Written and maintained by CASRAI Editorial Board
Last updated
Coagulation tubes are blood collection tubes used to collect specimens for plasma-based clotting tests; the manufacturer example on this page is a light blue-closure tube containing buffered 3.2% sodium citrate. This page is a product-class overview for clinic staff, buyers and students: what the class is, what a manufacturer specification looks like, and what to check on the tube and its documents before it is stocked.
This page describes products and general use; it is not medical advice.
For the additive chemistry, fill ratio and sizes in depth, read the blue top tube additive guide. For the whole colour range and order of draw, see blood draw tube colors. Other tube types in this family are covered in red top tube additive and gray top tube additive.
What coagulation tubes are
“Coagulation tubes” is the everyday name for evacuated blood collection tubes whose specimens are used for plasma-based coagulation testing. The standard that governs that specimen work is CLSI H21, Collection, Transport, and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays, sixth edition, which replaces CLSI H21-A5 published in 2008. Its stated scope is the collection, transport and processing of human specimens for plasma-based coagulation testing.
Who uses them: clinical laboratories and phlebotomy teams collect the specimens, and the staff who stock a draw station or a lab supply cupboard choose the product.
What the standard covers and what it excludes
CLSI’s product page for H21 says the guideline does not cover whole blood coagulation assays, platelet function tests, thrombin generation assays, point-of-care or molecular coagulation testing. A tube bought for those uses is therefore outside this standard’s scope. For point-of-care clotting measurement see activated clotting time.
The sixth edition removes the earlier recommendation for the 129 mmol/L, 3.8% form of trisodium citrate. It also describes specimens as susceptible to preexamination errors in collection, mixing, storage and transport, and adds a list of specimen collection issues of particular relevance to plasma-based coagulation testing. The CLSI product page does not give tube type, fill ratio or number of inversions.
Construction and additive: a manufacturer example
A specification page shows what the class looks like in practice. BD lists its Vacutainer citrate tube (SKU 363083) with the following values on its product page.
| Specification | Value listed for BD 363083 |
|---|---|
| Additive | Buffered sodium citrate (0.109M, 3.2%) |
| Closure | BD Hemogard closure, light blue |
| Draw volume | 2.7 (the page lists no unit) |
| Tube size | 13×75 |
| Electronic instructions for use | eIFU section on the product page, linking to BD’s general eIFU portal |
How to choose: what to verify
- Additive and concentration. Confirm the label or specification names the citrate form and strength. CLSI H21 sixth edition no longer recommends the 3.8% form.
- Intended test. Confirm the planned tests are plasma-based; whole blood, platelet function, thrombin generation, point-of-care and molecular testing are outside H21’s scope.
- Draw volume, tube size and closure. Read these from the product page for the SKU, as in the table above, and match them to the collection system in use.
- Instructions for use. Check that the manufacturer’s IFU is available for the SKU and read it for fill and mixing requirements, which the product page does not summarise.
A supplier document checklist for a draw station is in the phlebotomy lab supply checklist.
Handling basics and common mistakes
CLSI describes specimens referred for coagulation testing as susceptible to preexamination errors, including those arising in collection, mixing, storage and transport. Treat each as a place where the tube’s IFU and the laboratory’s own procedure apply. Common purchasing mistakes follow from the points above: choosing by closure colour without reading the SKU specification, assuming a citrate tube suits point-of-care or whole blood methods, and relying on the 3.8% recommendation that H21 sixth edition removed.
FAQ
What is a coagulation tube?
It is a blood collection tube used for specimens for plasma-based coagulation testing, such as the light blue-closure buffered 3.2% sodium citrate tube listed by BD under SKU 363083.
Does CLSI H21 specify the tube and fill ratio?
The CLSI product page for the sixth edition states its scope as collection, transport and processing of specimens for plasma-based coagulation testing; it does not state tube type or fill ratio. Those details are in the blue top tube additive guide and the manufacturer’s IFU.
Does H21 cover point-of-care clotting tests?
No. CLSI lists whole blood coagulation assays, platelet function tests, thrombin generation assays, and point-of-care and molecular coagulation testing as outside its scope.
Sources
- CLSI, H21 product page, Collection, Transport, and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays, 6th ed., clsi.org/standards/products/hematology/documents/h21, checked 2026-11-01.
- BD, Vacutainer citrate tubes, SKU 363083, bd.com product page, checked 2026-11-01.
