A Phlebotomy Guide to Colour-Coded Blood Tubes

Article by: Sharon Wong Shi May

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When you get your blood drawn by a phlebotomist, your blood is placed into several tubes with different cap colors. But, why use so many tubes for just a few cm3 of blood? Here, we will explore the purpose behind some of the most common colour-coded tubes used.

What are serum and plasma?

A serum is the clear part of the blood after the blood clot whereas a plasma is the clear part of the blood when blood clotting is prevented by an anticoagulant (Bayot and Tadi, 2023). Tubes with red and gold tops are used to collect serum whereas other colours, such as lavender, grey, green, and light blue, are used to collect whole blood or plasma.

Red top tube (Glass or plastic type)

In a glass red top tube, there are no additives or anticoagulants inside. The blood will clot after touching the wall of the tube. It is used for blood bank tests. Whereas, a plastic red top tube has a clot activator to promote blood clots (University of California, Irvine, n.d.).

Gold top tube

This tube has a clot activator and serum gel separator to speed up blood clotting. It is usually used for several diagnostic tests, including serology and immunology tests (University of California, Irvine, n.d.).

Lavender top tube

This tube contains ethylene-diamine-tetra-acetic acid (EDTA), an anticoagulant that prevents blood clotting by chelating calcium ions in the blood. Calcium ion is essential for the formation of thromboplastin, as it converts prothrombin to thrombin (Kasabe and Ahire, 2021). Typically, the blood collected using this tube is used for hematologic assays to study the blood for any blood-related disorders (Bayot and Tadi, 2023).

Grey top tube

It contains potassium oxalate as an anticoagulant to bind to calcium ions in the blood to prevent blood clotting. Besides that, sodium fluoride is also present and acts as an antiglycolytic agent. Therefore, the glucose in the whole blood can be preserved and used for plasma glucose and lactic acid testing (Bayot and Tadi, 2023; University of California, Irvine, n.d.).

Green  top tube

This tube contains heparin, an anticoagulant that prevents the formation of thrombin. Thrombin is important for converting fibrinogen to fibrin fibers, which trap platelets and facilitate blood clotting (Bayot and Tadi, 2023; Kasabe and Ahire, 2021). 

Light blue top tube

This tube contains 3.2% sodium citrate to prevent the coagulation of blood and is typically used for blood clotting studies (Bayot and Tadi, 2023).

Royal blue top tube

This tube may or may not contain anticoagulant EDTA and is used in trace element analysis (such as zinc and lead), toxicology, and nutritional studies of the blood (Maria, 2024).

In conclusion, colour-coded blood collection tubes serve several purposes. They help prevent confusion, ensure the blood is properly prepared for specific tests, facilitate efficient workflow, ensure accurate results, and prevent cross-contamination among the samples. It is important to note that the colour of the tubes may vary by manufacturer (Bayot and Tadi, 2023).

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Citations:

Bayot, M.L. and Tadi, P. (2023). Laboratory Tube Collection. [online] PubMed. Available at: https://www.ncbi.nlm.nih.gov/books/NBK555991/ 

Kasabe, S.M. and Ahire, B.B. (2021). Role of Calcium in Blood Coagulation. International Journal of Advanced Research in Science, Communication and Technology (IJARSCT), [online] 2(2), p.2581. doi:https://doi.org/10.48175/IJARSCT-793

Maria, E.Q. (2024). Understanding the Royal Blue Top Tube: Essential Guide for EDTA Blood Collection (13X100MM, 6ML, PET). [online] QV Medical Supplies. Available at: https://qvmedicalsupplies.com/blogs/laboratory-essential-blogs/understanding-the-royal-blue-top-tube-essential-guide-for-edta-blood-collection-13x100mm-6ml-pet

University of California, Irvine (n.d.). Specimen Requirements/Containers | Department of Pathology | School of Medicine | University of California, Irvine. [online] www.pathology.uci.edu. Available at: https://www.pathology.uci.edu/services/specimen-containers.asp