EDTA, or Ethylenediaminetetraacetic acid, is a chelating agent that binds to metal ions. It was first synthesized in the 1930s and has since found widespread use in various industries, including medicine, food processing, and cleaning products. In the medical field, its primary role is as an anticoagulant in blood collection tubes.
Chemical Properties of EDTA
EDTA is a molecule composed of four carboxyl groups and two amine groups. Its structure allows it to bind tightly to divalent metal ions such as calcium and magnesium. This binding capability gives EDTA Tubes, it anticoagulant properties, as calcium ions are essential for blood clotting. By sequestering these ions, EDTA effectively prevents the coagulation cascade, maintaining the blood in a fluid state suitable for analysis.
The Role of EDTA in Blood Collection
Anticoagulant Properties
The primary reason for using EDTA in purple top tubes is its powerful anticoagulant properties. When blood is collected, the natural clotting process begins immediately. Without an anticoagulant, the blood sample would coagulate, rendering it unusable for many analyses. By binding to calcium ions, EDTA inhibits the clotting process, preserving the sample in a liquid state.
Preventing Coagulation
Blood coagulation involves a complex cascade of reactions, with calcium ions playing a pivotal role. EDTA cheats these ions, effectively removing them from the reaction pathway. This action prevents the formation of fibrin clots, ensuring that the blood remains fluid and easy to work with for laboratory tests.
EDTA’s Interaction with Calcium
Calcium ions are necessary for the activation of clotting factors in the blood. EDTA’s ability to bind these ions means it can effectively halt coagulation. This rapid and stable interaction makes EDTA an ideal choice for preserving blood samples for extended periods.
What is Purple Top Tubes?
Purple top tubes are blood collection tubes that contain EDTA (Ethylenediaminetetraacetic acid) as an anticoagulant. They are primarily used in hematology tests, such as complete blood counts (CBC), due to their ability to preserve the shape and size of blood cells and prevent clotting. The distinctive purple cap ensures quick identification, standardizing the blood collection process in medical laboratories and ensuring the accuracy of diagnostic results.
Why Purple Top Tubes?
Color-Coding in Blood Collection
Color-coded tubes streamline blood collection in clinical settings and ensure the correct additives are used for specific tests. The purple top tube, universally associated with EDTA, allows healthcare professionals to quickly and reliably identify the correct tube for complete blood counts (CBC) and other hematology tests
Standardization in Medical Testing
Standardization is critical in medical testing to ensure consistency and reliability of results. The use of purple top tubes for EDTA-containing samples is a widely accepted standard. This consistency helps to avoid confusion and errors in the blood collection process, contributing to the overall accuracy of diagnostic tests.
How EDTA prevents blood clotting in purple top tubes
The mechanism by which EDTA prevents blood clotting in purple top tubes is a fascinating example of the intricate interplay between chemistry and biology. When blood is drawn into a purple top tube, the EDTA immediately begins binding to the calcium ions in the sample.

Calcium ions play a critical role in coagulation, serving as cofactors for various enzymes involved in the clotting cascade. By sequestering these calcium ions, EDTA effectively disrupts the normal functioning of the clotting system, preventing the formation of fibrin. This insoluble protein forms the backbone of a blood clot.
EDTA does not absolutely prevent blood clotting; it simply delays the coagulation process, providing a window of time during which you can process and analyze the blood sample. This window can vary depending on factors such as the concentration of EDTA in the tube, the volume of the blood sample, and the storage conditions.