K3 EDTA Blood Collection Tubes

DESCRIPTION

K3 EDTA (Tripotassium Ethylenediaminetetraacetic Acid) blood collection tubes are a staple in clinical laboratories, primarily used for hematology testing. They are easily identified by their lavender or purple-colored caps.

Here is a breakdown of how they work and why they are used.

How It Works: The Anticoagulant Mechanism

The primary role of K3 EDTA is to prevent blood from clotting. It achieves this through a process called chelation:

• Calcium Binding: EDTA binds to calcium ions ($Ca^{2+}$) in the blood.

• Clotting Inhibition: Since calcium is a vital cofactor in the coagulation cascade, its removal effectively “freezes” the clotting process.

• Cell Preservation: Unlike some other anticoagulants, EDTA is excellent at maintaining the morphology (shape and size) of red blood cells, white blood cells, and platelets.

  Common Clinical Applications

  These tubes are used whenever a “whole blood” sample is needed for cellular analysis. Common tests include:

  • Complete Blood Count (CBC): Measuring hemoglobin, hematocrit, and cell counts.

  • Blood Film/Smear: Manual differential count of white blood cells.

  • HbA1c: Monitoring long-term glucose levels in diabetic patients.

  • Blood Grouping: Determining ABO/Rh types and cross-matching for transfusions.

  Important Considerations

  K2 vs. K3 EDTA

  You might also see K2 EDTA (Dipotassium) tubes. While both serve the same purpose, there are minor differences:

  • K3 EDTA is usually a liquid additive. This can slightly dilute the sample (about 1-2%), which may affect some very sensitive cell volume measurements.

  • K2 EDTA is typically spray-dried onto the walls and is the current recommendation by the ICSH (International Council for Standardization in Haematology) for most routine testing.

  The “Order of Draw”

  Because EDTA is rich in potassium and binds calcium, it must be drawn after serum tubes and heparin tubes. If drawn too early, “carryover” of the EDTA into other tubes can cause falsely high potassium readings or falsely low calcium readings in chemistry panels.