What is the Difference Between K2 EDTA and K3 EDTA

The main difference between K2 EDTA and K3 EDTA is that K2 EDTA contains two chelated potassium ions whereas K3 EDTA contains three chelated potassium ions. Furthermore, K2 EDTA slightly increases the MCV (mean corpuscular volume) of red blood cells at higher concentrations while K3 EDTA has no influence on the MCV of red blood cells at higher concentrations.

K2 EDTA and K3 EDTA are two types of anticoagulants used in routine hematological tests. However, their influence on the blood count remains controversial.

Key Areas Covered

1. What is K2 EDTA
     – Definition, Chelation, Importance
2. What is K3 EDTA
     – Definition, Facts, Drawbacks
3. What are the Similarities Between K2 EDTA and K3 EDTA
     – Outline of Common Features
4. What is the Difference Between K2 EDTA and K3 EDTA
     – Comparison of Key Differences

Key Terms

Anticoagulants, Hematological Tests, K2 EDTA, K3 EDTA, MCV

What is K2 EDTA

K2 EDTA (dipotassium ethylenediaminetetraacetic acid) is a strong anticoagulant used to store blood for complete blood counts (CBC) in blood collection tubes. Generally, whole blood is stored in these tubes. However, K2 EDTA contains two potassium ions bound to the EDTA molecule.

Figure 1: Chelation of Metal Ions by EDTA

Moreover, EDTA is a chelating agent which can sequester metal ions including ferric ions and calcium ions in a mixture, diminishing their reactivity. Therefore, the main function of K2 EDTA in the blood specimen is to chelate calcium ions from the mixture. Furthermore, the process of blood coagulation requires calcium ions. But, the addition of EDTA to the specimen makes the calcium ions unavailable for this process, arresting coagulation.

What is K3 EDTA

K3 ETDA is an alternative form of K2 EDTA used during collecting blood for the routine hematological tests. In comparison to K2 EDTA, K3 EDTA contains three potassium ions bound to EDTA. However, the International Council for Standardization in Haematology recommends K2 EDTA as the anticoagulant due to two reasons:

• the increasing EDTA concentration in K3 EDTA results in increasing the shrinkage of red blood cells (11% shrinkage with 7.5 mg/ml blood). and
• upon standing, K3 EDTA increases the cell volume largely.
  

  Figure 2: K2 EDTA Tube

Also, K3 EDTA lowers the MCV values up to -0.1 to -1.3% when compared to K2 EDTA. Another drawback of K3 EDTA is that it results in the dilution of the blood specimen. It lowers most of the measurements including RBC, WBC, platelet, and Hgb counts by 1-2%.

Similarities Between K2 EDTA AND K3 EDTA

• K2 EDTA and K3 EDTA are two types of anticoagulants used in routine blood tests.
• Both consist of potassium ions chelated by EDTA.
• Furthermore, the main function of both is to prevent blood coagulation during storage. This is by chelating calcium ions in the blood.
• Besides, both types of tubes come with lavender color tops.
• And, they are mainly used to collect blood for complete blood counts (CBC).
• Also, most of the molecular genetics laboratories prefer these EDTA tubes to collect blood for their genetic studies.

Difference Between K2 EDTA and K3 EDTA

Definition

K2 EDTA refers to a type of strong anticoagulant used during the collection of blood for CBCs while K3 EDTA refers to an alternative form of K2 EDTA used as an anticoagulant.

Known as

K2 EDTA is known as dipotassium ethylenediaminetetraacetic acid while K3 EDTA is known as tripotassium ethylenediaminetetraacetic acid.

Number of Potassium Ions

The main difference between K2 EDTA and K3 EDTA is that K2 EDTA contains two potassium ions while K3 EDTA contains three potassium ions.

Blood Collection Tubes

Another difference between K2 EDTA and K3 EDTA is that K2 EDTA solution is spray-dried in the interior surface of plastic tubes while K3 EDTA solution comes as a liquid in glass tubes.

Influence on MCV of Red Blood Cells

Moreover, K2 EDTA slightly increases the MCV at higher concentrations while K3 EDTA does not influence MCV at higher concentrations. Hence, this is another difference between K2 EDTA and K3 EDTA.

Effect on Packed Cell Volume

Furthermore, the packed cell volume of centrifuged blood decreases with the increasing K2 EDTA concentration while this decrease is more pronounced with K3 EDTA.

Conclusion

K2 EDTA is a type of anticoagulant used in the blood collections tubes to prevent blood coagulation during storage by chelating calcium ions required by the coagulation process. In comparison, K3 EDTA is an alternative form of EDTA used as an anticoagulant. However, K2 EDTA influences the MCV of red blood cells at higher concentrations while the increasing concentration of K3 EDTA influences the packed cell volume of the centrifuged blood. Therefore, the main difference between K2 EDTA and K3 EDTA is their influence on the results of the hematological tests.

References:

1. Goossens, W., et al. “K2- Or K3-EDTA: the Anticoagulant of Choice in Routine Haematology?” Clinical & Laboratory Haematology, vol. 13, no. 3, 2008, pp. 291–295., doi:10.1111/j.1365-2257.1991.tb00284.x.

Image Courtesy:

1. “Metal-EDTA” By Smokefootderivative work: Chamberlain2007 (talk) – Medta.png (Public Domain) via Commons Wikimedia  
2. “EDTA tube” By Awesomeguy78 – Own work (CC BY-SA 4.0) via Commons Wikimedia