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General product and laboratory information only; this is not medical advice and does not describe how to collect a specimen.
Short answer
K2 EDTA (also written K2EDTA) is the dipotassium salt of ethylenediaminetetraacetic acid, used as the anticoagulant in lavender-top blood collection tubes. EDTA binds calcium, which the clotting cascade needs, so the sample stays liquid and blood cells keep their shape for hematology testing. The additive amount is matched to the tube’s nominal draw volume, which is why underfilling matters.
What K2 EDTA means
“K2” marks the dipotassium form of the EDTA salt. Searches for k2edta, k2 edta tube and k2 edta tubes all refer to the same item: an evacuated blood collection tube whose additive is K2 EDTA. Tubes made with other EDTA salts also appear in the literature (a 2024 validation study mentions K3EDTA microtubes), but this page does not compare the salts.
In the United States, these tubes fall under the FDA product code GIM, “Tubes, Vacuum Sample, With Anticoagulant”, a class 2 device regulated under 21 CFR 862.1675 (blood specimen collection device). Source: openFDA device classification database, read 2026-11-07.
How EDTA prevents clotting
A review in Clinical Chemistry and Laboratory Medicine (Banfi, Salvagno and Lippi, 2007) explains that EDTA chelates calcium and several other metal ions. Calcium is necessary for the enzyme reactions of the coagulation cascade, and removing it “irreversibly prevents blood clotting within the collection tube”. The same review notes that EDTA has historically been recommended as the anticoagulant of choice for hematological testing because it allows the best preservation of cellular components and morphology of blood cells, and that no universal anticoagulant exists for every analyte.
FDA record: sizes and additive amounts
Original comparison: the table below is built from the FDA-linked AccessGUDID device records (queried through openFDA on 2026-11-07) for one manufacturer’s K2 EDTA tube line. Each record lists the additive amount in its product name and the tube dimensions and nominal volume in its description. The final column is simple arithmetic, not a stated specification.
| Additive per tube (record name) | Tube size (mm) | Nominal draw (mL) | Derived mg per mL |
|---|---|---|---|
| 3.6 mg K2 EDTA | 13 x 75 | 2.0 | 1.8 |
| 5.4 mg K2 EDTA | 13 x 75 | 3.0 | 1.8 |
| 7.2 mg K2 EDTA | 13 x 75 | 4.0 | 1.8 |
| 10.8 mg K2 EDTA | 13 x 100 | 6.0 | 1.8 |
All four records are single-use, prescription-use devices, and all carry a “LAV” (lavender) descriptor. The pattern to take away: the additive scales with the nominal volume, so the concentration is designed for a tube filled to its stated volume. Another manufacturer’s tubes may differ; the product’s own instructions for use govern.
Underfilling and low-volume tubes
A 2024 paper in the Journal of Medical Biochemistry, “Validation of low-volume blood collection tubes for routine hematologic testing”, tested spray-dried K2EDTA tubes on a Sysmex XN-10 analyzer. It reports that 0.5 mL of blood placed in a standard 3.0 mL K2EDTA tube produced clinically significant bias in hematocrit, MCV and MCHC. Its introduction cites earlier work (Lippi et al., Diagnosis, 2023) reporting that spray-dried evacuated K2EDTA tubes filled to less than 67% of nominal volume can give spurious red cell count, hemoglobin, hematocrit, MCV, MCHC and platelet-related results.
The authors concluded that low-volume K2EDTA tubes (the study used 0.25 to 0.5 mL tubes) could replace standard tubes where samples would otherwise be insufficient, for example with difficult veins, and help reduce iatrogenic anemia. The finding concerns the additive-to-blood ratio, not a flaw in K2 EDTA itself.
Where it matters for labs and clinics
- Hematology. EDTA is the traditional anticoagulant for cell counting and morphology (Banfi 2007).
- Other analytes. The same review discusses EDTA use for cytokines, proteins and peptides, cardiac markers and proteomics, and stresses that the choice of anticoagulant depends on the analyte.
- Tube identification. See the blood draw tube colors guide for how colour conventions map to additives.
- Sequence. Tube order is specified in order of draw for venipuncture and capillary order of draw.
- Contrast with serum tubes. For a tube built to clot rather than prevent clotting, see serum separation tubes.
Common misunderstandings
“EDTA tube” and “trypsin-EDTA” are the same thing
They are not. Trypsin-EDTA is a cell culture reagent for detaching adherent cells; it is a separate topic covered in trypsinization.
Any lavender tube is interchangeable
Lavender signals an EDTA tube, but the additive amount, fill volume and tube size vary by product, as the FDA records above show.
A small sample in a large tube is the same as a small sample in a small tube
The 2024 study above found it is not: the standard tube filled with 0.5 mL biased several indices.
FAQ
What is a K2 EDTA tube?
An evacuated blood collection tube whose anticoagulant is dipotassium EDTA, used mainly for hematology specimens and recognised by its lavender closure.
Is K2EDTA the same as K2 EDTA?
Yes. Both spellings name the same additive; the FDA records write “K2EDTA” in the device description and “K2 EDTA” in the brand name.
Why does fill volume matter?
The additive amount is set for the nominal draw volume (1.8 mg per mL in the records above, by arithmetic). Published work reports spurious results when tubes are filled below about 67% of nominal volume.
Is a K2 EDTA tube a regulated device?
In the US it falls under FDA product code GIM, class 2, 21 CFR 862.1675.
Sources
- openFDA device classification, product code GIM: api.fda.gov/device/classification (read 2026-11-07).
- openFDA / AccessGUDID UDI records, K2EDTA under GIM: api.fda.gov/device/udi (read 2026-11-07).
- Banfi G, Salvagno GL, Lippi G. The role of ethylenediamine tetraacetic acid (EDTA) as in vitro anticoagulant for diagnostic purposes. Clin Chem Lab Med 2007;45(5):565-76. doi:10.1515/CCLM.2007.110, PMID 17484616 (abstract read 2026-11-07).
- Validation of low-volume blood collection tubes for routine hematologic testing. J Med Biochem 2024. PMC11771976 (read 2026-11-07).
