What is EDTA Tube?

EDTA tube is what we often call a purple-top tube, used for routine blood testing.

EDTA refers to ethylenediaminetetraacetate, an anticoagulant for blood collection tubes.

EDTA salt can protect the cellular components of blood, does not affect the white blood cell count and size, has minimal effect on the morphology of red blood cells, and can inhibit platelet aggregation, so it is used for routine blood testing.

EDTA salts are subdivided into K2 EDTA and K3 EDTA

K2 EDTA refers to ethylenediaminetetraacetic acid dipotassium salt.

K3 EDTA refers to ethylenediaminetetraacetic acid tripotassium salt.

We prefer K2 EDTA as an anticoagulant because K2 EDTA is less soluble and slower to anticoagulant than K3 EDTA.

What is the difference between K2 EDTA and K3 EDTA?

The difference in physical properties:

●K2 EDTA solution is spray-dried inside the plastic tube.

●K3 EDTA solution is liquid in the glass tube and spray-dried inside the plastic tube.

Differences in clinical use:

The International Committee for Standardization in Hematology and the NCCLS (CLSI) recommend K2 EDTA as a specialized anticoagulant for blood cell counts and volume measurements.

The reasons are as follows.

● If EDTA concentration increases, K3 EDTA is more likely to cause crinkling of red blood cells than K2 EDTA. (When the concentration of K3 EDTA reaches 7.5 mg/ml, 11% of erythrocytes will undergo crumpling)

● If the specimen is left for a period of time, K3 EDTA is more likely to cause the problem of cell volume increase compared to K2 EDTA (1.6% volume increase when left for 4 hours)

● K3 EDTA is more likely to cause a decrease in mean erythrocyte volume (MCV) than K2 EDTA (usually a negative deviation of -0.1 to -1.3% compared to K2 EDTA)

● If K3 EDTA is used as a liquid additive, it can lead to dilution of the sample. All direct assays, such as hemoglobin, red blood cells, white blood cells, and platelet count, are 1 to 2% lower than K2 EDTA as an anticoagulant.

BRUNSON et al. reported good agreement between plastic K2 EDTA tubes and glass tubes of K3 EDTA in detecting cell counts and classification. However, as previously shown, errors of 1 to 2% due to dilution were also reported.