least 1.2 m without leakage from the primary receptacle, and must display the UN3373 square-on-point mark with the proper shipping name.
| Item | Canada | United States |
|---|---|---|
| Order of draw | CLSI sequence | CLSI sequence, identical |
| Tube classification | Class II device licence under the Medical Devices Regulations | Class II device under 21 CFR 862.1675 |
| Transport instrument | Transportation of Dangerous Goods Regulations, SOR/2001-286 | 49 CFR Part 173, Subpart E |
| Category B packaging | Means of containment to CAN/CGSB-43.125, Type P650 | Triple packaging, performance-based |
| Drop test | Set by the CGSB standard | 1.2 m, no leakage |
| Marking | Category B mark | UN3373 diamond and proper shipping name |
| Acceptance criteria | Public Health Ontario criteria for specimens sent to PHO laboratories | Receiving laboratory and CLIA requirements |
A Canadian clinic that buys packaging documented only to a US drop test has not automatically bought a Type P650 means of containment, and a US clinic that buys Canadian packaging has not automatically bought a package documented against the 49 CFR drop test.
What makes a serum specimen unacceptable when it reaches the laboratory?
Public Health Ontario's specimen acceptance criteria set out the conditions its laboratories apply, and three of them land hardest on a tube that travels.
Packaging. The specimen packaging must meet the minimum Transportation of Dangerous Goods packaging requirements. That is a Canada-specific hook pointing at a federal statute, and a submission arriving in a plain envelope fails on this clause alone.
Integrity. The specimen must not be leaking. This quietly disqualifies shipments assembled in a hurry, especially where the outer packaging is reused or the absorbent material was left out.
Identity. Containers must carry the patient's full name, or a unique code for anonymous testing, plus a second unique identifier such as date of birth or health card number, the collection date, and the collection time for time-sensitive tests. Where a critical specimen has identifiers that are missing, incomplete or conflicting between the specimen and the requisition, a signed waiver from the submitting health care provider is required before the specimen will be processed and reported. Without it, the test is cancelled.
The failure mode that surprises clinics most is the third. A tube labelled with a short form of a name, or a requisition that disagrees with the label, is a defined trigger for a waiver or a cancellation, regardless of how good the specimen is.
What does a blood draw station actually need on the shelf?
The list is short, but each item carries a specification a buyer should be able to point at.
- Collection tubes, including the serum separator tube. The choice of tube decides the additive and therefore the position in the order of draw.
- Needles and winged sets. A winged infusion set is the usual choice where veins are fragile, and gauge selection belongs to the collector.
- Sharps container. The tube is not the hazard; the needle is. A puncture-resistant container placed within reach is the control.
- Absorbent pad, gauze and tape. For a dressing after the draw and for the trolley surface.
- Specimen containers and transport packaging. Where the specimen is aliquoted or shipped, the packaging has to be documented against the standard that applies.
- Labels and requisitions. The identifier rules are only as good as the label stock and the pre-printed requisition.
Ordering these as one repeat line rather than six separate purchases is what keeps a draw station stocked without a weekly emergency order.
Sources
- CLSI, Order of blood draw tubes and additives
- CLSI, standards programme
- CLSI, about the institute
- 21 CFR 862.1675, Blood specimen collection device
- 21 CFR 880.5570, Hypodermic single lumen needle
- Transportation of Dangerous Goods Regulations, SOR/2001-286
- Medical Devices Regulations, SOR/98-282
- 49 CFR 173.199, Category B infectious substances
- 42 CFR Part 493, Laboratory requirements
- Public Health Ontario, Specimen acceptance criteria
- Public Health Ontario, Test information index
- Public Health Ontario, Kit and test ordering instructions
- FDA, Blood specimen collection device classification
- FDA, Device registration and listing database
- Canadian General Standards Board
- WHO, Laboratory Biosafety Manual, 4th edition
- OSHA, 29 CFR 1910.1030 Bloodborne pathogens
Ordering for a clinic, laboratory or care home? Wholesale and multi-site ordering covers account setup and case pricing, and the B2B wholesale collection lists the lines stocked for institutional buyers. Sites that also run an in-house sterilizer can start with the biological indicator 5-pack trial.
Related reading
- Butterfly needles: gauge selection and sharps rules in Canada and the US
- Does TDG apply to specimen collection in Canada? What clinics must do
- Choosing 95 kPa specimen bags: sizes and absorbent pads
Frequently Asked Questions
What is a serum separator tube used for?
It collects blood for serum-based testing. A clot activator speeds clotting, and a separating gel migrates during centrifugation to hold serum above the clot so the laboratory can sample serum cleanly.
Where does the serum tube go in the order of draw?
Third, after the blood culture tube and the sodium citrate coagulation tube. The position is set by the CLSI sequence, and it is the same in Canada and the United States.
Do Canada and the US use the same order of draw?
Yes. Both follow the CLSI sequence, and the sequence does not change at the border. What does change is the transport law that applies once the specimen leaves the collection site.
Does a plastic serum tube interfere with coagulation testing?
It can. CLSI states that plastic serum tubes containing a clot activator may cause interference in coagulation testing, and that only blood culture tubes, glass nonadditive serum tubes, or plastic serum tubes without a clot activator may be collected before the coagulation tube.
How is a serum specimen packaged for shipment in Canada?
As a Category B infectious substance, under the Transportation of Dangerous Goods Regulations, in a means of containment manufactured, selected and used in accordance with CAN/CGSB-43.125, with Type P650 packaging for the Category B case.
How is the same shipment packaged in the United States?
As triple packaging of a primary receptacle, a secondary packaging and a rigid outer packaging, able to pass a drop test at a height of at least 1.2 m without leakage, marked with the UN3373 square-on-point mark and the proper shipping name.
Why would a serum specimen be rejected by the laboratory?
Three reasons carry most of the weight: packaging below the federal transport minimum, a leaking specimen, and identifier failure. Where identifiers are missing, incomplete or conflicting between specimen and requisition on a critical specimen, a signed waiver from the submitting provider is required, and without it the test is cancelled.
CliniEco Medical supplies specimen containers, transport packaging, needles, sharps containers, gloves and the wider laboratory consumable lines described in this article. Health Canada MDEL #35334. This article is written for laboratory, clinic and procurement professionals and is not clinical guidance; collection technique and acceptance decisions belong to the collecting and receiving laboratory.
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