EDTA K2 and EDTA K3
K2 EDTA and K3 EDTA are two types of anticoagulants used in routine hematological tests.
However, their influence on the blood count remains controversial.
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.
It should be emphasized that irrespective of the EDTA salt used for anticoagulation, all tubes must be inverted 8-10 times to ensure thorough mixing of the blood with the anticoagulant.
Clinical Differences:
The International Council for Standardization in Haematology and NCCLS have recommended K2 EDTA as the anticoagulant of choice for blood cell counting and sizing for the following reasons:
• K3 EDTA results in greater RBC shrinkage with increasing EDTA concentrations
(11% shrinkage with 7.5 mg/ml blood).
• K3 EDTA produces a larger increase in cell volume on standing (1.6% increase after 4 hours).
• K3 EDTA leads to lower MCV values (typically a -0.1 to -1.3% difference is observed compared with K2 EDTA).
• K3 EDTA is a liquid additive, and therefore, will result in the dilution of the specimen. All directly measured values (Hgb, RBC, WBC, and platelet counts) have been reported to be 1-2% lower than results obtained with K2 EDTA.
• With some instrument systems, K3 EDTA gives lower WBC counts when used at high concentrations. Brunson, et al., reported that plastic tubes containing K2 EDTA gave complete blood count and differential results in excellent agreement with glass tubes containing K3 EDTA, though they confirmed the earlier results of 1-2% higher WBC, RBC, hemoglobin, and platelet count results with the former tube, owing to dilution observed with K3 EDTA.
• Our internal studies showed no clinically significant differences when comparing K3 EDTA glass tubes to K2EDTA plastic tubes.